Ebook Bone and joint imaging (3rd edition): Part 2

(BQ) Part 2 book "Bone and joint imaging" presents the following contents: Infectious diseases, traumatic diseases, internal derangement of joints, thermal, iatrogenic, nutritional, and neurogenic diseases, tumors and tumor like diseases, congenital diseases, diseases of soft tissue and muscle,...

Infectious Diseases

C H A P T E R 5 3

Osteomyelitis, Septic Arthritis, and

Soft Tissue Infection: Mechanisms

and Situations

SUMMARY OF KEY FEATURES

A thorough understanding of regional anatomy is

fundamental to the accurate interpretation of clinical,

radiographic, and pathologic characteristics of infections

of bone, joint, and soft tissue In most persons with such

infections, a specific mechanism of contamination can

be recognized; infection may be derived from

hematogenous seeding, spread from a contiguous

source, direct implantation, or operative contamination

The radiographic findings of osteomyelitis (including

abscess, involucrum, and sequestration), septic arthritis

(including joint space loss and marginal and central

osseous erosions), and soft tissue suppuration (including

swelling, radiolucent streaks, and periostitis) are generally

delayed for a variable period after the clinical onset of

infection Other diagnostic techniques, including

scintigraphy and magnetic resonance imaging, allow an

accurate diagnosis at an earlier stage of the process

INTRODUCTION

Infection of bone, joint, and soft tissue is a common and

disturbing problem that often represents a diagnostic and

therapeutic challenge Early diagnosis is imperative because

it allows prompt treatment, which can prevent many of

the dreaded complications

TERMINOLOGY

Ostemyelitis implies an infection of bone and marrow It most

commonly results from bacterial infections, although fungi,

parasites, and viruses can infect the bone and the marrow

Infective (suppurative) osteitis indicates contamination

of the bone cortex Infective osteitis can occur as an

iso-lated phenomenon or, more frequently, as a concomitant

to osteomyelitis

Infective (suppurative) periostitis implies contamination

of the periosteal cloak that surrounds the bone In this

situation, a subperiosteal accumulation of organisms

fre-quently leads to infective osteitis and osteomyelitis

Soft tissue infection indicates contamination of cutaneous,

subcutaneous, muscular, fascial, tendinous, ligamentous,

or bursal structures This may be seen as an isolated

condi-tion or as a complicacondi-tion of periosteal, osseous, marrow,

or articular infection

713

Articular infection implies a septic process of the joint

itself Septic arthritis can occur as an isolated conditionthat may soon spread to the neighboring bone or as acomplication of adjacent osteomyelitis or soft tissueinfection

A sequestrum represents a segment of necrotic bone

that is separated from living bone by granulation tissue.Sequestra may reside in the marrow for protracted periods,harboring living organisms that have the capability ofevoking an acute flare-up of the infection

An involucrum denotes a layer of living bone that has

formed about the dead bone It can surround and tually merge with the parent bone

even-Cloaca is an opening in the involucrum through which

granulation tissue and sequestra can be discharged

Sinuses are tracts leading to the skin surface from the

bone

A bone abscess (Brodie’s abscess) is a sharply delineated

focus of infection It is of variable size, can occur at single

or multiple locations, and represents a site of active tion It is lined by granulation tissue and frequently issurrounded by eburnated bone

infec-Garré’s sclerosing osteomyelitis is a sclerotic, nonpurulent

form of osteomyelitis Although this term is applied lessly to any form of osteomyelitis with severe osseouseburnation, it should be reserved for those cases in whichintense proliferation of the periosteum leads to bonydeposition and in which no necrosis or purulent exudateand little granulation tissue are present

care-The clinical stages of osteomyelitis are frequently nated acute, subacute, and chronic This does not implythat definitive divisions exist between one stage andanother, nor does it signify that all cases of osteomyelitisprogress through each of these phases The relativelyabrupt onset of clinical symptoms and signs during theinitial stage of infection is a clear indication of the acuteosteomyelitic phase; if this acute phase passes withoutcomplete elimination of infection, subacute or chronicosteomyelitis can become apparent The transition fromacute to subacute and chronic osteomyelitis may indicatethat therapeutic measures have been inadequate

desig-OSTEOMYELITISRoutes of ContaminationOsseous (and articular) structures can be contaminated

by four principal routes:

1 Hematogenous spread of infection Infection can reach

the bone (or joint) via the bloodstream

2 Spread from a contiguous source of infection Infection can

extend into the bone (or joint) from an adjacent taminated site Cutaneous, sinus, and dental infectionsare three important sources of extraskeletal infective foci

con-3 Direct implantation Direct implantation of infectious

material into the bone (or joint) may occur following

puncture or penetrating injuries

4 Postoperative infection Postoperative infection may

occur via direct implantation, spread from a

con-tiguous septic focus, or hematogenous contamination

of the bone (or joint)

Hematogenous Infection

Bacteremia

Bacteria usually enter the blood vessels (or the

lym-phatics and then the blood vessels) by direct extension

from extravascular sites of infection, which include the

genitourinary, gastrointestinal, biliary, and respiratory

systems; the skin and soft tissue; and other structures In

some instances, no primary source of infection is

iden-tifiable Bacteremia is often transient and totally

asymp-tomatic; however, in some cases, prominent clinical

manifestations may occur

A single pathogenic organism is usually responsible

for hematogenous osteomyelitis In neonates and infants,

Staphylococcus aureus, group B streptococcus, and Escherichia

coli are the bone isolates recovered most frequently In

children older than 1 year of age, S aureus, Streptococcus

pyogenes, and Haemophilus influenzae are responsible for

most cases of hematogenous osteomyelitis In those older

than 4 years, staphylococci are the major pathogens in

this disease, as the prevalence of osteomyelitis related to

H influenzae decreases Gram-negative organisms assume

importance as pathogens in bone and joint infections in

adults and in intravenous drug abusers A recent surgical

procedure or concurrent soft tissue infection is frequently

associated with staphylococcal septicemia and

osteomye-litis; disorders of the gastrointestinal or genitourinary tract

may initiate a gram-negative septicemia; and an acute or

chronic respiratory infection is important in the

patho-genesis of tuberculous, fungal, and pneumococcal

osteo-myelitis Blood cultures are positive in approximately

50% of patients with acute hematogenous osteomyelitis

General Clinical Features

Childhood osteomyelitis can be associated with a sudden

onset of high fever, a toxic state, and local signs of

inflam-mation, although this presentation is not uniform Indeed,

as many as 50% of children have vague complaints,

including local pain of 1 to 3 months’ duration with

mini-mal if any temperature elevation In infants,

hematoge-nous osteomyelitis often leads to less dramatic findings,

including pain, swelling, and an unwillingness to move

the affected bones

The adult form of hematogenous osteomyelitis may

have a more insidious onset, with a relatively longer

period between the appearance of symptoms and signs

and accurate diagnosis In all age groups, the prior

administration of antibiotics for treatment of the febrile

state can attenuate or alter the clinical (and imaging)

manifestations of the bone infection Single or multiple

bones can be infected; involvement of multiple osseous

sites appears to be particularly common in infants In the

younger age group, the long tubular bones of the ities are especially vulnerable; in adults, hematogenousosteomyelitis is encountered more frequently in the axialskeleton

extrem-Vascular Anatomy

The vascular supply of a tubular bone is derived fromseveral points of arterial inflow, which become compli-cated sinusoidal networks within the bone (Fig 53–1).One or two diaphyseal nutrient arteries pierce the cortexand divide into ascending and descending branches Asthey extend to the ends of the bones, they branch repeat-edly, becoming finer channels, and are joined by theterminals of metaphyseal and epiphyseal arteries Themetaphyseal arteries originate from neighboring systemicvessels, whereas the epiphyseal arteries arise from peri-articular vascular arcades The arteries within the bonemarrow form a series of cortical branches that connectwith the fenestrated capillaries of the haversian systems

At the bony surface, the cortical capillaries form nections with overlying periosteal plexuses, which them-selves are derived from the arteries of the neighboringmuscles and soft tissues The cortices of the tubularbones derive nutrition from both the periosteal and themedullary circulatory systems The central arteriolesdrain into a thin-walled venous sinus, which subsequentlyunites with veins that retrace the course of the nutrientarteries, piercing the cortex at various points and joininglarger and larger venous channels

con-Joints receive blood vessels from periarterial plexusesthat pierce the capsule to form a vascular plexus in thedeeper part of the synovial membrane The blood vessels

of the synovial membrane terminate at the articularmargins as looped anastomoses (circulus articularis vascu-losus) The epiphysis and the adjacent synovium share acommon blood supply

The radiographic and pathologic features of myelitis differ in children, infants, and adults, related inlarge part to peculiarities of the vascular anatomy of thetubular bones in each age group (Fig 53–2; Table 53–1)

osteo-Childhood Pattern. Between the age of approximately

1 year and the time when the open cartilaginous growthplates fuse, a childhood vascular pattern can be recog-

nized in the ends of the tubular bones (see Fig 53–2A).

In the metaphysis, the vessels turn in acute loops to joinlarge sinusoidal veins, which occupy the intramedullaryportion of the metaphysis; here, the blood flow is slowand turbulent The epiphyseal blood supply is distinctfrom that on the metaphyseal aspect of the plate Thisanatomic characteristic explains the peculiar predilection

of hematogenous osteomyelitis to affect metaphyses andequivalent locations in children

Infantile Pattern. A fetal vascular arrangement may persist

in some tubular bones up to the age of 1 year (see Fig

53–2B) Some vessels at the surface of the metaphysis

penetrate the preexisting growth plate, ramifying in theepiphysis This arrangement affords a vascular connectionbetween the metaphysis and epiphysis and explains thefrequency of epiphyseal and articular infection in infants

Adult Pattern. With narrowing and closing of the physealgrowth plate, metaphyseal vessels progressively reestab-lish a vascular connection between the metaphysis and

the epiphysis (see Fig 53–2C) Blood within the nutrient

vessels can then reach the surface of the epiphysisthrough large anastomosing channels

Age-Related Patterns

The development of hematogenous osteomyelitis variesaccording to age-related characteristics of the bones (Fig.53–3; Table 53–2)

Childhood. In childhood hematogenous osteomyelitis,the metaphyseal location is related to (1) the peculiaranatomy of the vascular tree, (2) the inability of vessels topenetrate the open physeal plate, (3) the slow rate ofblood flow in this region, (4) a decrease in phagocyticability of neighboring macrophages, or (5) secondarythrombosis of the nutrient artery Primary involvement

of an epiphysis or secondary extension across the physis

to an epiphysis is encountered rarely

Inflammation in the adjacent bone of the metaphysis

is characterized by vascular engorgement, edema, cellularresponse, and abscess formation Transudates extend from

Figure 53–1. Normal osseous circulation to a growing tubular

bone Nutrient arteries (1) pierce the diaphyseal cortex and

divide into descending and ascending (2) branches These latter

vessels continue to divide, becoming fine channels (3) as they

approach the end of the bone They are joined by metaphyseal

vessels (4) and, in the subepiphyseal (growth) plate region, form

a series of end-arterial loops (5) The venous sinuses extend from

the metaphyseal region toward the diaphysis, uniting with other

venous structures (6) and eventually piercing the cortex as a

large venous channel (7) At the ends of the bone, nutrient arteries

of the epiphysis (8) branch into finer structures, passing into the

subchondral region At this site, arterial loops (9) are again

evi-dent, some of which pierce the subchondral bone plate before

turning to enter the venous sinusoid and venous channels of the

epiphysis (10) At the bony surface, cortical capillaries (11) form

connections with overlying periosteal plexuses (12) Note that

in the growing child, distinct epiphyseal and metaphyseal arteries

can be distinguished on either side of the cartilaginous growth

plate Anastomoses between these vessels either do not occur or

are infrequent.

Figure 53–2. Normal vascular patterns of tubular bone, based

on age A, In the child, the capillaries of the metaphysis turn sharply, without violating the open growth plate B, In the infant,

some metaphyseal vessels may penetrate or extend around the

open growth plate, ramifying in the epiphysis C, In the adult,

with closure of the growth plate, a vascular connection between the metaphysis and epiphysis can be recognized.

TABLE 53–1

Vascular Patterns of Tubular Bones

Pattern Age (yr) Characteristics

Infantile 0–1* Diaphyseal and metaphyseal

vessels may perforate opengrowth plate

Childhood 1–16† Diaphyseal and metaphyseal

vessels do not penetrate opengrowth plate

Adult >16 Diaphyseal and metaphyseal

vessels penetrate closedgrowth plate

*Upper age limit depends on specific local anatomic variation in the appearance and growth of the ossification center.

† Upper age limit is related to the time at which the open growth plate closes.

the marrow to the adjacent cortex A rise in intramedullary

pressure, caused by the presence of inflammatory and

edematous tissue confined by the rigid cortical columns

of bone, encourages the extension of infected fluid by

way of haversian and Volkmann’s canals The

inflam-matory process soon reaches the outer surface of the

cortex and abscesses develop, lifting the periosteum and

disrupting the periosteal blood supply to the external

cortical surface Elevation of the periosteum is

promi-nent in the immature skeleton because of its relatively

loose attachment to the subjacent bone The elevated

periosteum produces single or multiple layers of bone(i.e., periostitis) and eventually lays down bone in theform of an involucrum Infection may penetrate theperiosteal membrane, producing cloacae (Fig 53–4).Childhood hematogenous osteomyelitis is not confined

to tubular bones In flat or irregular bones such as thecalcaneus, clavicle, and bones of the pelvis, childhoodosteomyelitis may show a predilection for metaphyseal-equivalent osseous locations adjacent to an apophysealcartilaginous plate and epiphyseal-equivalent locationsadjacent to articular cartilage

Infancy. In infants, because some of the vessels in themetaphysis penetrate the growth plate, a suppurativeprocess of the metaphysis may extend into the epiphysis(Fig 53–5) Epiphyseal infection can then result inarticular contamination and damage to the cells on theepiphyseal side of the growth cartilage, leading to arrest

or disorganization of growth and maturation Articularinvolvement is also facilitated by the frequent localization

of infantile osteomyelitis to the ends of bones in whichthe growth plate is intra-articular (e.g., hip)

Adulthood. Unique manifestations of hematogenousosteomyelitis are seen in adults (see Table 53–2) Thedisease in the mature skeleton does not commonly localize

in the tubular bones; hematogenous osteomyelitis of thespine, pelvis, and small bones is more common in adultpatients In cases in which involvement of tubular bones

is evident, the free communication of the metaphysealand epiphyseal vessels through the closed growth plateallows infection to localize in the subchondral (beneaththe articular cartilage) regions of the bone (Fig 53–6).Joint contamination can complicate this epiphyseallocation

The firm attachment of the periosteum to the cortex

in adults resists displacement; therefore, subperiostealabscess formation, extensive periostitis, and involucrumformation are relatively unusual in this age group Exten-sive sequestration is not a common feature In adults,infection violates and disrupts the cortex itself, producingatrophy and osseous weakening, and predisposes the bone

to pathologic fracture

Figure 53–3. Sites of hematogenous osteomyelitis of tubular

bone, based on age A, In the child, a metaphyseal focus is

frequent From this site, cortical penetration can result in a

subperiosteal abscess in locations where the growth plate is

extra-articular (1) or in a septic joint in locations where the

growth plate is intra-articular (2) B, In the infant, a

metaphy-seal focus may be complicated by epiphymetaphy-seal extension, owing

to the vascular anatomy in this age group C, In the adult, a

subchondral focus in an epiphysis is not unusual, owing to the

vascular anatomy in this age group.

A

C

B

TABLE 53–2

Hematogenous Osteomyelitis of Tubular Bones

Localization Metaphyseal with Metaphyseal Epiphyseal

epiphyseal extension

Pathologic fracture Not common Not common Common*

*In neglected cases.

B

Figure 53–4. Hematogenous osteomyelitis of tubular bone in a

child A, Sequential steps in the

initiation and progression of infection: 1, a metaphyseal focus

is common; 2, the infection spreads laterally, reaching and invading the cortical bone; 3, cortical penetration is associated with subperiosteal extension and elevation of the periosteal mem- brane; 4, subperiosteal bone for- mation leads to an involucrum or shell of new bone; 5, the involu- crum may become massive with

continued infection B, Lytic

metaphyseal focus in the femur is readily apparent It extends to the growth cartilage (causative organ-

ism is Staphylococcus).

Radiographic and Pathologic Abnormalities

Acute Hematogenous Osteomyelitis

The pathologic changes associated with acute

hematoge-nous pyogenic osteomyelitis are described in Table 53–3

Radiographic evidence of significant osseous destruction

is delayed for a period of days to weeks Nevertheless,

initial and subtle radiographic changes in the soft tissues

may appear within 3 days after bacterial contamination of

bone, although radiographically evident bone

destruc-tion and periostitis can be delayed for 1 to 2 weeks

Even-tually, large destructive lesions become evident on the

radiograph In children, these lesions appear as

enlarg-ing, poorly defined lucent shadows of the metaphysis,

surrounded by varying amounts of eburnation; the lucent

lesions extend to the growth plate and, on rare occasions,

may violate it In addition, destruction progresses

hori-zontally, reaching the cortex, and periostitis follows In

infants, the epiphyses are unossified or only partially

ossi-fied, making radiographic recognition of epiphyseal

destruction extremely difficult Metaphyseal lucent lesions,

periostitis, and joint effusion are helpful radiographic

clues In adults, soft tissue alterations are more difficult

to detect on radiographic examination Epiphyseal,

meta-physeal, and diaphyseal osseous destruction creates

radi-olucent areas of varying size, which are associated with

mild periostitis Cortical resorption can be identified as

endosteal scalloping, intracortical lucent regions ortunneling, and poorly defined subperiosteal bony defects

Subacute and Chronic Hematogenous Osteomyelitis

Brodie’s Abscess. Single or multiple radiolucent abscessesmay be evident during subacute or chronic stages ofosteomyelitis These abscesses are now defined ascircumscribed lesions showing a predilection for (but notconfined to) the ends of tubular bones; they are foundcharacteristically in subacute pyogenic osteomyelitis andare usually of staphylococcal origin It has been suggestedthat bone abscesses develop when an infective organismhas a reduced virulence or when the host demonstratesincreased resistance to infection Brodie’s abscesses areespecially common in children, more typically in boys Inthis age group, they appear in the metaphysis, particu-larly that of the distal or proximal portion of the tibia Inyoung children and infants, Brodie’s abscesses may occur

in epiphyses

Radiographs outline radiolucent areas with adjacentsclerosis (Fig 53–7) This lucent region is commonlylocated in the metaphysis, where it may connect with the

Figure 53–5. Hematogenous osteomyelitis of tubular bone

in an infant In this infant with acute staphylococcal

osteomyelitis, metaphyseal and epiphyseal involvement of the

distal end of the femur is associated with periostitis and

articular involvement. Figure 53–6. Hematogenous osteomyelitis of tubular bone

in an adult Epiphyseal localization is not infrequent in this age group Observe the lytic lesion (abscess), with surrounding

sclerosis extending to the subchondral bone plate (arrows).

Metaphyseal and diaphyseal sclerosis is evident The elongated shape of the lesion is typical of infection (causative organism is

Staphylococcus).

growth plate by a tortuous channel Radiographic

detec-tion of this channel is important; identificadetec-tion of a

meta-physeal defect connected to the growth plate by such a

tract ensures the diagnosis of osteomyelitis In the

di-aphysis, the radiolucent abscess cavity may be located in

central or subcortical areas of the spongiosa or in the

cortex itself and may contain a central sequestrum In an

epiphysis, a circular, well-defined osteolytic lesion is seen,

which, in the immature skeleton, may border on the

chondro-osseous junction or on the physis, where it may

extend into the metaphysis When an abscess is located in

the cortex, its radiographic appearance, consisting of a

lucent lesion with surrounding sclerosis and periostitis,

simulates that of an osteoid osteoma or stress fracture A

rounded radiolucent lesion without calcification is

characteristic of a cortical abscess; a circular lucent area

with or without calcification that is smaller than 2 cm is

more typical of an osteoid osteoma; and a linear lucent

shadow without calcification is characteristic of a stress

fracture In any skeletal location, computed tomography

(CT) or magnetic resonance (MR) imaging can be used

to better assess the extent of the abscess and any signs of

its reactivation (Fig 53–8)

Sequestration. During the course of hematogenous

osteomyelitis, cortical sequestration may become evident

One or more areas of osseous necrosis are commonlysituated in the medullary aspect of a tubular bone(sequestration is less prominent in flat bones), where theycreate radiodense bony spicules (Fig 53–9) The seques-trum frequently is marginated sharply, surrounded bygranulation tissue Sequestra may extrude through cor-tical breaks, extending into the adjacent soft tissues, wherethey eventually may be discharged through draining sinuses

Sclerosing Osteomyelitis. In the subacute and chronicstages of osteomyelitis, considerable periosteal boneformation can surround the altered cortex, and anincreased number and size of spongy trabeculae canreappear in the affected marrow, leading to considerableradiodensity and contour irregularity of the affected bone(Fig 53–10) Cystic changes may occur within the scle-rotic area, but sequestra are uncommon At any site, theradiographic findings of sclerosing osteomyelitis resem-ble those of osteoid osteoma, fibrous dysplasia, and Ewing’ssarcoma

Infection from a Contiguous Source

General Clinical Features

In most cases of osteomyelitis and septic arthritis arisingfrom such a contiguous source, soft tissue infections are

Figure 53–7. Brodie’s abscess: radiographic abnormalities Lateral radiograph outlines a typical appearance of an abscess of the distal end of the tibia caused by staphylococci Observe the elongated radiolucent lesion, with surrounding sclerosis

extending to the closing growth plate (arrows) The

channel-like shape of the lesion is important in the accurate diagnosis of this condition.

TABLE 53–3

Hematogenous Osteomyelitis: Radiographic-Pathologic

Correlation

Pathologic Abnormality Radiographic Abnormality

Vascular changes and edema Soft tissue swelling with

of soft tissues obliteration of tissue planes

Infection in medullary space Osteoporosis, bone lysis

with hyperemia, edema,

abscess formation, and

trabecular destruction

Infection in haversian and Increasing lysis, cortical

Volkmann’s canals of cortex lucency

Subperiosteal abscess Periostitis, involucrum

formation with lifting formation

of the periosteum and

bone formation

Infectious penetration of Soft tissue swelling, mass

periosteum with soft tissue formation, obliteration of

abscess formation tissue planes

Localized cortical and Single or multiple

medullary abscesses radiolucent cortical or

medullary lesions with surrounding sclerosis Deprivation of blood supply Sequestration

to cortex due to thrombosis

of metaphyseal vessels and

interruption of periosteal

vessels, cortical necrosis

External migration of dead Sinus tracts

pieces of cortex with

breakdown of skin and

subcutaneous tissue

implicated The importance of osteomyelitis of the

mandible and maxilla in persons with poor dental

hygiene and of the frontal portion of the skull and face in

persons with chronic sinusitis is undeniable Soft tissue

infections that lead to bone and joint contamination are

frequent after trauma, animal and human bites, puncture

wounds, irradiation, burns, and decubitus or pressure

ulcers in paralyzed or immobilized patients

General Radiographic and Pathologic Features

Whereas the direction of contamination in

hematoge-nous osteomyelitis is from the bone outward into the soft

tissue, the direction of contamination in osteomyelitis

resulting from adjacent sepsis is from the soft tissues

inward into the bone (or joint) (Table 53–4; Fig 53–11)

Periosteal bone formation is commonly the initial

radio-graphic manifestation of osteomyelitis After traumatic

initiation of soft tissue infection, periostitis may appear

early in response to injury and may not reflect actual

bone infection With further accumulation of pus,

sub-periosteal resorption of bone and cortical disruption

ensue As infection gains access to the spongiosa, it may

spread in the marrow, producing lytic osseous defects on

the radiograph

Specific Locations

Hand. Three distinct routes are available to organisms

that become lodged in the soft tissues of the hand;

infec-tion may disseminate via tendon sheaths, fascial planes,

or lymphatics (Fig 53–12) Infective digital tenosynovitis

can result from a puncture wound, particularly in a flexor

crease of the finger, where skin and sheath are intimately

related A sheath infection may perforate into an adjacent

bone or joint in the finger; the most characteristic site of

such extension is the proximal interphalangeal

articula-tions and adjacent middle phalanx (Fig 53–13) The

metacarpophalangeal joints are altered less commonly.Such tenosynovitis causes exquisite tenderness over thecourse of the sheath, a semiflexed position of the finger,severe pain on extension of the finger, and fusiformswelling of the digit

Infections in the fascial planes of the hand are numerousbut result in joint or bone alterations less frequently than

do those in the synovial sheaths Lymphangitis may resultfrom superficial injuries In intense cases, complicationsmay include tenosynovitis, septicemia, osteomyelitis, andseptic arthritis

A

B

Figure 53–8. Brodie’s abscess: radiographic abnormalities.

Tibial metaphyseal involvement in a 19-year-old woman.

Routine radiograph shows a metaphyseal radiolucent lesion

(arrow) with a medial channel (arrowheads) (Courtesy of M.

Mitchell, MD, Halifax, Nova Scotia, Canada.)

Figure 53–9. Chronic osteomyelitis: sequestration A, In this

radiograph of a femur, chronic osteomyelitis is associated with

several radiodense, sharply marginated foci (arrows) within lucent cavities that contain granulation tissue B, CT scanning identifies sequestered bone (arrow).

A felon results from infection in the terminal pulp

space Bone involvement is not infrequent in neglected

cases because of the close proximity of the terminal phalanx

(Fig 53–14) Subcuticular abscesses of the nail fold are

termed paronychia On rare occasions, osseous

destruc-tion of a terminal phalanx may be evident (Fig 53–15)

Foot. The plantar aspect of the foot is especially able to soft tissue infection Foreign bodies, puncturewounds, or skin ulceration from weight bearing canrepresent the portal of entry for various organisms In adiabetic patient, soft tissue breakdown over certain pres-sure points (e.g., metatarsal heads, calcaneus) leads toinfection that is combined with vascular and neurologicabnormalities

vulner-Puncture wounds of the plantar aspect of the foot canlead to osteomyelitis and septic arthritis (Fig 53–16) Theinfective organisms can vary, but gram-negative agents

such as Pseudomonas aeruginosa are frequently implicated;

this is not surprising, because these organisms are usuallyfound in the soil and may be normal inhabitants of skin.Typically, local pain and swelling appear within days after

a puncture wound, although radiographs usually arenormal at this time After a delay of 1 to 3 weeks, theradiographs reveal typical abnormalities of osteomyelitis

or septic arthritis Osteomyelitis of the os calcis is arecognized complication of repeated heel punctures inneonates

The clinical, radiographic, and pathologic istics of osteomyelitis (and septic arthritis) complicatingfoot infections in diabetic patients are modified by theassociated problems of these persons, including vascularinsufficiency and neurologic deficit The radiographicpicture usually reveals significant soft tissue swelling andmottled osteolysis (Fig 53–17) Osteosclerosis, fragmen-tation, periostitis, and soft tissue gas may be seen Insome diabetic patients with foot infections complicated

character-by osteomyelitis, findings can simulate those of diabeticneuropathic osteoarthropathy, and differentiation ofneurologic and infectious processes can be difficult Infact, both infection and neuropathic osteoarthropathy ofthe midfoot and forefoot frequently coexist in diabeticpatients

Pelvis. Soft tissue breakdown that occurs in debilitatedpersons who maintain a single position for long periods

is referred to as a pressure sore, decubitus ulcer, orbedsore Although other sites (e.g., heels) may beaffected, most pressure sores develop about the pelvis,

Figure 53–10. Chronic sclerosing osteomyelitis Chronic

osteomyelitis can be associated with considerable new bone

formation In this patient, a cortical abscess contains a

sequestrum (arrow) and is surrounded by sclerosis (arrowheads).

The appearance is reminiscent of that of an osteoid osteoma.

Figure 53–11. Diagrammatic representation of the

sequen-tial steps of osteomyelitis resulting from a contiguous

contami-nated source 1, Initially, a soft tissue focus of infection is

apparent Occasionally, such a focus can irritate the underlying

bone, producing periostitis without definite invasion of the cortex.

2, The infection subsequently invades the cortex, spreading via

haversian and Volkmann’s canals 3, Finally, the medullary bone

and marrow spaces are affected.

TABLE 53–4

Osteomyelitis Due to Spread from a Contiguous Source

of Infection: Radiographic-Pathologic Correlation

Pathologic Abnormality Radiographic Abnormality

Soft tissue contamination and Soft tissue swelling, mass abscess formation formation, obliteration

of tissue planes Infectious invasion of the Periostitis periosteum with lifting of the

membrane and bone formation Subperiosteal abscess formation Cortical erosion and cortical invasion

Infection in haversian and Cortical lucency and Volkmann’s canals of cortex destruction Contamination and spread in Bone lysis marrow

especially near the sacrum, ischial tuberosities,

trochan-teric regions, and buttocks Local soft tissue infection

and bacteremia are commonly associated with decubitus

ulcers Osteomyelitis is observed most commonly in the

innominate bones and proximal portions of the femora,areas subjacent to sites of skin breakdown, and is related

to spread from a contiguous contaminated source.The accurate diagnosis of osteomyelitis complicatingpressure sores is difficult, owing to a number of otherconditions that may become evident in immobilized orparalyzed patients Pressure-related changes in bone arenot infrequent, leading to flattening and sclerosis of bony

Figure 53–12. Spread of infection in the hand: available anatomic pathways A, Drawing demonstrates the

relationships of the tendon sheaths, bursae, and fascial planes (thenar space, midpalmar space) B, Drawing

of a section through the metacarpal bones outlines two spaces—the midpalmar and thenar spaces—

separated by a septum and located above the digital flexor tendon sheaths Note the close relationship

between the sheath of the index finger and the thenar space and between the sheaths of the third, fourth,

and fifth fingers and the midpalmar space (From Resnick D: Osteomyelitis and septic arthritis complicating

hand injuries and infections: Pathogenesis of roentgenographic abnormalities J Can Assoc Radiol 27:21,

1976.)

Figure 53–13. Spread of infection in the hand: digital flexor

tenosynovitis After a neglected puncture wound, a 45-year-old

woman developed tenosynovitis and osteomyelitis Note the

soft tissue swelling, particularly along the volar surface of the

proximal phalanx (open arrow); the semiflexed position of the

finger; and extensive permeative osseous destruction, with

pathologic fracture (solid arrow) of the proximal phalanx (From

Resnick D: Osteomyelitis and septic arthritis complicating

hand injuries and infections: Pathogenesis of roentgenographic

abnormalities J Can Assoc Radiol 27:21, 1976.)

Figure 53–14. Spread of infection in the hand: felon An infection in the pulp space has produced considerable soft tissue

swelling (open arrows) Extension into the tuft and diaphysis of the terminal phalanx is apparent (solid arrows) Shrapnel from a

previous injury can be seen (From Resnick D: Osteomyelitis and septic arthritis complicating hand injuries and infections: Pathogenesis of roentgenographic abnormalities J Can Assoc Radiol 27:21, 1976.)

prominences such as the femoral trochanters and ischial

tuberosities Heterotopic ossification, a well-recognized

accompaniment of neurologic injury, further complicates

the early diagnosis of osteomyelitis Routine radiography

is reported to be insensitive and nonspecific in the

diagnosis of bone infection in patients with pressuresores, related in part to the difficulty of differentiatingchanges caused by abnormal pressure from those ofosteomyelitis CT and MR imaging are helpful, althoughprecise diagnosis frequently requires histologic examina-tion of the bone

Direct Implantation of Infection

General Clinical Features

Puncture wounds of the hand and foot can lead toosteomyelitis (and septic arthritis) by contamination ofadjacent soft tissues or by direct inoculation of the bone

or joint This latter complication is especially prevalent

in the foot, where nails, splinters, or glass can lead todeep puncture wounds; in the hand, where a human bitereceived during a fistfight can directly injure osseous andarticular structures; and in any site after an animal bite

General Radiographic Features

The features of bone (and joint) involvement after directimplantation of an infectious process are virtuallyidentical to those occurring after spread of infection from

a contiguous contaminated source Commonly, osseousdestruction and proliferation lead to focal areas of lysis,sclerosis, and periostitis Soft tissue swelling is common,related not to infection but to edema resulting from theinjury itself

Figure 53–15. Spread of infection in the hand: paronychia.

Widespread infection of the pulp space, digital flexor tendon

sheath, terminal tuft, and distal interphalangeal joint (solid

arrows) resulted from an initial subcuticular abscess Soft tissue

swelling along the tendon sheath can be noted (open arrows).

(From Resnick D: Osteomyelitis and septic arthritis

compli-cating hand injuries and infections: Pathogenesis of

roentgeno-graphic abnormalities J Can Assoc Radiol 27:21, 1976.)

Figure 53–16. Spread of infection in the foot: puncture wounds.

After a puncture wound from a nail, this patient developed a

plantar soft tissue infection that led to osteomyelitis and septic

arthritis Observe osseous destruction of the metatarsal head and

proximal phalanx, joint space narrowing, and soft tissue swelling.

Figure 53–17. Spread of infection in the foot: diabetes mellitus Radiograph reveals a soft tissue infection about the first metatarsophalangeal joint, with ulcerations and erosion of bone

(arrowheads) Observe vascular calcification and alterations at

the second metatarsophalangeal joint.

Human Bites

The most common cause of human bite injury is a fist

blow to the mouth that results in laceration of the

dorsum of the metacarpophalangeal joint Joint infection

is more common than bone infection in these cases S.

aureus or Streptococcus species are the usual implicated

organisms The radiographic findings, which are

particu-larly well shown on steep oblique and lateral radiographs,

include peculiar bony defects and fractures, tooth

frag-ments, and osseous and articular destruction (Fig 53–18)

Animal Bites

Superficial animal bites or scratches can inoculate local

soft tissues, leading to infection of underlying bones and

joints Deep animal bites can introduce organisms

directly into osseous and articular structures Dog bites

account for approximately 90% of these injuries and cat

bites for about 10% Approximately 5% of dog bites and

20% to 50% of cat bites become infected significantly

The infecting organisms vary, but Pasteurella multocida is

commonly implicated, especially in cat bites Any anatomic

site can be affected, although animal bites are seen

pre-dominantly in the hand, arm, and leg (Fig 53–19)

Open Fractures and Dislocations

Whenever a fracture or dislocation is complicated bydisruption of the overlying skin, direct inoculation ofbones and joints can occur This problem is especiallyrelevant to injuries of the tibia Despite the earlyadministration of antibiotics, chronic osteomyelitis isfrequent in this setting

Postoperative InfectionPostoperative infections occur as a result of contamina-tion of bones and joints from adjacent infected softtissues, direct inoculation of osseous and articular tissue

at the time of surgery, or, less frequently, hematogenousspread to an operative site from a distant location.Particularly troublesome are instances of infection thatoccur after internal fixation of fractures, intervertebraldisc surgery, median sternotomy, and various types of

Figure 53–18. Infection due to direct implantation: human

bites Destruction of the third metacarpal head (solid arrow) and

a narrowed metacarpophalangeal joint (open arrow) resulted

from infection after a fistfight in which the patient’s fist struck

the opponent’s teeth (From Resnick D: Osteomyelitis and

septic arthritis complicating hand injuries and infections:

Pathogenesis of roentgenographic abnormalities J Can Assoc

Radiol 27:21, 1976.)

Figure 53–19. Infection due to direct implantation: animal

bites A, After a cat bite, this patient developed Pasteurella

osteomyelitis and septic arthritis Observe soft tissue swelling, osseous destruction of the proximal and middle phalanges, and joint space narrowing and flexion at the proximal interpha-

langeal joint B, In a different patient who developed Pasteurella

osteomyelitis and septic arthritis after a cat bite, a coronal weighted (TR/TE, 800/20) spin echo MR image obtained with fat saturation technique and intravenous gadolinium enhance- ment shows high signal intensity in the third metacarpo- phalangeal joint and adjacent bone and soft tissue.

T1-reconstructive procedures and arthroplasty One or more

organisms may be implicated; S aureus is the most

com-mon pathogen

One special type of postoperative infection relates to

the transcutaneous insertion of pins into bone The

causative organisms vary, but infections caused by

gram-negative bacteria are common The mechanisms of

contamination are also variable; in some cases, the pins

are inserted into bones that are already the site of

osteomyelitis, whereas in others, osseous infection occurs

at the time of or after pin insertion Radiographs reveal

progressive osteolysis about the metal or, after removal of

the pin, a ring sequestrum (Fig 53–20) In the latter

instance, the central circular radiolucent area created by

the pin itself is surrounded by a ring of bone, which, in

turn, is surrounded by an area of osteolysis

Complications

Severe Osteolysis. If osteomyelitis is not treated

ade-quately or early enough, severe osteolysis may ensue

Large foci of destruction eventually can lead to

disap-pearance of long segments of tubular or flat bones

Epiphyseal Growth Disturbance. Injury to the cartilage cells

on the epiphyseal side of the growth plate is irreparable,

and subsequent growth disturbances are to be expected

Even with severe epiphyseal disintegration, however,

some regeneration of the epiphysis can occur after

eradication of the infection (Fig 53–21) It is difficult to

predict the occurrence and extent of epiphyseal recovery

after injury

Neoplasm. Epidermoid carcinoma arising in a focus of

chronic osteomyelitis is not uncommon The latent period

between the onset of osteomyelitis and the appearance

of neoplasm is variable, although a time span of 20 to

30 years is typical Neoplasm most frequently arises cent to the femur and the tibia and is clinically evident

adja-as pain, increadja-asing drainage, hemorrhage, onset of a foulodor from the sinus tract, a mass, and lymphadenopathy.Radiographically, there is progressive destruction of bone(Fig 53–22) The prognosis is guarded

Amyloidosis. Secondary amyloidosis can complicatechronic osteomyelitis This complication has become lessfrequent, however, owing to improvement in the chemo-therapy of infection It is seen in less than 5% of cases ofchronic osteomyelitis

Modifications and Diagnostic Difficulties

Antibiotic-Modified Osteomyelitis. The previous sion was concerned with the radiographic and pathologicfindings of untreated osteomyelitis During the earlyhealing phase of osteomyelitis, bone resorption continues

discus-as damaged osseous tissue is removed Therefore,radiographically evident increased destruction can occur

at a time when the clinical picture is improving

Active and Inactive Chronic Osteomyelitis. Differentiation

of active and inactive chronic osteomyelitis by imagingtechniques can be extremely difficult, but certain indica-tions on the radiograph may be helpful (Table 53–5)

Figure 53–20. Postoperative infection: pinhole ring

sequestrum Percutaneous pins were used to treat a fracture

about the wrist in this 27-year-old man Purulent drainage

occurred, requiring removal of the pins Note the classic

radiographic findings of a ring sequestrum (arrow).

Figure 53–21. Complications of osteomyelitis: epiphyseal destruction This 11-year-old boy developed osteomyelitis and septic arthritis of the first metatarsophalangeal joint One week after initial presentation, the epiphysis has fragmented and largely disappeared, and osteolysis of both the metatarsal bone and the phalanx can be noted Joint space narrowing is seen (Courtesy of T Goergen, MD, Escondido, Calif.)

Periostitis that is thin and linear in quality and separated

from the subjacent bone suggests activity Poorly defined

or fluffy periosteal excrescences extending into the

adja-cent soft tissues also suggest active infection Finally,

documentation of an abscess or sequestration on routine

radiography, conventional tomography, CT, or MR

imag-ing implies activity, because necrotic osseous fragments

or abscesses commonly harbor viable organisms

Differential Diagnosis

General Features. The combination of clinical and imaging

characteristics in osteomyelitis usually ensures the correct

diagnosis Occasionally, aggressive bone destruction

com-bined with periostitis and soft tissue swelling simulates

the changes in malignant neoplasms, especially Ewing’s

sarcoma or osteosarcoma in children, histiocytic lymphoma

in young adults, and skeletal metastasis in older persons

The imaging features of osteomyelitis may resemble those

of bone infarction, especially in the diaphysis of a long

bone Further, patients who have sickle cell anemia orGaucher’s disease, and those who have lymphoprolifer-ative disorders or are receiving steroid medications, arepredisposed to the development of either osteomyelitis

or bone infarction (or both), compounding the diagnosticdifficulty

Periostitis. The nature of the periosteal proliferationaccompanying osteomyelitis is varied In some patients,single or multiple osseous shells appear This “onion-skinning” is not specific for osteomyelitis, because it mayalso be evident in malignant neoplasm (e.g., Ewing’ssarcoma) A triangular area (Codman’s triangle) ofperiostitis, similar to that seen in osteosarcoma, may beevident in osteomyelitis In cases of osteomyelitis inwhich a single thick layer of periosteal bone is seen, thechanges are reminiscent of eosinophilic granuloma ortraumatic periostitis

Osteolytic Foci. In a child, identification of a metaphysealradiolucent lesion abutting the growth plate or connect-

ed to it by a channel suggests the presence of an abscess.Although osteosarcoma is typically metaphyseal in loca-tion, and Ewing’s sarcoma may be metaphyseal, the os-teolytic foci in these tumors are more poorly marginated,and considerable neoplastic bone production may beevident in osteosarcoma In a child, epiphyseal infectionwith abscess formation leads to radiographic featuressimilar to those of chondroblastoma, enchondroma, oreosinophilic granuloma

Osteosclerosis. In some cases of osteomyelitis, exuberantbone formation produces widespread sclerosis This may

be uniform or combined with mottled radiolucent shadows.The resulting radiographic picture can simulate malig-nant bone tumors (e.g., osteosarcoma, Ewing’s sarcoma,histiocytic lymphoma, chondrosarcoma), osteonecrosis,fibrous dysplasia, or Paget’s disease

Sequestration. Radiodense foci representing sequestra arereliable indicators of infection Their occasional appear-ance in tumors (e.g., fibrosarcoma) does not significantlydiminish the diagnostic nature of the finding

Soft Tissue Masses and Swelling. In general, tumors areassociated with circumscribed soft tissue masses thatdisplace surrounding soft tissue planes and frequentlycontain visible tumor matrix Infections lead to infiltra-tion and obscureness of soft tissue planes This differen-tiation is not uniformly reliable, however

Figure 53–22. Complications of osteomyelitis: neoplasm.

This 69-year-old man developed a squamous cell carcinoma of

a sinus tract after years of osteomyelitis of the tibia with

drainage A, Lateral radiograph shows osteolysis of the tibia,

which was related to tumorous involvement of the bone A soft

tissue mass at this site cannot be seen in this image The soft

tissue mass and involved bone were excised B, In the immediate

postoperative period, a sagittal fat-suppressed T1-weighted

(TR/TE, 550/20) spin echo MR image obtained after

intra-venous gadolinium contrast agent administration shows edema

of high signal intensity in the tibia, presumably related to the

surgery, although the presence of residual intraosseous tumor

could not be excluded.

TABLE 53–5

Radiographic Signs of Activity in Chronic Osteomyelitis

Change from previous radiograph Poorly defined areas of osteolysis Thin, linear periostitis

Sequestration

SEPTIC ARTHRITIS

Articular Manifestations of Infection

Septic arthritis is but one of several processes that can

cause or perpetuate articular disease in patients with

infection An infectious agent may trigger a sterile

syn-ovitis at a site distant from the primary infective focus A

classic example is the reactive arthritis of acute rheumatic

fever occurring as a complication of streptococcal throat

infection Clinical characteristics common to reactive

arthritides include a symptom-free interval, a self-limited

course in which cartilage or bone destruction is rare, a

characteristic clinical presentation that includes acute

migratory polyarthritis, a tendency in some patients

toward involvement of the heart, and a negative serologic

test for rheumatoid factor Inciting infections commonly

reach the body through one of three portals of entry: the

oronasopharynx and respiratory tract, the urogenital

tract, and the intestinal tract The existence of reactive

arthritis in patients with infection underscores the

impor-tance of performing joint aspiration and attempting to

isolate the causative organisms in all cases of suspected

septic arthritis

Routes of Contamination

The potential routes of contamination of joints can be

divided into the same categories used in the previous

discussion of osteomyelitis (Fig 53–23)

1 Hematogenous spread of infection Hematogenous

seed-ing of the synovial membrane results from either direct

transport of organisms within the synovial vessels or

spread from an adjacent epiphyseal focus of osteomyelitis

by means of vascular continuity between the epiphysis

and the synovial membrane

2 Spread from a contiguous source of infection A joint may

become contaminated by intra-articular extension of

osteomyelitis from an epiphyseal or metaphyseal focus

or of neighboring suppurative soft tissue processes

3 Direct implantation Inoculation of a joint can occur

during aspiration or arthrography or after a penetrating

wound

4 Postoperative infection An intra-articular suppurative

process can occur after arthroscopy or any other type

of joint surgery

Hematogenous Infection

Pathogenesis

Hematogenous spread of infection to a joint indicates

that organisms are transported within the vasculature of

the synovial membrane directly from a distant infected

source or indirectly from an adjacent bone infection In

either case, infection of the synovial membrane precedes

contamination of the synovial fluid Therefore, initial

arthrocentesis may suggest bland inflammation of the

joint The reaction of the synovial tissue to the contained

organisms varies according to the local and general

resistance of the patient and the number, type, and

viru-lence of the infecting agents

General Clinical Features

Monoarticular involvement is the major pattern ofpresentation, especially in younger age groups Thespecific site or sites of infection depend on the age of thepatient, the organism, and the existence of an underlyingdisease or problem The knee, particularly in children,infants, and adults, and the hip, especially in children andinfants, are frequently affected With pyogenic infection,

an acute onset with fever and chills is typical, although aprodromal phase of several days’ duration with malaise,arthralgia, and low-grade fever can be encountered Pain,tenderness, redness, heat, and soft tissue swelling of theinvolved joint are common Leukocytosis and positiveblood and joint cultures are important laboratory par-ameters of pyogenic arthritis Elevated erythrocyte sedi-mentation rates and C-reactive protein levels are alsoencountered The organism most commonly implicated

is S aureus H influenzae represents an important and

common cause of septic arthritis in children youngerthan 5 years

Radiographic-Pathologic Correlation

In response to bacterial infection, the synovial membranebecomes edematous, swollen, and hypertrophied Increasedamounts of synovial fluid are produced; the fluid may

be thin and cloudy, contain large numbers of leukocytes,and reveal a lowered sugar level and an elevated proteincount After a few days, frank pus accumulates in thearticular cavity, and destruction of cartilage begins (Table53–6; Fig 53–24) Prominent abnormality may appear atthe margins or in central portions of joints, accompanied

by growth of the inflamed synovium across the surface ofthe cartilage or between cartilage and bone Cartilaginouserosion (from superficially located pannus) and disrup-tion of the chondral surface (from subchondral pannus)can develop With further fluid, the capsule becomesdistended, surrounding soft tissue edema is evident, andosseous abnormalities ensue Superficial marginal andcentral bony erosions may progress to extensive destruc-tion of large segments of the articular surface Fibrous orbony ankylosis can eventually occur

Radiographic abnormalities parallel the pathologicchanges in pyogenic arthritis (Fig 53–25) Interosseousspace narrowing, which is frequently diffuse, reflectsdamage and disruption of the chondral surface Osseouserosions at the edges of the joint, related to the effects ofdiseased synovium on bone, lead to marginal defects.Subchondral extension of pannus destroys the bone plateand adjacent trabeculae, leading to poorly defined gaps inthe subchondral “white” line on the radiograph Furtherdestruction of bone becomes evident, and in late stages,bony ankylosis of the joint may be seen

Rapid destruction of bone and cartilage is istic of bacterial arthritis, whereas in tuberculosis andfungal diseases articular changes occur more slowly Intuberculosis, marginal osseous erosions with preservation

character-of joint space and periarticular osteoporosis may beprominent Infrequently, gas formation within a jointcomplicates septic arthritis Much more frequently, theappearance of radiolucent collections in an infected jointindicates that a prior arthrocentesis has been performed

A B

Figure 53–23. Septic arthritis: potential routes of contamination A, Hematogenous spread of infection

to a joint can result from direct lodgment of organisms in the synovial membrane (1) Spread into the joint from a contiguous source can occur from a metaphyseal focus that extends into the epiphysis and from there into the joint (2), from a metaphyseal focus with extension into the joint when the growth plate is intra- articular (3), or from a contiguous soft tissue infection (4) Direct implantation after a penetrating wound

(5) can also lead to septic arthritis B, Hematogenous spread of infection to a joint can occur owing to

vascular continuity between the epiphysis and the synovial membrane The vessels shown include arterioles (1), venules (2), and capillaries (3) of the capsule; periosteal vessels (4); the nutrient artery (5); and

metaphyseal-epiphyseal anastomoses (6) C, Sequence of events by which the synovial membrane can become infected from an osseous focus before the joint fluid is contaminated D, Spread from a contiguous

osseous surface can result from penetration of the cartilage (1) or pathologic fracture with articular contamination (2) In this situation, synovial fluid may become infected before the synovial membrane.

Infection from a Contiguous Source

Pathogenesis

In certain age groups, osteomyelitis can be complicated

by contamination of the adjacent articulation Septic

arthritis complicating osteomyelitis occurs in as many as

one third of patients and is seen most commonly in the

hip and knee In infants, the presence of vascular

commu-nication between metaphyseal and epiphyseal segments

of tubular bones allows organisms within nutrient vessels

to localize in the epiphysis and subsequently extend into

the joint In adults, vascular connections between the

epiphysis and metaphysis are reestablished as the growth

plate closes Hematogenous osteomyelitis thus can affectthe epiphysis in this age group

A second situation in which septic arthritis can occur

as a result of contamination from a contiguous source

is related to adjacent soft tissue infection or, moreinfrequently, nearby visceral infection (e.g., vesicoace-tabular or enteroacetabular fistulas) Predisposing factorsinclude pelvic trauma, surgical manipulation, anddiverticulitis

Joint infection may also develop as a result of sion from a surrounding suppurative process in sites

exten-TABLE 53–6

Septic Arthritis: Radiographic-Pathologic Correlation

Pathologic Abnormality Radiographic Abnormality

Edema and hypertrophy of Joint effusion, soft tissue

synovial membrane with swelling

BA

Figure 53–24. Septic arthritis: pathologic abnormalities 1,

Normal synovial joint 2, An edematous, swollen, and

hyper-trophic synovial membrane becomes evident 3 and 4,

Accumu-lating inflammatory pannus leads to chondral destruction and

to marginal and central osseous erosions 5, Bony ankylosis may

eventually result.

Figure 53–25. Septic arthritis: hematogenous spread of

infection A, Radiograph reveals joint space narrowing and

osseous erosions, which predominate at the margins of the talus

(arrows) B, In this patient with acquired immunodeficiency

syndrome, a sagittal STIR (TR/TE, 3200/18; inversion time,

150 msec) MR image show classic features of septic arthritis of the ankle, with cartilage and bone erosion and marrow edema

in the tibia and talus.

where the growth plate has an intra-articular location;

the most important such sites are the hip and the

gleno-humeral joint Because of this anatomic arrangement,

osteomyelitis localized to the metaphysis can enter the

joint by extending laterally without violating the growth

plate

Radiographic-Pathologic Correlation

Usually, radiographic evidence exists that the infective

process originates outside the articulation This evidence

may include soft tissue deficit, swelling, or gas

forma-tion; osteomyelitis with typical epiphyseal or

metaphy-seal destruction; and diverticulitis or cystitis with

fistulization In certain situations, however, joint effusion

and cartilaginous and subchondral osseous destruction are

the first radiographic clues to infection Once the

articu-lation has been violated, the radiographic and pathologic

abnormalities of the infection are virtually identical to

those associated with hematogenously derived

suppura-tive joint disease

Specific Entities

Neonatal septic arthritis affects the hip joint most

fre-quently, and S aureus is the organism most commonly

implicated In this age group, infection can reach the hip

via spread from a metaphyseal focus of osteomyelitis either

directly into the joint (the growth plate is intra-articular)

or to the epiphysis by way of vascular channels that cross

the growth plate Clinically, infants with septic arthritis

of the hip may manifest irritability, loss of appetite, and

fever Initial radiographs of the hip are frequently

unre-markable With accumulation of intra-articular fluid,

pathologic subluxation or dislocation of the femoral head

can occur, although the lack of ossification in most of

the proximal capital femoral epiphysis makes this sign

difficult to apply (Fig 53–26) A helpful finding,

how-ever, is radiographically detectable osteomyelitis of the

femoral metaphysis manifested as osteolysis,

osteoscle-rosis, or periostitis

The radiographic findings of hip infection in infants

can simulate those of other conditions; therefore,

aspiration of the joint is mandatory to firmly establish the

diagnosis of septic arthritis and to provide guidelines for

adequate therapy Only as the child develops and

ossification of the immature skeleton proceeds will the

degree of residual deformity from destruction of the

cartilaginous femoral head and acetabulum become

apparent (Fig 53–27)

Septic arthritis of the hip is also frequent in children,

although the overall frequency of this problem and the

extent of its devastating effects on local cartilage and

bone are less than in infants It may be associated with

the acute onset of fever, pain, swelling, and limping, as

well as a dramatic leukocytosis On radiographs,

accumulation of intra-articular fluid may produce soft

tissue swelling, capsular distention, and subtle lateral

displacement of the ossified epiphysis The prognosis of

septic arthritis of the hip for a child is far better than that

for an infant Osteonecrosis of the femoral head

occurring after metaphyseal or epiphyseal infection in a

child (or infant) is an important complication of thedisease (Fig 53–28) Osteonecrosis of the epiphysis isusually not recognized until 6 to 8 weeks after the onset

of infection The epiphysis can reveal a generalizedincrease in radiodensity, followed by fragmentation and,less commonly, collapse

Direct Implantation of InfectionArthrocentesis for the evaluation of synovial contents

or for arthrography can introduce gram-positive orgram-negative bacteria Similarly, penetrating injuries,such as those that occur in a fistfight or from a bullet,knife, nail, or other sharp object, can lead to septicarthritis

Postoperative InfectionArticular surgery in the form of arthroscopy, arthrotomy,arthrodesis, arthroplasty, or another procedure can becomplicated by joint infection in the postoperativeperiod Infections occurring soon after such proceduresare usually related to direct inoculation of the jointduring the operation or to intra-articular spread from anadjacent contaminated focus (e.g., soft tissue abscess).Joint infection occurring long after surgery is frequentlyassociated with obvious preceding sepsis elsewhere in thebody and may relate to hematogenous spread to the jointfrom this distant process

Figure 53–26. Septic arthritis of the hip: infancy This infant developed septic arthritis of the right hip and osteomyelitis Note displacement of the “capsular” and obturator fat planes

(solid arrows), obliteration of the iliopsoas fat plane (arrowhead),

and a metaphyseal focus of infection (open arrow) The

femoral head is displaced laterally and is slightly enlarged The soft tissue findings indicative of intra-articular fluid may be of more diagnostic help in this age group than in adults (Courtesy of J Weston, MD, Lower Hutt, New Zealand.)

Several potential complications of septic arthritis deserve

emphasis The frequency of synovial cyst formation in

septic arthritis appears to be low Infrequently, synovial

rupture of the cyst, with or without sinus tract formation,

is observed Septic arthritis can lead to disruption of

adjacent capsular, tendinous, and soft tissue structures.This complication has been well documented in theglenohumeral joint

Radiographic and pathologic evidence of osteomyelitis

is associated with septic arthritis Bony abnormalitiescan antedate and be the source of the suppurative jointprocess, or they can indicate the contamination of adja-cent bony surfaces from a primary joint infection Partial

or complete osseous fusion may represent the residualfindings of septic arthritis This complication is not fre-quent; however, bone ankylosis is occasionally encoun-tered after pyogenic processes Significant destruction ofarticular cartilage from joint sepsis can lead to incon-gruity of apposing articular surfaces and, later, to changes

of secondary osteoarthritis The resulting radiographicfindings, consisting of joint space narrowing, sclerosis,and osteophytosis, may be difficult to differentiate fromprimary osteoarthritis

Modifications and Diagnostic DifficultiesInadequate or inappropriate administration of antibioticscan modify articular infection Clinical manifestationsmay be masked, appearing relatively late in the course

of the disease, and radiographic changes may be lessdramatic, less extensive, and much delayed When infec-tion is superimposed on a previous articular disordersuch as rheumatoid arthritis, calcium pyrophosphatedihydrate crystal deposition disease, or osteoarthritis, theclinical and radiographic abnormalities can be hidden orchanged by the underlying disease process

Differential DiagnosisAlthough numerous disorders such as pigmented villo-nodular synovitis, idiopathic synovial osteochondromato-

Figure 53–28. Septic arthritis of the hip: childhood The

complication of osteonecrosis in a child with septic arthritis of

the hip is well demonstrated in this patient Subsequently,

pro-gressive osteomyelitis and septic arthritis produced increased

intra-articular fluid and osteonecrosis of the femoral head,

manifested as increased radiodensity Eventually, disintegration

of the femoral head occurred.

Figure 53–27. Septic arthritis of the hip: infancy A, This neonate developed septic arthritis of the right

hip The initial radiograph reveals soft tissue swelling and periosteal reaction along the femur (arrowhead).

B, At age 13 years, the ossification centers of the greater and lesser trochanters are apparent Femoral

dislocation, acetabular shallowness, and absence of epiphyseal ossification are evident (From Freiberger

RH, Ghelman B, Kaye JJ, and Spragge JW: Hip disease of infancy and childhood In Moseley RD Jr, et al

[eds]: Current Problems in Radiology Chicago, Year Book Medical Publishers, 1973.)

sis, juvenile chronic arthritis, and even adult-onset

rheumatoid arthritis can be associated with

mono-articular changes, infection must be considered the prime

diagnostic possibility until proved otherwise This is

particularly true when the joint process is associated with

loss of interosseous space, poorly defined or “fuzzy”

osseous margins, and a sizable effusion In patients with

pyogenic infection, the articular destruction can be rapid

Diagnostic difficulty arises when the septic process

involves more than one joint or when septic arthritis

appears during the course of another articular disorder

Of all the radiographic features of infection, it is the

poorly defined nature of the bony destruction that is

most characteristic Osseous erosions or cysts in gout,

rheumatoid arthritis, seronegative spondyloarthropathies,

osteoarthritis, pigmented villonodular synovitis, idiopathic

synovial osteochondromatosis, hemophilia, and calcium

pyrophosphate dihydrate crystal deposition disease are

more sharply marginated Further, concentric loss of

interosseous space is typical in infection, but focal

diminution of the articular space (as noted in

osteo-arthritis) and relative preservation of articular space (as

seen in gout, pigmented villonodular synovitis, idiopathic

synovial osteochondromatosis, and hemophilia) are rare

in pyogenic infection

Marginal erosions are frequent in processes associated

with significant synovial inflammation, such as sepsis,

rheumatoid arthritis, and the seronegative

spondylo-arthropathies They may also be observed in gout and,

less commonly, in pigmented villonodular synovitis and

idiopathic synovial osteochondromatosis Similarly,

peri-articular osteoporosis can be encountered in rheumatoid

arthritis, Reiter’s syndrome, juvenile chronic arthritis,

hemophilia, and nonpyogenic suppurative processes,

such as tuberculosis or fungal disease Intra-articular

bony ankylosis can represent the end stage of septic

arthritis, the seronegative spondyloarthropathies, and, in

some locations, rheumatoid arthritis and juvenile chronic

arthritis

SOFT TISSUE INFECTION

Routes of Contamination

Infection of soft tissue structures commonly results from

direct contamination after trauma Any process that

disrupts the skin surface can lead to secondary infection

Hematogenous spread is less important as a mechanism

in soft tissue contamination than it is in osteomyelitis and

septic arthritis

Radiographic-Pathologic Correlation

Swelling with obliteration of adjacent tissue planes is

characteristic of soft tissue infection Radiolucent streaks

within the contaminated area can relate to collections of

air derived from the adjacent skin surface or to gas

formation by various bacteria (Fig 53–29) Erosion of

bone due to pressure from an adjacent soft tissue mass is

much more frequent when the mass is neoplastic rather

than infectious in origin When osseous abnormalities

appear after soft tissue contamination, infective

perios-titis, osteitis, or osteomyelitis is usually present (Fig.53–30) A well-defined soft tissue mass is less typical ofinfection than of neoplasm The edema of an infectiousprocess usually leads to infiltration of surrounding softtissues rather than displacement

Specific Entities

Septic Subcutaneous Bursitis. Septic bursitis most quently localizes to the olecranon and the prepatellarand, less frequently, the subdeltoid regions A history ofrecent injury, occupational trauma, or puncture is fre-quently, though not invariably, present Clinical manifes-tations include painful swelling localized to the involvedbursa, subcutaneous edema, a normal range of jointmotion, and fever Routine radiography, bursography, or

fre-MR imaging (Fig 53–31) may be used to define theextent of the soft tissue infection Septic bursitis is usuallynot associated with infectious arthritis

Septic Tenosynovitis. Septic processes originating from adistant or local focus or occurring after trauma can alsolead to tenosynovitis Soft tissue swelling and surfaceresorption and erosion of underlying bony structures may

be evident MR imaging (Fig 53–32) and phy are appropriate diagnostic methods applied to theassessment of suppurative tenosynovitis

ultrasonogra-Figure 53–29. Soft tissue infection: gas formation Escherichia

coli infection in diabetes mellitus Note the “bubbly”

radiolu-cent collections in the foot.

Lymphadenitis. Lymphadenitis, usually with an panying cellulitis, can complicate streptococcal orstaphylococcal infections Nodular or diffuse soft tissueswelling and underlying periostitis may be encountered.Cat-scratch disease often manifests in this fashion.

Figure 53–31. Septic olecranon bursitis Note olecranon

swelling (arrows) and soft tissue edema due to Staphylococcus

aureus Previous surgery and trauma are the causes of the

adjacent bony abnormalities.

Figure 53–32. Infective tenosynovitis and cellulitis: extensor tendons of wrist and fingers In this 50-year-old man with a puncture wound on the dorsum of the hand, a transverse intermediate-weighted (TR/TE, 2000/43) spin echo MR image shows infection involving the subcutaneous soft tissues and peritendinous tissue of the second finger.

Figure 53–30. Soft tissue infection: myelitis This 30-year-old man developed a soft

osteo-tissue infection after an injury A, Radiograph

shows soft tissue swelling and bone erosion in

the middle phalanx (arrow) B, Coronal

fat-suppressed fast spin echo (TR/TE, 2000/21)

MR image confirms the presence of litis with bone erosion and edema and a soft tissue infective focus manifested as a region of high signal intensity.

osteomye-Cellulitis. Cellulitis represents an acute inflammatory

process of the deeper subcutaneous tissue; involvement

of deep fasciae and muscles is unusual in cases of

uncom-plicated cellulitis Clinical findings include pain or

tender-ness, redtender-ness, swelling, warmth, and mild to moderate

fever Cellulitis generally results from a streptococcal or,

less commonly, a staphylococcal infection Radiographic

findings are nonspecific and are usually confined to the

soft tissues With T2-weighted spin echo MR imaging,

cellulitis is characterized by subcutaneous thickening and

hyperintense streaks or fluid collections in the

subcu-taneous fat and superficial fascial tissues Enhancement

of signal intensity in these regions is evident when

gadolinium-containing contrast agents are administered

intravenously (see Fig 53–32)

Necrotizing Fasciitis. Necrotizing fasciitis represents a

rare type of soft tissue infection that is accompanied by

widespread fascial necrosis in the absence of muscular or

cutaneous infection It is a serious condition associated

with systemic toxicity and, if untreated, death Routine

radiography may reveal evidence of soft tissue gas, although

the clinical findings of fever, pain, swelling, and bullae

usually allow an accurate diagnosis MR imaging shows

involvement of both superficial and deep soft tissue

structures; the demonstration of deep fasciae with fluid

collections, thickening, and enhancement of signal

inten-sity with intravenous gadolinium-containing contrast

agents generally distinguishes this condition from

cellulitis (Fig 53–33)

Infectious Myositis. Inflammation of muscle may occur in

a variety of infectious disorders caused by viruses, bacteria,

protozoa, and parasites Pyogenic myositis (pyomyositis)

is a well-recognized and serious infection affecting children

and young adults in tropical regions (tropical

pyomyosi-tis) and, less frequently, in other locations Although the

disease, as described classically, occurs in otherwise healthy

persons, it is being recognized with increasing frequency

in malnourished and immunodeficient patients

Pyomyosi-tis is related to S aureus infection in about 90% of cases

(streptococci account for most of the remaining cases)

Sonographically guided percutaneous drainage may be

helpful in the diagnosis and management of the

condi-tion, and MR imaging may further delineate the location

and extent of the disease process MR imaging findings

(Fig 53–34) include muscle enlargement; abscesses

characterized by a peripheral rim of increased signal

intensity on T1-weighted spin echo MR images, a central

region (representing fluid) of intense signal on

T2-weighted images, and peripheral enhancement after

intravenous administration of gadolinium-based contrast

medium; and associated abnormalities of subcutaneous

edema in some cases

SPECIFIC SITUATIONS

Chronic Granulomatous Disease

This heterogeneous disorder is a hereditary condition,

usually transmitted as an X-linked recessive trait, that

occurs in male children, although a similar syndrome has

been identified in female and male children without afamily history of disease The syndrome is characterized

by purulent granulomatous and eczematoid skin lesions,granulomatous lymphadenitis with suppuration, hepato-splenomegaly, recurrent and persistent pneumonias, andchronic osteomyelitis (25% to 35%) It is frequently fatal(40%), and death before adolescence is common Virtu-ally every organ or tissue is vulnerable to infection in thisdisorder Histologically, granulomas composed primarily

of plasma cells, lymphocytes, macrophages, and nucleated giant cells, with or without central caseation,are seen A defect has been noted in the ability of thepolymorphonuclear leukocytes and monocytes to destroycertain pathogenetic organisms adequately Certainclinical and radiographic peculiarities characterize theosteomyelitis of chronic granulomatous disease ofchildhood:

multi-1 The disease lacks the usual early clinical signs andsymptoms of osteomyelitis, so that initial radiographsfrequently reveal considerable bony involvement

2 The causative organisms are usually of low virulence

3 The most frequent site of involvement is the smallbones of the hands and feet

4 Osteomyelitis may result either from contaminationrelated to an adjacent focus of infection, especially inthe thoracic region, or from hematogenous dissemi-nation

5 The radiographic abnormalities are characterized byextensive osseous destruction with minimal reactivesclerosis

Figure 53–33. Necrotizing fasciitis and myositis with abscess formation and fistula: thigh After the intravenous adminis- tration of a gadolinium-containing contrast agent, a transverse T1-weighted (TR/TE, 400/15) spin echo MR image reveals

peripheral enhancement (arrows), consistent with an abscess.

Note the presence of the fistula (From Rahmouni A, Chosidow

O, Mathieu D, et al: MR imaging in acute infectious cellulitis Radiology 192:493, 1994.)

6 Osteomyelitis may develop in new areas despite

con-tinuous therapy

7 Osteomyelitis eventually responds to long-term

anti-biotic therapy, so operative intervention is seldom

necessary

Chronic Recurrent Multifocal Osteomyelitis

Chronic recurrent multifocal osteomyelitis (CRMO),

which is also discussed as part of the SAPHO (synovitis,

acne, pustulosis, hyperostosis, osteitis) syndrome in

Chapter 82, is a variety of subacute and chronic

osteomyelitis of unknown cause that occurs in childhood

and frequently causes multiple and symmetrical

altera-tions It has also been referred to as condensing osteitis

of the clavicle in childhood, chronic symmetrical plasma

cell osteomyelitis, chronic sclerosing osteomyelitis, and

multifocal chronic osteomyelitis The usual age of onset

of the disease is 5 to 10 years, although infants and adults

may be affected Skin lesions, including pustulosis palmaris

et plantaris, acne fulminans, and psoriasis, are observed

in some patients CRMO has also been associated with

Wegener’s granulomatosis, inflammatory bowel disease,

and leukemia The metaphyses of the bones of the lower

extremity and the medial ends of the clavicles are

particu-larly vulnerable Osteolysis with intense sclerosis may

be noted In certain locations, such as the clavicle, the

bone may become massive (Fig 53–35) The dominant

radiographic feature at any skeletal site is bone sclerosis

(Fig 53–36) This feature is similar or identical to that

described in cases of Garré’s sclerosing osteomyelitis

Both bone scintigraphy and MR imaging can be used

to detect skeletal lesions in CRMO With the former

method, diagnostic difficulty is sometimes encountered

owing to the normal uptake of radionuclide in the

Figure 53–34. Infective myositis: soleus muscle Staphylococcus aureus infection in a 34-year-old patient

with acquired immunodeficiency syndrome A, On a transaxial T1-weighted (TR/TE, 500/30) spin echo

MR image, a rim of increased signal intensity (arrow) is evident B, With T2 weighting (TR/TE, 2000/90),

a similar transaxial image shows a central area of marked hyperintensity surrounded by a hypointense band

(arrow), which is itself surrounded by a more diffuse region of hyperintensity The MR imaging findings are

those of an abscess (From Fleckenstein JL, Burn DK, Murphy FK, et al: Differential diagnosis of bacterial

myositis in AIDS: Evaluation with MR imaging Radiology 179:653, 1991.)

Figure 53–35. Chronic recurrent multifocal osteomyelitis: clavicle Note massive enlargement of the clavicle Biopsy and histologic evaluation indicated only chronic osteitis Cultures were negative (Courtesy of G Greenway, MD, Dallas, Tex.)

Figure 53–36. Chronic recurrent multifocal osteomyelitis: pelvis Transaxial CT scan shows diffuse sclerosis of the ilium Note that the sacrum is unaffected (Courtesy of M Pathria,

MD, San Diego, Calif.)

physeal region of tubular bones With MR imaging, low

signal intensity in affected regions is seen on

T1-weighted spin echo images, and variable signal intensity

is noted on T2-weighted images Laboratory analysis is

usually nonspecific, and cultures of blood or bone after

biopsy may be nonrewarding Although the long-term

prognosis is good, the condition may run a protracted

course with resultant skeletal deformities

Of considerable interest, the selective hyperostosis of

the clavicle in this condition may also be seen in two

other disorders Osteitis condensans (condensing osteitis)

of the medial end of the bone has been reported,

espe-cially in young women (see Chapter 47)

Sternocosto-clavicular hyperostosis of unknown cause, with painful

swelling of the sternum, clavicles, and upper ribs, has also

been described Men and women are both affected, and

the usual age at onset is in the fifth or sixth decade of life

Sternocostoclavicular hyperostosis is discussed further in

Chapter 82 The relationship of CRMO to these other

conditions is not clear, although the common

involve-ment of the clavicle, as well as several other features,

suggests an association

Osteomyelitis and Septic Arthritis

in Intravenous Drug Abusers

An increased frequency of infectious disease has been

noted in intravenous drug abusers The mechanisms for

this association are not entirely known Use of

contami-nated narcotics or needles, colonization of the skin during

previous hospitalizations, and alterations of the bacterial

flora by pretreatment with antibiotics are three potential

mechanisms that may explain an increased frequency of

infection in intravenous drug abusers

Hematogenous osteomyelitis and septic arthritis in

intra-venous drug users are characterized by unusual localization

and unusual organisms Although staphylococcal infection

may be seen, Pseudomonas, Klebsiella, and Serratia are

com-monly implicated The axial skeleton is frequently

affect-ed, especially the spine, sacroiliac joint, and sternoclavicular

joint, with less common involvement of the

manubrioster-nal joint (Fig 53–37) The precise cause of axial skeletal

involvement in intravenous drug abusers is not clear

The occurrence of systemic candidiasis in heroin

addicts deserves emphasis Contamination of the lemon

used to dissolve “brown” heroin by strains of Candida

albicans previously colonizing the oropharynx and skin of

heroin addicts is probably the source of the infection

Musculoskeletal sites of involvement include, foremost,

the costochondral joints and, less commonly, the spine,

sacroiliac joints, knees, and wrists Additional

musculo-skeletal manifestations in intravenous drug abusers include

lymphedema, thrombophlebitis, subcutaneous fat necrosis,

atrophy and calcification, pyomyositis, myonecrosis,

teno-synovitis, and chemical inflammation of the synovium

due to direct intra-articular administration of the drug

OTHER DIAGNOSTIC TECHNIQUES

Computed Tomography

The primary applications of CT to the evaluation of

musculoskeletal infections are the delineation of the

osseous and soft tissue extent of the disease process,especially in areas of complex anatomy such as the verte-bral column, and the monitoring of percutaneous aspira-tion and biopsy procedures, particularly of the spine,retroperitoneal tissues, and sacroiliac joints

Many of the CT abnormalities in osteomyelitis areshared by primary and secondary malignant neoplasmsaffecting the skeleton, including an increased attenuationvalue in the medullary canal, destruction of cortical bone,new bone formation, and a soft tissue mass With CTscanning, the detection of gas within the medullary canal

is an infrequent but reliable diagnostic sign of litis that may not be as evident on radiographs or MRimaging (Fig 53–38); it is analogous to the presence ofgas within soft tissue abscesses Fat-fluid levels within the

osteomye-Figure 53–37. Hematogenous osteomyelitis and septic arthritis in an intravenous drug abuser: sacroiliac joint Note indistinct margins about a narrowed sacroiliac joint.

Figure 53–38. Acute osteomyelitis: CT In this 54-year-old

man with Enterobacter osteomyelitis of the hip and femur,

transaxial CT scan at the level of the proximal portion of the

femur reveals intramedullary gas collections (arrow) (Courtesy

of V Vint, MD, San Diego, Calif.)

medullary canal or in the adjacent joint are also reported

in osteomyelitis and septic arthritis CT evaluation in

patients with subacute or chronic osteomyelitis may reveal

cortical sequestration, cloacae, and bone and soft tissue

abscesses (Fig 53–39)

Sinography

Retrograde injection of contrast material defines the

course and extent of the sinus tract and its possible

com-munication with an underlying bone or joint Sinography

may be combined with CT scanning or MR imaging for

better delineation of the sinus tracts

Arthrography

The principal reason for performing a joint puncture in

the clinical setting of infection is to obtain fluid for

bacteriologic examination After removal of the joint

contents, however, contrast opacification of the joint can

be used to outline the extent of the synovial inflammation

and the presence of capsular, tendinous, and soft tissue

injury

Ultrasonography

Ultrasonography is a useful technique for detecting

effu-sions in the hip in children with transient synovitis, septic

arthritis, or Legg-Calvé-Perthes disease The absence of

joint fluid in this joint on sonographic examination

excludes the diagnosis of septic arthritis, though it does

not eliminate the possibility of osteomyelitis Further,

sonography can be used to monitor aspiration of the

effusion Ultrasonography can also be employed in the

detection of joint fluid in adults with septic arthritis of

the hip and, in a similar fashion, to assess the presence

and extent of infected fluid in superficially located joints,

synovial cysts, bursae, and tendon sheaths in both children

and adults

Radionuclide Examination

Although the use of scintigraphy in the evaluation of

musculoskeletal infections is discussed in Chapter 7, a

few comments are appropriate here Technetium

phos-phate bone scans become abnormal within hours to days

after the onset of bone infection and days to weeks before

the disease becomes manifest on conventional radiographs

The scintigraphic abnormality initially may be evident as

Figure 53–39. Chronic osteomyelitis: CT Transverse CT scan reveals bone destruction and a sequestrum in the calcaneus that resulted from a pin tract infection.

a photo-deficient area (“cold” spot), a finding that isrelated to fulminant infection with thrombosis or vas-cular compression; within a few days, however, increasedaccumulation of the radioisotope (“hot” spot) is typical(Fig 53–40) The bone scan can also be used to monitorthe disease course and response to treatment, althoughseveral weeks may be required before the scan returns tonormal, and the correlation between clinical and scinti-graphic improvement is not uniformly good Occasionaldifficulty in interpreting the bone scan in younger patientsarises from an inability to differentiate between normaland abnormal activity in the metaphyseal region

A gallium scan can be performed in conjunction with

a technetium scan in the same patient, and the resultinginformation may be more useful than that obtained byeither examination alone (Table 53–7; see Fig 53–40).Gallium scans may reveal abnormal accumulation inpatients with active osteomyelitis when technetium scansreveal decreased activity (cold lesions) or perhaps normalactivity (transition period between cold and hot lesions)

It should be remembered that gallium is a bone scanningagent that accumulates in regions of increased boneremodeling, such as occur in osteomyelitis Therefore, itsaccumulation in osseous sites that are also positive ontechnetium phosphate scans is not unexpected, and suchaccumulation by itself does not increase the specificity ofthe radionuclide examination Rather, when both tech-

TABLE 53–7

Radionuclide Evaluation of Osseous and Soft Tissue Infection

Technetium phosphates Early scans show increased Early and late scans show increased Scans may remain positive,

uptake; later scans are uptake (scans in early acute even in inactive disease normal osteomyelitis may reveal “cold” spots)

active disease

netium phosphate and gallium scanning are used, it is

important to compare the degree and extent of

radio-nuclide uptake on the two examinations Disparate

distri-bution of uptake or increased intensity of uptake on the

gallium study is an important sign of osteomyelitis Such

infection is unlikely when both technetium phosphate and

gallium scanning are negative or when the distribution of

both tracers is spatially congruent and the relative

inten-sity of gallium uptake is less than that of the bone tracer

Although a negative delayed bone image appears to be

specific in excluding infection, a positive finding during

the delayed static phase of the examination lacks

speci-ficity for infection and has stimulated considerable interest

in “three-phase” examinations in patients with

musculo-skeletal infection This encompasses serial images obtained

during the first minute after a bolus injection of a

tech-netium compound (angiographic phase), a postinjection

image obtained at the end of the first minute or after

several minutes (blood pool phase), and additional images

obtained 2 or 3 hours later (delayed phase) If increased

accumulation of radionuclide within bone is observed in

all three phases, the diagnosis of osteomyelitis is highly

likely Conversely, if such an increase is present only

on the delayed image, an alternative diagnosis should be

considered Soft tissue infections are characterized by

delayed images that either are normal or reveal

mini-mally increased tracer accumulation within the bone,

presumably because of regional hyperemia Septic

arthri-tis is usually accompanied by increased uptake of the

radiopharmaceutical agent in juxta-articular bone in the

delayed images, moderate and diffuse blood pool hyperemia,

and, on the radionuclide angiogram, increased flow to

the joint space (Fig 53–41) The addition of a fourth

phase to the scintigraphic examination, representing astatic image obtained 24 hours after injection of the bone-seeking radiopharmaceutical agent, may help in thisdifferentiation Advantages of the 24-hour image relate

to continued accumulation of the technetium phosphate

Figure 53–40. Soft tissue infection: imaging findings This 37-year-old man, with a history of chronic

inactive osteomyelitis of the proximal portion of the radius, developed a staphylococcal soft tissue infection.

A, Radiograph shows soft tissue swelling and osseous deformity of the proximal portion of the radius and

ulna B, Technetium phosphate bone scan reveals accentuated uptake of the radiopharmaceutical agent

(arrows) in the humerus, radius, and ulna about the elbow C, Gallium scan indicates abnormality of soft

tissue alone (arrow) (Courtesy of V Vint, MD, San Diego, Calif.)

A

B

C

D

Figure 53–41. Septic arthritis: bone scanning A to C,

Three-phase technetium phosphate study documents increased flow

(arrow) in the angiographic phase (A), diffuse hyperemia about

the hip (arrow) in the blood pool stage (B), and increased uptake

of the radiopharmaceutical agent (arrow) in the delayed image

(C) These findings indicate septic arthritis D, Gallium scan is

also abnormal, with increased scintigraphic activity about the

hip (arrow) (Courtesy of G Greenway, MD, Dallas, Tex.)

radionuclide in the abnormal woven bone about foci of

infection

The accumulation of leukocytes at sites of abscess

for-mation has led to the use of indium-labeled autologous

leukocytes for the evaluation of inflammatory processes

In general, 111In-labeled leukocyte scintigraphy is less

sensitive in detecting bone infections than soft tissue

infections and leads to difficulty in differentiating

osteo-myelitis and septic arthritis It can demonstrate soft tissue

extension from an area of bone infection Positive

leuko-cyte images are encountered in musculoskeletal

condi-tions other than infection Rheumatoid arthritis and other

synovial inflammatory disorders can lead to findings

simu-lating those of septic arthritis, and primary or secondary

tumors in the soft tissue or bone can produce positive

leukocyte images similar to those accompanying

infec-tion Compared with bone imaging with 99mTc

com-pounds, 111In scintigraphy has increased sensitivity in the

detection of early osteomyelitis

Magnetic Resonance Imaging

Acute osteomyelitis typically appears as an area of low

signal intensity on T1-weighted spin echo MR images

and high signal intensity on T2-weighted images, its

con-spicuity being influenced by the hematopoietic or fatty

nature of the adjacent marrow (Fig 53–42) The process

of subacute and chronic osteomyelitis has a more variable

MR imaging appearance, although in cases of chronic

active infection, similar characteristics of signal

inten-sity are observed Additional MR imaging

abnormal-ities in either acute or chronic osteomyelitis include

cortical erosion or perforation, periosteal bone

forma-tion, soft tissue involvement, and, in chronic

osteo-myelitis, abscesses, bone sequestration, and sinus tracts

With short tau inversion recovery (STIR) imaging,

osteomyelitis and soft tissue infection appear as areas of

markedly increased signal intensity that are reportedly

more conspicuous than on routine spin echo MR images

(Fig 53–43)

After intravenous administration of a gadolinium

con-trast agent, areas of vascularized inflammatory tissue

reveal enhancement of signal intensity, but

nonvascu-larized abscess collections show either no enhancement

or enhancement at the margin of the lesion Brodie’s

abscesses (Fig 53–44) typically appear as well-defined

intraosseous regions of low signal intensity on T1-weighted

spin echo MR images (with a rim of intermediate signal

intensity related to a layer of highly vascularized

granu-lation tissue, termed the penumbra sign, surrounded by a

variable amount of low signal intensity related to marrow

edema) and as areas of high signal intensity on

T2-weighted spin echo MR images (with a rim of low signal

intensity due to sclerotic bone surrounded by a variable

amount of high signal intensity related to marrow

edema); they may be better delineated with

gadolinium-enhanced MR imaging

Sequestra, although better seen on CT scans, appear

as regions of low to intermediate signal intensity on both

T1- and T2-weighted images and do not show

enhance-ment of signal intensity after intravenous administration

of a gadolinium-based contrast agent The inflamed

synovial membrane in cases of septic arthritis, as inrheumatoid arthritis, is enhanced after the intravenousinjection of a gadolinium agent

Although numerous reviews have emphasized thesensitivity of MR imaging in the diagnosis of muscu-loskeletal infections, it is this very sensitivity that can lead

to diagnostic problems, particularly in defining theextent of the process Several specific problem areas can

be defined:

1 In acute osteomyelitis, differentiating soft tissue sion of infection from soft tissue edema or differen-tiating osteomyelitis from surrounding intraosseousreactive edema

exten-2 In septic arthritis, differentiating secondary osteomyelitisfrom bone marrow edema; or in acute osteomyelitis

A

B

Figure 53–42. Acute osteomyelitis: MR imaging A, Coronal

T1-weighted (TR/TE, 650/20) spin echo MR image shows a long segment of abnormal bone marrow manifested as a region

of low signal intensity B, Transaxial T2-weighted (TR/TE,

2000/80) spin echo MR image shows that the infection, demonstrating high signal intensity, has extended from the marrow through the posterior cortex into the soft tissues Documentation of the extent of the soft tissue infection, which requires its differentiation from edema, is difficult (Courtesy of

G Greenway, MD, Dallas, Tex.)

affecting epiphyses, differentiating secondary septic

arthritis from sympathetic effusions

3 In chronic osteomyelitis, differentiating active and

inactive disease

Figure 53–43. Septic arthritis and osteomyelitis: MR

imaging A, Coronal T1-weighted (TR/TE, 350/20) spin echo

MR image displays the infectious process in this 75-year-old

woman as areas of low signal intensity in the proximal end of

the right femur and adjacent acetabulum A joint effusion of low

signal intensity is evident B, Coronal STIR (TR/TE, 2700/30;

inversion time, 160 msec) image better delineates the bone and

soft tissue abnormalities, which are of high signal intensity.

Although extremely sensitive in the documentation of

inflam-mation, STIR imaging can lead to an overestimation of the

extent of the process (Courtesy of M Pathria, MD, and D.

Bates, MD, San Diego, Calif.)

Figure 53–44. Brodie’s abscess: MR imaging In a sagittal T1-weighted (TR/TE, 567/20) spin echo MR image, the wall

of the abscess in the distal metaphysis of the tibia has

intermediate signal intensity (arrow), the penumbra sign Note

surrounding marrow edema of low signal intensity (Courtesy

of D Goodwin, MD, Hanover, N.H.)

Figure 53–45. Diabetic foot infection: MR imaging This 63-year-old man required amputation of the

third toe at the level of the metatarsophalangeal joint for control of infection He later developed clinical

manifestations of recurrent infection A, Transverse T1-weighted (TR/TE, 700/15) spin echo MR image

shows abnormally low signal intensity in the third and fourth metatarsal bones (arrows) and in the adjacent

soft tissues The head of the second metatarsal bone also appears to be involved B, Transverse STIR

(TR/TE, 1800/25; inversion time, 160 msec) image reveals high signal intensity in these metatarsal bones

(arrows) and soft tissues C, Transverse T1-weighted (TR/TE, 900/13) fat-suppressed image obtained in

conjunction with intravenous administration of gadolinium contrast agent provides information similar to

that in (B) A third and fourth ray resection confirmed the presence of osteomyelitis.

740

4 In soft tissue infections, differentiating infective

perios-titis, osteitis, or osteomyelitis from bone marrow edema

The assessment of infection in the feet of diabetic

patients provides unique challenges (Fig 53–45) Although

reported data indicate the value of scintigraphic methods,

particularly 111In-labeled leukocyte imaging with or

with-out bone scintigraphy, the day-to-day clinical experience

of many physicians suggests otherwise A normal bone

scan virtually excludes the presence of osteomyelitis,

neuropathic osteoarthropathy, or both The hyperemia

associated with either process can lead to positive results

with three-phase bone scintigraphy Decreased blood flow

and possible impaired leukocyte responsiveness limit the

sensitivity achievable with 111In-labeled leukocyte

scin-tigraphy in diabetic foot infections; however, reports

indicate that the finding of definite increased uptake on

leukocyte scans has a high positive predictive value, and

the absence of increased leukocyte uptake in or near bone

makes the diagnosis of osteomyelitis very unlikely

Although high signal intensity in the bone marrow on

T2-weighted spin echo and STIR images and on

T1-weighted spin echo MR images (with or without fat

saturation) after the intravenous administration of

gado-linium contrast agent is compatible with the diagnosis of

osteomyelitis, it is not a specific finding (see Fig 53–43)

Neuropathic osteoarthropathy in the absence of

coexis-tent infection is accompanied by persiscoexis-tent low signal

intensity in the bone marrow on T2-weighted spin echo

MR images, although this is not a constant finding In

rapidly developing neuropathic osteoarthropathy, acute

fragmentation of bone is associated with marrow edema,

resulting in high signal intensity on T2-weighted spin

echo and STIR images and those images obtained after

the intravenous administration of a gadolinium-containing

contrast agent (Fig 53–46) With application of the last

of these methods, the presence of soft tissue or osseous

abscesses suggests that the accompanying marrow

altera-Figure 53–46. Diabetic neuropathic osteoarthropathy and osteomyelitis: MR imaging Transverse STIR (TR/TE, 1800/20; inversion time, 125 msec) MR image shows high signal inten- sity in the marrow of the second and third metatarsal bones, in the intermediate and lateral cuneiform bones, and in the soft tissues Note the neuropathic changes about the first tarso-

metatarsal joint (arrow) and a Lisfranc pattern of subluxation

(arrowhead) In such cases, it is difficult to differentiate sites of

osteomyelitis from neuropathic disease with marrow edema.

TABLE 53–8

Some Useful MR Imaging Protocols in Assessment of

Musculoskeletal Infections

Condition Suggested Protocols

Osteomyelitis in red T2-weighted spin echo

marrow T1-weighted spin echo with

gadolinium contrast enhancement STIR

Osteomyelitis in yellow T1-weighted spin echo

marrow T1-weighted spin echo with

gadolinium contrast enhancement and fat suppression

STIR Septic arthritis T1-weighted spin echo with

gadolinium contrast enhancement with or without fat suppression Soft tissue infection T1-weighted spin echo with

gadolinium contrast enhancement with or without fat suppression

STIR, short tau inversion recovery.

tions are related to osteomyelitis rather than to pathic osteoarthropathy Some guidelines for this choice

neuro-in cases of osteomyelitis, septic arthritis, and soft tissueinfections are provided in Table 53–8

FURTHER READINGAzouz EM: Computed tomography in bone and joint infec- tions J Can Assoc Radiol 32:102, 1981.

Bonakdar-pour A, Gaines VD: The radiology of osteomyelitis Orthop Clin North Am 14:21, 1983.

Boutin RD, Resnick D: The SAPHO syndrome: An evolving concept for unifying several idiopathic disorders of bone and skin AJR Am J Roentgenol 170:585, 1998.

Bressler EL, Conway JJ, Weiss SC: Neonatal osteomyelitis examined by bone scintigraphy Radiology 152:685, 1984 Butt WP: The radiology of infection Clin Orthop 96:20, 1973 Butt WP: Radiology of the infected joint Clin Orthop 96:136, 1973.

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Osteomyelitis, Septic Arthritis,

and Soft Tissue Infection:

Axial Skeleton

SUMMARY OF KEY FEATURES

The routes of contamination of the spine, the sacroiliac

joint, and other axial skeletal sites are identical to those

of the appendicular skeleton In the spine, early loss

of intervertebral disc space is characteristic of pyogenic

infection and is associated with lysis and sclerosis of

neighboring bone These findings can simulate those

of other disorders, such as rheumatoid arthritis,

intervertebral (osteo)chondrosis, and conditions

complicated by cartilaginous node formation Sacroiliac

joint infection is typically unilateral in distribution,

a feature that allows its differentiation from many

other articular processes Additional locations in the

axial skeleton are not uncommonly infected in

intravenous drug abusers and in patients after trauma,

surgery, or diagnostic and therapeutic procedures

INTRODUCTION

The distribution of osteomyelitis and septic arthritis is

dramatically influenced by the age of the patient, the

specific causative organism, and the presence or absence

of any underlying disorder or situation In children and

infants, frequent involvement of the bones and joints of

the appendicular skeleton is evident, whereas in adults,

localization of infection to the osseous and articular

structures of the vertebral column is common Spinal

infection is also frequent in intravenous drug abusers and

in patients with tuberculosis

SPINAL INFECTIONS

Routes of Contamination

Hematogenous Spread of Infection. Hematogenous spread

through arterial and venous routes (Batson’s paravertebral

venous system) can result in lodgment of organisms in

the bone marrow of the vertebrae This vascular

arrange-ment allows two direct routes for the hematogenous

spread of infection: via the nutrient arteries and via the

paravertebral venous system Although the contribution

of each system to cases of spinal osteomyelitis is a matter

of debate, it is attractive to implicate the valveless venous

plexus—whose direction and extent of flow are

dramati-cally influenced by changes in abdominal pressure—in

the frequent spread of infection (and neoplasm) to the

spine from pelvic sources (Fig 54–1) Urinary tract

infec-tions or surgery, rectosigmoid disease and enteric fistulas,

and septic abortion or postpartum infection are

well-recognized pelvic precursors of vertebral osteomyelitis.The common localization of early foci of osteomyelitis inthe subchondral region of the vertebral body, an arearichly supplied by nutrient arterioles, emphasizes thatarterial rather than venous pathways may be more impor-tant in hematogenous osteomyelitis of the spine

The role of hematogenous spread of infection directlyinto the intervertebral disc has stimulated great interest

It has been suggested that in children and adolescentsyounger than 19 or 20 years, vascular channels perforatethe vertebral endplate and allow organisms in the blood-stream to have direct access to the intervertebral disc.This concept has led to the application of such popularterms as “discitis.” A similar occurrence in adults hasbeen attributed to a persistent disc blood supply or to asupply that has been reinstated by vascular invasion ofdegenerating disc tissue

Spread from a Contiguous Source of Infection.Vertebral orintervertebral disc infection can result from contamina-tion by an adjacent soft tissue suppurative focus Even incases in which bone or cartilage involvement follows softtissue infection, it is extremely difficult to eliminate thepossibility that osteomyelitis or disc infection is a result

of hematogenous or lymphatic seeding Tuberculous andfungal infection, however, can extend from the spine tothe neighboring tissue, dissect along the subligamentousareas for a considerable distance, and then reenter thevertebral body or intervertebral disc Further, cases ofosteomyelitis and infective discitis have been reported as

a complication of colonic, hypopharyngeal, and esophagealperforation or instrumentation In all these examples,however, the role of bacteremia with subsequent hema-togenous seeding of the spine must be considered

A specific entity that may be related to this mechanism

of infection is Grisel’s syndrome, in which spontaneousatlantoaxial subluxation accompanies inflammation ofneighboring soft tissues, mainly in children (Fig 54–2).Proposed causes of this phenomenon include musclespasm, ligamentous laxity, and synovial effusion; the directcontinuity of the periodontoidal venous plexus and thesuboccipital epidural sinuses with the pharyngovertebralveins suggests the existence of a hematogenous route forthe transport of peripharyngeal septic exudates to theupper cervical spine structures

Direct Implantation. Organisms can be directly implantedinto the intervertebral disc (and, far less commonly, thevertebra) during attempted puncture of the spinal canal,intervertebral disc, paravertebral and peridural tissues, oraorta, or in penetrating injuries Usually, the interver-tebral disc is the initial site of infection, especially in cases

of misguided puncture, and the vertebra becomes taminated as a secondary event

con-Postoperative Infection. The more frequent and sive spinal operations that are currently being undertaken

743

have led to an increase in postoperative infection of thespinal column Laminectomy, discectomy, instrumenta-tion, and fusion can each be complicated by osteomyelitis

or disc infection The localization of osseous or articularcontamination depends on the precipitating surgical event.Clinical Abnormalities

The reported frequency of osteomyelitis and disc spaceinfection (together termed infective spondylitis) has risendramatically Initially, infective spondylitis was thought

to represent less than 1% of all cases of osteomyelitis;now it appears that 2% to 4% is a more accurate esti-mate Men are affected more commonly than women.The highest frequency of septic spondylitis occurs in thefifth and sixth decades of life The lumbar spine is themost typical site of involvement, followed by the thoracicspine; sacral and cervical abnormalities occur with aboutequal frequency The usual location of infection in thevertebra is the vertebral body

A history of recent primary infection, instrumentation,

or a diagnostic, therapeutic, or surgical procedure is mon The most frequently encountered (55% to 90%)

pyogenic organism is Staphylococcus aureus or, less monly, Staphylococcus epidermidis, although other gram-

com-positive and, less typically, gram-negative agents may beimplicated Clinical manifestations vary with the virulence

of the organism and the nature of the host’s resistance.General findings include fever, malaise, anorexia, andweight loss Back pain is a common initial local manifes-tation and may be intermittent or constant, exacerbated

by motion, and throbbing at rest With accompanyingsoft tissue abscess formation, hip contracture can occur(psoas muscle irritation) Appropriate culture of theblood can identify the causative organism in some cases,although more drastic methods, such as needle biopsy oraspiration, may be necessary

A

B

C

Figure 54–1. Anatomic considerations: Batson’s

paraverte-bral venous system This valveless, plexiform set of veins lies

outside the thoracoabdominal cavity and anastomoses with the

cavitary veins at each segmental level Thus, communication

exists between the pelvic and vertebral venous system, femoral

and iliac veins, inferior and superior venae cavae, and other

important venous structures 1, paravertebral venous plexus; 2,

inferior vena cava; 3, inferior mesenteric vein; 4, internal iliac

vein; 5, pelvic plexus (Modified from Vider M, Maruyama Y,

Narvaez R: Significance of the vertebral venous (Batson’s) plexus

in metastatic spread in colorectal carcinoma Cancer 40:67,

1977.)

Figure 54–2. Grisel’s syndrome.

A head tilt developed in this year-old boy after an ear infec-

11-tion A, Scout view from a CT

study reveals deviation of the

head to the left side B, Transaxial

CT scan at the level of the atlas shows that it is rotated about the odontoid process, with the right side of the atlas located anterior

to the left side C, Transaxial

T1-weighted (TR/TE, 300/15) spin echo MR image obtained after the intravenous injection of a gado- linium contrast agent reveals a similar position of the atlas, which

is rotated with respect to the axis The adjacent soft tissues show some degree of hyperintensity because of gadolinium enhance- ment The rotational abnormality resolved slowly over a period of months (Courtesy of S Wall,

MD, San Francisco, Calif.)

combination of rapid loss of intervertebral disc heightand adjacent lysis of bone is most suggestive of an infec-tious process Such involvement of two contiguous ver-tebral bodies is almost uniformly associated with trans-discal infection and is rarely the result of multicentricinvolvement.

Later Abnormalities. After a variable period (10 to 12 weeks),regenerative changes manifesting as sclerosis or ebur-nation appear in the bone The osteosclerotic response is

Radiographic-Pathologic Correlation

Early Abnormalities. Hematogenous spread of infection

frequently leads to a focus in the anterior subchondral

regions of the vertebral body adjacent to the

interver-tebral disc (Fig 54–3) Disc perforation soon ensues At

this stage, radiographs may be entirely normal Soon

(1 to 3 weeks), however, decrease in intervertebral disc

height is accompanied by loss of normal definition of the

subchondral bone plate and enlarging destructive foci

within the neighboring vertebral body (Fig 54–4) The

Figure 54–3. Spinal infection: sequential stages A, An anterior subchondral focus in the vertebral body

is typical B, Infection may then perforate the vertebral surface and reach the intervertebral disc space C,

With further spread of infection, contamination of the adjacent vertebral body and narrowing of the

intervertebral disc space are recognizable D, With continued dissemination, infection may spread in a

subligamentous fashion and erode the anterior surface of the vertebral body (arrowhead) or perforate the

anterior ligamentous structures (arrow).

Figure 54–4. Spinal infection: early and later radiographic abnormalities A, Observe the loss of definition

of the superior aspect of a lumbar vertebral body (arrowheads), with narrowing of the adjacent intervertebral

disc space This appearance (in a middle-aged man with pyogenic infection) conforms to the stage in Figure

54–3B B, In this young child, a staphylococcal infection has led to destruction of two adjacent vertebral

bodies (arrowheads) and narrowing of the intervening intervertebral disc A soft tissue mass is apparent This

appearance corresponds to the stage in Figure 54–3D.

variable in severity and has been used in the past as a

helpful sign in differentiating pyogenic from tuberculous

infection Although such sclerosis is indeed common in

pyogenic (nontuberculous) spondylitis, it may also be

evi-dent in tuberculosis More helpful in this differentiation

is a combination of findings that strongly indicates

tuber-culous spondylitis, including the presence of a slowly

progressive vertebral process with preservation of

inter-vertebral discs, subligamentous spread of infection with

erosion of the anterior vertebral margins, large and

calci-fied soft tissue abscesses, and the absence of severe bony

eburnation (Fig 54–5)

In the lumbar spine, such extension can lead to

oblit-eration or displacement of the psoas margin; in the

thoracic spine, a paraspinal mass can be encountered; and

in the cervical spine, retropharyngeal swelling can lead to

displacement and obliteration of adjacent prevertebral fat

planes With early and proper treatment, reconstitution

can result, with production of a radiodense (ivory)

ver-tebra, a relatively intact or ankylosed intervertebral disc,

and surrounding osteophytosis (Fig 54–6)

Special Types of Spinal Infection

Most infections of the intervertebral disc occur as an

extension of vertebral osteomyelitis or direct inoculation

during diagnostic or surgical procedures In children,

however, a hematogenous route to the disc still exists,

and hematogenous contamination of disc tissue is

pos-sible Clinical symptoms and signs may become evident

between 1 and 16 years of age (average age,

approxi-mately 5 years), and a preexisting infectious condition

(upper respiratory tract, urinary tract, or ear infection) isusually apparent Manifestations are generally mild andinclude back pain, abdominal pain, hip irritability, andaltered gait Low-grade fever, irritability, malaise, eleva-tion of the erythrocyte sedimentation rate, and, on occa-sion, leukocytosis are noted in many cases When positive,

blood or bone biopsy culture most typically reveals S.

aureus Negative culture results are reported in 50% to

90% of cases

Scintigraphy may reveal increased accumulation ofbone-seeking pharmaceuticals at a relatively early stage.Intervertebral disc space narrowing is later accompanied

by erosion of the subchondral bone plate and osseouseburnation (Fig 54–7) Magnetic resonance (MR) imag-ing in cases of childhood discitis reveals findings similar

to those in adults with infective spondylitis

Other Diagnostic TechniquesThe role of radionuclide studies in establishing the pres-ence of spinal infection at a stage when radiographs areentirely normal is well documented Technetium-,gallium-, and indium-labeled radiopharmaceutical agentscan be used in this regard The application of pinholescintigraphy and single photon emission computedtomography (SPECT) has further increased thesensitivity of bone scanning in the diagnosis of infectivespondylitis

Computed tomography (CT) scanning allows tion of the extent of osseous and disc destruction andparavertebral and intraspinal involvement (Fig 54–8).The intravenous injection of contrast material aids in the

Figure 54–5. Spinal infection: culosis with subligamentous spread.

tuber-A, Note the erosion of the anterior

surface (arrows) of multiple vertebral bodies B, In a different patient, a sagit-

tal T1-weighted spin echo MR image obtained after intravenous gadolinium administration shows involvement of multiple contiguous vertebral bodies (manifest as high signal intensity) and

anterior abscess formation (arrows),

with elevation of the anterior dinal ligament Intraosseous and poste-

longitu-rior abscesses are also seen (A, Courtesy

of A Nemcek, MD, Chicago, Ill B,

Courtesy of A D’Abreu, MD, Porto Alegre, Brazil.)

separation of abnormal and normal soft tissue Gas may

be identified in the infected soft tissue or, rarely, in theintervertebral disc itself

The MR imaging characteristics of infective tis are influenced by the specific nature and extent of theprocess and the precise imaging protocols used Further,the age of the patient affects these characteristics because

spondyli-of the changing constituency spondyli-of the bone marrow (i.e.,red versus yellow marrow) In acute pyogenic osteomye-litis, affected regions typically show decreased signal inten-

Figure 54–6. Spinal infection: residual deformity Klebsiella spondylitis developed in the cervical region in

this 41-year-old man A, Three weeks after the onset of infectious spondylitis, note the collapse and

fragmentation of the superior aspect of the fifth cervical vertebral body and lysis of the interior aspect of the

fourth cervical vertebral body (arrowheads) Soft tissue swelling is evident B, Two weeks later, angulation and

subluxation are apparent Soft tissue swelling is again seen.

Figure 54–7. Intervertebral disc infection: discitis This

6-year-old girl had symptoms and signs consistent with spinal infection.

Bacteriologic studies were not helpful Observe the narrowing

of the intervertebral disc between the second and third lumbar

vertebral bodies, with osseous radiolucency and sclerosis

(arrow-heads) The appearance is consistent with infection (Courtesy

of L Lurie, MD, Chula Vista, Calif.)

Figure 54–8. Spinal infection: role of CT scanning axial CT scan at the L4–L5 level documents the extent of spinal destruction and a soft tissue mass in paraspinal and intraspinal

Trans-locations (arrows) This mass explained the patient’s prominent

neurologic manifestations.

sity on T1-weighted spin echo MR images and increased

signal intensity on T2-weighted spin echo images (Fig

54–9) The conspicuity of the bone marrow infection on

these MR images depends on the extent of red and yellow

marrow in the vertebral body and is more variable on

T2-weighted spin echo MR images Imaging with long

repetition and echo times (as well as fat suppression) is

beneficial in demonstrating high signal intensity within

the marrow

With MR imaging, irregularity of the vertebral

end-plates and narrowing of the intervertebral disc may be

evident On T2-weighted spin echo MR sequences, the

infected disc reveals increased signal intensity with absence

of the normal nuclear cleft (i.e., the normal anatomic

structure that, on T2-weighted images, appears as an area

of signal void in the center of lumbar discs in subjects

30 years or older) The high signal intensity of the

inter-vertebral disc in cases of pyogenic spondylitis is an

impor-tant diagnostic sign Additional MR imaging findings of

pyogenic spondylitis are less frequent but include

epidural and paraspinal extension, posterior disc sion, vertebral collapse, and spinal deformity

protru-Infected marrow usually enhances diffusely after theadministration of gadolinium In some instances, how-ever, this technique may produce a decrease rather than

an increase in the contrast between normal and infectedvertebral bodies (Fig 54–10) The combination of con-trast enhancement and fat suppression in cases of pyo-genic spondylitis may eliminate this problem Vertebralmarrow involvement in cases of infection (or tumor) mayalso be effectively demonstrated by using short tau inver-sion recovery (STIR) sequences

Differential DiagnosisThe radiographic hallmark of infective spondylitis is inter-vertebral disc space narrowing, frequently accompanied

by lysis or sclerosis of adjacent vertebrae (Table 54–1)

A similar radiographic pattern can be encountered invarious articular disorders, such as rheumatoid arthritis,

charac-of the first and second lumbar vertebral bodies and the L1–L2 intervertebral

disc is evident on both images In (B),

note the increased signal intensity in the infected disc (Courtesy of D Belovich, MD, Mechanicsburg, Pa.)

Figure 54–10. Spinal infection:

MR imaging in pyogenic litis Infective spondylitis devel- oped in this 40-year-old man after multilevel cervical discography.

spondy-A, Routine radiography shows

narrowing of the intervertebral discs at the C4–C5 and C5–C6 levels Prevertebral soft tissue

swelling is also evident B, Sagittal

T1-weighted (TR/TE, 500/12) spin echo MR image reveals low signal intensity of the marrow of the fourth, fifth, and sixth cervical

vertebral bodies C, After

intra-venous administration of a linium contrast agent, sagittal T1-weighted (TR/TE, 500/12) spin echo MR image shows hyper- intensity in the prevertebral soft

gado-tissues (arrows) In comparison with the findings in (B), the marrow

involvement is less apparent.

infection Rarely, infections by gas-forming bacteria maylead to a vacuum phenomenon–like appearance.

In general, primary or metastatic tumor in the spinedoes not lead to significant loss of intervertebral discspace; the combination of widespread lysis or sclerosis of

a vertebral body and an intact adjacent intervertebral disc

is much more characteristic of tumor than of infection.Certain neoplasms such as plasma cell myeloma, chordoma,and even skeletal metastasis can extend across or aroundthe intervertebral disc to involve the neighboring vertebra,however Paraspinal masses occur in infective spondylitisand traumatic and neoplastic disorders Infection is likely

if such masses contain gas

Accurate radiographic differentiation of pyogenic tive spondylitis from granulomatous infections (tuber-culosis and fungal disorders) can be difficult Rapid loss

infec-of intervertebral disc height, extensive sclerosis, and theabsence of calcified paraspinal masses are findings thatare more typical of pyogenic infection

SACROILIAC JOINT INFECTIONSRoutes of Contamination

The sacroiliac joint may become infected by the togenous route, by contamination from a contiguoussuppurative focus, by direct implantation, or after surgery.Hematogenous involvement of this joint likely begins inthe subchondral bone of the ilium

hema-Contamination of the sacroiliac joint or neighboringbone can occur from an adjacent infection Pelvic abscessescan disrupt the anterior articular capsule or the perios-teum and cortex of the ilium or sacrum Thus, vaginal,uterine, ovarian, bladder, and intestinal processes can lead

to iliac or sacral osteomyelitis and sacroiliac joint ration by contiguous contamination (as well as by

suppu-the seronegative spondyloarthropathies, calcium

pyrophos-phate dihydrate crystal deposition disease, alkaptonuria,

and neuropathic osteoarthropathy; in each of these

dis-orders, however, clinical and additional radiographic

fea-tures usually ensure an accurate differential diagnosis

Sarcoidosis can occasionally be associated with disc

space narrowing and bone eburnation at one or more

levels of the spine Diminution of intervertebral disc

height and bony sclerosis are associated with

cartilagi-nous node formation (Schmorl’s nodes) In general, the

poor definition of the subchondral bone plate is less in

cases of cartilaginous nodes than in cases of infection

MR imaging can also be applied to the differentiation of

cartilage node formation and infection, although

diag-nostic difficulties are encountered The widespread

carti-laginous nodes detected in Scheuermann’s disease (juvenile

kyphosis) create an appearance that is not generally

con-fused with that of infection

Intervertebral (osteo)chondrosis also produces

inter-vertebral disc space narrowing and reactive sclerosis of

the neighboring bone (see Chapter 30) The resulting

radiographic picture can resemble that of infective

spondylitis In intervertebral (osteo)chondrosis, the

ver-tebral endplates are usually smooth and well defined,

although focal defects can represent sites of

interver-tebral disc displacement (cartilaginous nodes) Of

partic-ular diagnostic significance is the presence of one or

more radiolucent collections overlying the intervertebral

disc in intervertebral (osteo)chondrosis These vacuum

phenomena represent gaseous collections (nitrogen)

within the nucleus pulposus and are a reliable sign of disc

degeneration They are exceedingly rare in cases of disc

infection, and their detection makes the diagnosis of

infection very unlikely Similarly, the presence of gas in

the vertebral body virtually eliminates the diagnosis of

TABLE 54–1

Differential Diagnosis of Disorders Producing Disc Space Narrowing

Infection Poorly defined Variable* Rare † Absent Vertebral lysis, soft tissue mass Intervertebral Well defined Prominent Present Variable Cartilaginous nodes

osteochondrosis

Rheumatoid arthritis Poorly or well defined Variable Absent Absent or mild Apophyseal joint

Calcium pyrophosphate Poorly or well Prominent Variable Variable Fragmentation, subluxation dihydrate crystal defined

deposition disease

Neuropathic Well defined Prominent Variable Prominent Fragmentation, subluxation,

Sarcoidosis Poorly or well Variable, Absent Absent Soft tissue mass

prominent

*Usually evident in pyogenic infections and in tuberculosis in black patients.

† Vacuum phenomena may initially be evident when intervertebral osteochondrosis is also present or, rarely, when a gas-forming microorganism is responsible for the infection.

hematogenous spread via Batson’s plexus) Pressure sores

related to prolonged immobilization are not infrequent

in the sacral region and can lead to subsequent articular

and osseous infection Direct implantation of organisms

after diagnostic, therapeutic, or surgical procedures

represents another, though uncommon, source of

sacroiliac joint infection

Clinical Abnormalities

Pyogenic infection of the sacroiliac joint may develop in

patients of all ages Unilateral alterations predominate

Fever, local pain and tenderness, and a limp may be

evident Accurate diagnosis is often delayed in cases of

septic sacroiliitis, which increases the frequency of such

extra-articular contamination Elevation of the

erythro-cyte sedimentation rate and leukocytosis are common but

variable laboratory findings Identification of the

causa-tive organisms from blood culture or joint aspiration can

be difficult Gram-negative bacterial agents are especially

common in pyogenic arthritis of the sacroiliac joint in

intravenous drug abusers

Radiographic-Pathologic Correlation

In almost all cases of sacroiliac joint infection, a unilateral

distribution is encountered In pyogenic arthritis,

radiographic findings generally occur in 2 or 3 weeks and

are characterized by blurring and indistinctness of the

subchondral osseous line and narrowing or widening of

the interosseous space Although these two alterations

frequently coexist, their time of appearance is dictated by

the initial site of contamination: if osteomyelitis precedes

septic arthritis, bony abnormalities may antedate the

articular changes; if the joint is affected initially,

carti-laginous and osseous alterations may coexist In both

situa-tions, the most extensive findings are commonly evident

about the inferoanterior aspect of the joint (Fig 54–11)

Surrounding condensation of bone is variable in

fre-quency and degree, and it is influenced by the type and

virulence of the infecting microorganism

Other Diagnostic Techniques

Scintigraphy, with the use of technetium phosphate,

gallium, or both, may outline increased accumulation of

radionuclide when findings on routine radiographs and

conventional tomograms are unimpressive Abnormal

uni-lateral uptake of isotope in the sacroiliac joint indicates

infection until proved otherwise

CT scanning is valuable in the early diagnosis of septic

sacroiliitis, because it reveals cartilaginous and osseous

destruction as well as intraosseous gas, and as an aid to

aspiration and biopsy techniques The latter procedures

can be difficult without CT guidance (Fig 54–12)

MR imaging shows marrow edema in the sacrum and

ilium, irregularity of the subchondral bone on either side

of the joint space, joint fluid, muscle edema, fluid-filled

channels, sinus tracts, and fistulas Intravenous

adminis-tration of a gadolinium contrast agent can be used to

accentuate the MR imaging abnormalities and to

delin-eate adjacent soft tissue involvement (Fig 54–13)

Differential DiagnosisThe unilateral nature of infective sacroiliac joint disease

Figure 54–11. Sacroiliac joint infection: early abnormalities.

Pseudomonas osteomyelitis and septic arthritis developed in a

35-year-old male heroin addict Radiograph reveals changes in the right sacroiliac joint consisting of subchondral osseous erosion, poorly defined articular margins, and widening of the

joint space (arrows).

Figure 54–12. Sacroiliac joint infection: CT scanning In this 20-year-old intravenous drug abuser, CT scans with bone

(A) and soft tissue (B) windows show involvement of the left

sacroiliac joint (arrow) and an abscess (arrowheads) in the iliac

muscle (Courtesy of J Hodler, MD, Zurich, Switzerland.)

A

B

is its most useful diagnostic feature Bilateral symmetrical

or asymmetrical articular changes are characteristic of

ankylosing spondylitis, psoriasis, Reiter’s syndrome, osteitis

condensans ilii, and hyperparathyroidism Unilateral

changes can be encountered in rheumatoid arthritis,

gout, Reiter’s syndrome, psoriasis, and paralysis (because

of chondral atrophy)

INFECTION AT OTHER AXIAL SITES

In intravenous drug abusers, osteomyelitis and septic

arthritis of the sternoclavicular and acromioclavicular

joints, in addition to the spine and sacroiliac joint, may be

FURTHER READING

Allen EH, Cosgrove D, Millard FJC: The radiological changes

in infections of the spine and their diagnostic value Clin Radiol 29:31, 1978.

Batson OV: The vertebral vein system AJR Am J Roentgenol 78:195, 1957.

Brant-Zawadzki M, Burke VD, Jeffrey RB: CT in the tion of spine infection Spine 8:358, 1983.

evalua-Dagirmanjian A, Schils J, McHenry M, et al: MR imaging of vertebral osteomyelitis revisited AJR Am J Roentgenol 167:1539, 1996.

Fernandez-Ulloa M, Vasavada PJ, Hanslits ML, et al: Diagnosis

of vertebral osteomyelitis: Clinical radiological and graphic features Orthopedics 8:1141, 1985.

scinti-Goldin RH, Chow A, Edwards JE Jr, et al: Sternoarticular septic arthritis in heroin users N Engl J Med 289:616, 1973 Jamison RC, Heimlich EM, Miethke JC, et al: Non-specific spondylitis of infants and children Radiology 77:355, 1961 Larde D, Mathieu D, Frija J, et al: Vertebral osteomyelitis: Disk hypodensity on CT AJR Am J Roentgenol 139:963, 1982 Lewkonia RM, Kinsella TD: Pyogenic sacroiliitis: Diagnosis and significance J Rheumatol 8:153, 1981.

Modic MT, Weinstein MA, Pavlicek W, et al: Magnetic nance imaging of the cervical spine: Technical and clinical observations AJR Am J Roentgenol 141:1129, 1983.

reso-evident After urologic procedures or athletic endeavors,osteomyelitis of the symphysis pubis may be difficult todifferentiate from osteitis pubis Infection of the sternumand the manubriosternal and sternoclavicular joints canresult from direct hematogenous inoculation (Fig 54–14)

or secondary contamination resulting from local injury,surgery, or diagnostic or therapeutic procedures In somesites, such as the sternoclavicular joint, abscess formationand inflammation in nearby tissues are common, andthese complications are well studied by CT scanning or

MR imaging

Figure 54–13. Sacroiliac joint infection: MR imaging.

Staphylococcal infection of the left sacroiliac joint developed in

this 48-year-old woman A, The infectious process in the

sacrum and ilium is not well visualized on this transaxial

T1-weighted (TR/TE, 650/11) spin echo MR image because of the

similar signal intensity of the inflammatory response and the

hematopoietic bone marrow The soft tissue extension of

infec-tion is not evident either B, Transaxial fat-suppressed

T2-weighted (TR/TE, 6000/102) fast spin echo MR image reveals

high signal intensity in the sacrum and ilium, as well as in the

anterior and posterior soft tissues and musculature (arrows) C,

Transaxial T1-weighted (TR/TE, 500/11) spin echo MR image

obtained with fat saturation technique after the intravenous

injection of a gadolinium contrast agent reveals the

inflamma-tory reaction, with high signal intensity in the bone and about

the anterior and posterior abscesses Note the low signal

inten-sity of the fluid in the joint and in the soft tissues and

muscu-lature (Courtesy of M Schweitzer, MD, Philadelphia, Pa.)

Figure 54–14. Sternal infection Group B streptococcal ticemia resulting in infections in the hip, spine, and sternum developed in this 47-year-old man Transaxial CT scan shows a destroyed sternum and an anterior soft tissue mass, both con-

sep-taining gas (arrows), and mediastinal adenopathy Mediastinitis

was confirmed at surgery.

A

Murphy KJ, Brunberg JA, Quint DJ, et al: Spinal cord

infec-tion: Myelitis and abscess formation AJNR Am J

Neuro-radiol 19:341, 1998.

Numaguchi Y, Rigamonti D, Rothman MI, et al: Spinal epidural

abscess: Evaluation with gadolinium-enhanced MR imaging.

Radiographics 13:545, 1993.

Pinckney LE, Currarino G, Higgenboten CL: Osteomyelitis

of the cervical spine following dental extraction Radiology

135:335, 1980.

Rosenberg D, Baskies AM, Deckers PJ, et al: Pyogenic

sacroili-itis: An absolute indication for computerized tomographic

scanning Clin Orthop 184:128, 1984.

Sandrasegaran K, Saifuddin A, Coral A, et al: Magnetic nance imaging of septic sacroiliitis Skeletal Radiol 23:289, 1994.

reso-Sartoris DJ, Moskowitz PS, Kaufman RA, et al: Childhood diskitis: Computed tomographic findings Radiology 149:701, 1983.

Sharif HS: Role of MR imaging in the management

of spinal infections AJR Am J Roentgenol 158:1333, 1992.

Wiley AM, Trueta J: The vascular anatomy of the spine and its relationship to pyogenic vertebral osteomyelitis J Bone Joint Surg Br 41:796, 1959.