Ebook Basic musculoskeletal imaging: Part 2

(BQ) Part 2 book Basic musculoskeletal imaging presents the following contents: Orthopedic hardware and complications, signs in musculoskeletal radiology, shoulder MRI, knee MRI, spine MRI, musculoskeletal ultrasound, musculoskeletal scintigraphy,...

Orthopedic Hardware and

Complications

Reza Dehdari, MD Minal Tapadia, MD, JD, MA

INTRODUCTION

Interpretation of postoperative orthopedic radiographs

com-prises a significant portion of the practice of not only

subspe-cialized musculoskeletal radiologists but also general

radiologists A good foundation and understanding of the

most common performed orthopedic procedures is essential

for accurate interpretation of postoperative radiographs

This chapter reviews the basic concepts of joint replacement,

spinal fusion, and fracture fixation, which are some of the

most common procedures performed by orthopedic

sur-geons In addition, the postoperative evaluation of various

orthopedic hardware including the imaging findings for

common complications will be discussed

JOINT REPLACEMENT

Joint replacement is one of the most common orthopedic

procedures performed Generalized indications for joint

re-placement include severe osteoarthritis, avascular necrosis,

trauma, and inflammatory arthropathies such as rheumatoid

arthritis Absolute contraindications for joint replacement

include active local or systemic infection Relative cations include obesity, remote infection, unrepaired liga-mentous injuries, and neurologic impairment Prior to the advent of joint replacement, surgical management of a pain-ful or nonfunctional joint included joint arthrodesis (e.g., joint fusion), osteotomy, nerve division, and joint debride-ment Patients were afforded significant improvement in quality of life with the development of joint replacement techniques; however, older joint replacement components often suffered from premature wear Recent advances in bio-materials and joint replacement technology have led to marked improvements in the longevity of joint prostheses Orthopedic surgeons can now choose between a vast array of prosthetic devices, many based on preference and familiarity Though it is impossible for the radiologist to become familiar with all the different devices in the market, the structural ma-terial and complications are shared among the variety of dif-ferent prostheses

contraindi-The main components of any modern joint arthroplasty include a metal alloy and a plastic polyethylene liner The low coefficient of friction between the metal alloy component and the polyethylene component simulates movements of

10

Joint Prosthetic Complications Spinal Fusion

Spinal Instrumentation Surgical Approaches Postoperative Evaluation and Complications Fracture Fixation

Techniques in Fracture Fixation Conclusion

 CHAPTER 10

212

normal joints Alloys represent the metallic component of the

prostheses They are combinations of different metals such as

chromium–cobalt, chromium–cobalt–titanium, or

chromium–cobalt–molybdenum.1 These different alloys

have individual biomechanical properties based on their

metal composition, and differ in terms of their resistance to

stress, strain, and tension Polyethylene is the radiolucent

liner of the prostheses In other words, it is not seen on the

radiograph In order to secure the prosthesis, the prosthesis

may either be press fit into the bone or cemented to the bone

Polymethylmethacrylate is the most commonly used cement

to secure the prosthesis into the medullary cavity of the bone

Cement is seen as a radiopaque lining surrounding the

thesis Alternatively, porous-coated press-fit cementless

pros-theses demonstrate an irregular surface coated with lucent

bone growth-stimulating material to ensure adherence to the

surface.2 Another concept to be familiar with is the resistance

of a prosthetic implant to motion, whether in the

anteropos-terior (AP) direction or the axial direction A constrained

prosthesis has two components that are directly linked

to-gether As a result, there is full range of motion in only one

direction In a nonconstrained prosthesis, it is the muscles,

ligaments, and tendons that provide stability with no

connec-tion between the two prosthetic parts This not only provides

the greatest possible range of motion but is also most prone

to joint subluxation or dislocation Semiconstrained

prosthe-ses allow intermediate motion in a given direction.3

The postoperative radiograph evaluation includes at least

two radiographic views of the prosthesis at right angles to

one another (e.g., orthogonal views) in addition to any

spe-cific views particular for the joint imaged For example, a

complete examination of a total knee arthroplasty would

in-clude an AP view, a lateral view, and possibly a sunrise view

for adequate visualization of the patella The entire prosthesis

and surrounding bone need to be imaged on the

examina-tion The technical factors of the radiograph must allow the

examiner to distinguish between metal–bone, metal–cement,

and cement–bone interfaces Other radiologic examinations

such as arthrography, ultrasonography, computed

tomogra-phy (CT), magnetic resonance imaging, and nuclear

scintig-raphy also have specific roles in evaluating joint replacement

HIP PROSTHESES

Three types of hip prostheses exist: unipolar

hemiarthro-plasty, bipolar hemiarthrohemiarthro-plasty, and total hip arthroplasty

(Figures 10-1 and 10-2) A unipolar hemiarthroplasty involves

replacement of the femoral head and neck without alteration

to the native acetabulum The femoral component includes

either a noncemented or cemented femoral stem with a

femo-ral head that articulates directly with the native acetabulum

This is the least common hip prosthesis and is typically

per-formed in patients with femoral head or femoral neck

frac-tures and decreased life expectancy A bipolar hip arthroplasty

includes a femoral stem with a small diameter femoral head and a separate acetabular cup (Figure 10-1) The outer por-tion of the acetabular cap articulates with the native acetabu-lum, while the inner portion articulates with the femoral head

as one unit Again, the native acetabular surface is unaltered This design is most prone to dislocation as motion can occur between both the femoral head and acetabular component and external surface of the acetabular component and the na-tive acetabulum The total hip arthroplasty is the most com-mon type of performed hip arthroplasty (Figure 10-2) In a total hip arthroplasty, the articular surface of both the femur and the acetabulum is replaced These components may either

be cemented or noncemented The metallic acetabular cup includes a radiolucent polyethylene liner that articulates di-rectly with the metallic femoral head

The postoperative radiograph of the hip includes AP and lateral view including the entire femoral stem and acetabular component The AP film is used to measure the angle of in-clination that is optimal at 30–55° (Figure 10-2), and the lat-eral film is used to measure the angle of anteversion that is optimal around 15°.1,2 The femoral component should be

Figure 10-1 Bipolar prosthesis AP view of the

bipo-lar right hemiarthroplasty, with separate acetabubipo-lar cup Note the radiolucent native articular cartilage surface

Figure 10-2 Total hip replacement AP view of the

total hip arthroplasty, consisting of both the femoral and

acetabular components The polyethylene liner

separat-ing the acetabular cup from the femoral head is

radiolu-cent The AP view best illustrates the angle of inclination

(normal between 30 and 55°)

either parallel to the femoral shaft or in slight valgus Varus

alignment increases the risk of stem migration, which can

result in periprosthetic fractures (Figure 10-3) With varus

alignment, the lateral femoral cortex is most often injured

Regardless of the location of the periprosthetic fracture,

revi-sion to a longer-stemmed revirevi-sion prosthesis is often needed

The femoral component should also be symmetric in the

center of the acetabular component Smooth 2 mm or less

radiolucent lines at the bone–cement interface can be normal

if not progressive Subsidence (sinking in of the prosthesis) of

less than 2 mm is also within normal limits.4

KNEE PROSTHESES

Most knee replacements are total knee replacements involving

resurfacing of the femoral condyle and the tibial plateau (Figure

10-4) The patella may either be simply resurfaced, or a patellar

prosthesis (e.g., a button) may be attached (Figure 10-4C) The

B A

Figure 10-3 Loose stem total hip prosthesis (A) AP

radiograph shows significant femoral stem loosening (arrows) and varus alignment of the femoral stem tip

(B) Arthrogram of the hip reveals contrast accumulation

in between the bone and cement interface indicating loosening of the prosthesis stem (arrows)

Figure 10-4 Total knee arthroplasty (TKA) AP

(A), lateral (B), and sunrise (C) views of TKAs show

ce-mented tibial and uncece-mented femoral components In all images, the polyethylene component is radiolucent

and cannot be seen readily on radiograph (A) The

fem-orotibial component should be aligned in 4–7° of valgus, and the articular surface of the tibial component should

be aligned parallel to the ground TKAs may involve

simple patellar resurfacing (B) or placement of a lar button (C) Note in (C), patellar resurfacing and frac-

patel-ture of the patella are seen

patellar and tibial components may be cemented or cementless

The metallic femoral component articulates with a

metal-backed polyethylene tibial component, which is radiolucent

Tricompartmental knee prostheses can further be subdivided

into posterior cruciate ligament (PCL) sparing or sacrificing

prostheses PCL sparing prostheses are most commonly formed and have slightly improved gait To differentiate be-tween the two types of prostheses, a large box is seen in the femoral component on the lateral film that articulates with the polyethylene in the tibial tray that provides posterior stability.1,2

per-B A

Figure 10-5 Unicompartmental knee arthroplasty (UKA) AP (A) and lateral (B) radiographs of UKA The

radi-opaque line between the femoral and tibial components seen on the AP view (A) corresponds to a metallic marker within the polyethylene component Additionally, on the AP view (A), note the periprosthetic lucency (arrows) that

represents hardware loosening There is linear soft tissue calcification incidentally noted near the medial tibial condyle

Standing AP (Figure 10-4A), lateral (Figure 10-4B), and

patellar views (Figure 10-4C) are obtained when evaluating

the postoperative knee The optimal alignment for the

femo-rotibial component is 4–7° valgus in the AP projection (Figure

10-4A) and neutral to minimal flexion on the lateral

radio-graph (Figure 10-4B).2 In addition, the articular surface of the

tibial component of the prosthesis should be parallel to the

ground on the standing views (Figure 10-4A) The tibial

com-ponent should also cover the entire surface of the tibia to

pro-vide adequate support The femoral component should be 90°

to the long axis of the femoral shaft on the lateral view.1

Unicompartmental knee prostheses have been used in

younger patients with isolated medial or lateral

compart-ment arthritis (Figure 10-5) In these cases, a single femoral

condyle and its tibial articulating surfaces are resurfaced

Unicompartmental patellar prostheses have been shown to

result in suboptimal outcomes and are not routinely used

ANKLE PROSTHESES

The ankle is a complex joint, and success rate for joint placement has been suboptimal The lack of success is likely due to inability to duplicate the normal mechanics of the ankle joint and inability to restore the stabilizing effect of the ligaments Although second-generation ankle prostheses have had better outcomes than first-generation prostheses, ankle arthrodesis remains the treatment of choice in manag-ing the painful ankle joint

re-SHOULDER PROSTHESES

Three types of surgeries exist for shoulder replacement: hemiarthroplasty (Figure 10-6), total shoulder arthroplasty (Figure 10-7), and reverse shoulder arthroplasty (Figure 10-8)

A shoulder hemiarthroplasty is used in cases such as severe

 CHAPTER 10

216

Figure 10-6 Shoulder hemiarthroplasty AP

radio-graph shows shoulder hemiarthroplasty Note the

ab-sence of any glenoid components Also note that the

superior aspect of the prosthetic head lies above the

greater tuberosity; this positioning helps prevent

subacro-mial impingement

Figure 10-7 Total shoulder arthroplasty AP

radio-graph shows total shoulder arthroplasty Note the glenoid

component contains radiopaque and radiolucent parts

Also note minimal lucency surrounding the radiopaque

glenoid component suggestive of loosening

Figure 10-8 Reverse total shoulder arthroplasty AP

view shows reverse total shoulder arthroplasty Note the medialized center of rotation, which allows the deltoid muscle to substitute for the deficient rotator cuff muscu-lature to facilitate shoulder abduction

proximal humeral fractures and severe rotator cuff tear where the patient still possesses a normal glenoid The humeral component may be cemented or noncemented, and articu-late with the native glenoid A total shoulder arthroplasty, usually performed in severe glenohumeral osteoarthritis, has

a metal or polyethylene-backed glenoid component (Figure 10-7).3 The reverse shoulder arthroplasty is performed in pa-tients with a nonfunctioning rotator cuff due to massive rota-tor cuff tear (Figure 10-8) In this case, the ball-shaped glenoid component aligns with the cup of the humeral com-ponent The cup of the humeral component is connected to the stem portion of the prosthesis Because these designs are held in place by the surrounding rotator cuff, they are either semiconstrained or unconstrained and are more prone to dislocation.1

Postoperative views of the shoulder prosthesis include

AP view in internal and external rotation to evaluate for subsidence or upward migration of the humeral compo-nent In a patient with an intact rotator cuff, impingement

occurs if the most superior aspect of the prosthesis lies

below the level of the superior tip of the greater tuberosity

Trans-scapular Y or axillary views are also obtained to

as-sess for dislocation

ELBOW PROSTHESES

Total elbow prostheses consist of both the humeral and ulnar

components Elbow prostheses can be categorized by design,

either as linked or nonlinked Linked elbow prostheses can be

likened to constrained prostheses, whereas nonlinked elbow

prostheses can be likened to nonconstrained prostheses The

linked portions have a rigid hinge that connects the humeral

component to the ulnar component (Figure 10-9)

Loosen-ing, especially at the humeral component, is a major

prob-lem The unlinked prostheses have stemmed ulnar and

humeral components that articulate via an interposed

poly-ethylene liner In this case, stability is provided by the

adja-cent muscles, and intact tendons and ligaments Finally,

radial head prostheses may be performed in cases of

commi-nuted radial head fractures (Figure 10-10)

WRIST AND HAND PROSTHESES

Wrist arthroplasty is usually performed in patients with rheumatoid arthritis or severe osteoarthritis For replace-ment of individual carpal bones due to avascular necrosis or trauma, Silastic prostheses have been used The metacarpo-phalangeal and interphalangeal joints are commonly per-formed arthroplasties in patients with severe rheumatoid arthritis There are no clear indications in management, and

in most cases management often trends toward partial or total arthrodesis of the wrist and the hand

JOINT PROSTHETIC COMPLICATIONS

Bone fractures typically occur within the early postoperative period in patients with poor bone stock such as osteoporotic patients In the hip, excessive varus alignment of the femoral stem will eventually predispose to early periprosthetic frac-ture (Figure 10-3A), requiring a long-stem revision proce-dure Fractures of the prosthesis or cement are usually delayed complications secondary to long-term repetitive stress

B A

Figure 10-9 Constrained

left total elbow prosthesis

AP (A) and lateral (B)

radio-graphs of constrained left

total elbow prosthesis

Hinged prostheses often

suf-fer from loosening, as

exhib-ited by the periprosthetic

lucency surrounding the

hu-meral component that has

led to periprosthetic fracture

of the distal humeral shaft

(arrow)

 CHAPTER 10

218

Loosening is a common delayed complication shared by all

prostheses (Figures 10-3A,B, 10-5A, and 10-11) Repetitive

mechanical stresses can cause loosening at the cement–bone,

prosthesis–bone and cement–prosthesis interfaces Lucency

that is less than 2 mm in width and nonprogressive on

follow-up radiographs is considered normal Progression of lucency

greater than 2 mm or development of new, irregular areas of

lucency is likely secondary to loosening (Figures 10-3A,B,

10-5A, and 10-11).4 It is always important to have prior films

available in addition to short-term follow-up films to assess

progression of loosening In the hip, subsidence of the femoral

portion of the prosthesis that is greater than 5 mm is also

in-dicative of loosening Subsidence of the acetabular

compo-nent will also result in protrusio acetabuli, or migration of the

prosthesis into the pelvic cavity Other signs of loosening in

the hip prosthesis include cement fracture and sclerosis

(ped-estal formation) at the tip of the prosthesis.4

Infection is a serious delayed complication of any joint

replacement There is considerable overlap in differentiating

infection from loosening Additional clinical information,

Figure 10-10 Elbow radial head prosthesis AP view

of the right elbow illustrating radial head prosthesis

Figure 10-11 Loose femoral component of total

knee arthroplasty (TKA) Lateral view of the TKA

illus-trating loosening of the anterior aspect of femoral ponent at the site of the bone–metal interface (arrow), as evidenced by the lucency between the femoral cortex and prosthesis

com-including laboratory analysis, is needed to assess the hood of infection Radiographically, the presence of irregular periprosthetic lucency, periosteal reaction, and bone destruc-tion is suggestive of infection rather than loosening (Figure 10-12A,B) Focal areas of lucency are more suggestive of loos-ening than the generalized lucency seen in infection Addi-tional signs of infection include soft tissue swelling, large joint effusion (Figure 10-12B), and abscess formation Joint aspiration is the most definitive technique to diagnose septic arthritis Arthrography can also be used to diagnose both loosening and infection Initially, the joint is aspirated for laboratory analysis Next, iodinated contrast is injected into the joint Contrast accumulation around in the region of periprosthetic lucency is suggestive of loosening (Figure 10-3B)

likeli-or infection Antibiotic-laced cement may be used after moval of infected prosthesis (Figure 10-13) Other methods

re-B A

Figure 10-12 Infected total knee arthroplasty (TKA) AP (A) and lateral (B) views of the TKAs (A) Both the

femo-ral and tibial components of the TKA exhibit irregular periprosthetic lucency (arrows), suggestive of infection (B) The

lateral view readily reveals a large posterior effusion (arrow) and bony destruction that are hallmarks of infected joint prostheses

to diagnose prosthetic infection include ultrasound-guided

joint fluid aspiration and nuclear scintigraphy.5

Another relatively common complication of joint

replace-ment is particle disease that is a host inflammatory osteolytic

response, which occurs after shedding of portions of the

pros-thesis (Figure 10-14) It is usually a response to the

radiolu-cent polyethylene liner or methylmethacrylate Although they

occur more commonly in hip prostheses, particle disease can

also occur in any other prostheses Particle disease usually

manifests as multiple well-defined lucencies that do not

con-form to the shape of the prosthesis (Figure 10-14) Additional

foci of endosteal scalloping may also be seen Unlike infection,

a periosteal reaction is not seen in cases of particle disease

Along the same lines, polyethylene wear is a common entity

seen in both the hip and knee prosthesis (Figure 10-15)

Dislocation or subluxation may occur in either the early

or late postoperative period This is a greater problem in semiconstrained or nonconstrained arthroplasties such as the shoulder or the elbow if the surrounding muscles, ten-dons, and ligaments do not have the adequate strength to prevent subluxation and dislocation Another complication seen in various joint replacements is heterotopic ossification seen around the periprosthetic region Heterotopic ossifica-tion can also be seen with other types of hardware as well (Figure 10-16) Patients at higher risk of heterotopic ossifica-tion include patients with a history of ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis (DISH), and hyper-trophic osteoarthritis.1 In advanced cases, heterotopic ossifi-cation can limit mobility of the joint and may eventually cause joint fusion

 CHAPTER 10

220

Figure 10-13 Infected total knee arthroplasty

(TKA) with antibiotic cement spacer AP view of the

in-fected TKA with antibiotic cement spacer Inin-fected TKAs

are often revised in a staged fashion: first, the infected

TKA is removed and an antibiotic spacer is placed as

illus-trated, and subsequently once the infection has been

eradicated with irrigation, debridement and antibiotics,

the revision surgery takes place

Figure 10-14 Aggressive granulomatosis (particle

disease) in total hip arthroplasty (THA) AP view of the

left hip arthroplasty with particle disease, as evidenced

by lucencies around the prosthesis components and multiple metallic particles in the joint space

SPINAL FUSION

Spinal fixation procedures are commonly encountered in

to-day’s radiologic practice The most common indication for

spinal surgery today is degenerative disk disease There are

various other indications for spinal surgery including trauma,

tumors, infection, scoliosis, and spondylolisthesis The goal

of spinal fixation devices is to restore anatomic alignment;

stabilize the bone during fusion; and replace bone defects in

cases of trauma, tumor, or infection The same principles that

apply to other joints also apply to the spine Fusion of a

dis-eased joint will eliminate pain by eliminating the motion

be-tween the painful joint, such as severely diseased disks within

the lumbar spine.6 It usually takes 6–9 months for solid fusion

to be seen radiographically The other important concept to

realize is that the spinal hardware is used to provide

temporary fixation and stability by immobilizing the bone The function of the hardware is complete when osseous fusion occurs Most intact implants are generally left in place after bony fusion due to the morbidity involved in recurrent spinal surgery This section will discuss the procedures and range of hardware devices used in spinal fixation The post-operative complications will then be discussed

SPINAL INSTRUMENTATION

Although many spinal fusion instrumentation systems exist, the basic components of each system can be classified into a few general categories Interpedicular screws are connected either by rods or plates that span single or multiple vertebral body segments (Figures 10-17 to 10-22) Plates are also com-monly used in conjunction with cortical screws in anterior fusion of the cervical spine (Figure 10-17A,B) There are var-ious sizes of plates that can be used for both the anterior and

Figure 10-15 Polyethylene liner wear and

dis-placement AP view of the right hip The femoral head of

the prosthesis is not centered in the acetabular cup due

to wear and displacement of the polyethylene liner

exten-posterior fusion procedures Rods are used to provide

stabil-ity over short or long segments (Figures 10-17 to 10-22) A

common example is the Harrington rod used for scoliosis of

the spine Harrington rods help provide distraction along the

concavity and compression forces across the convexity in the

treatment of scoliosis In addition, they may be bent

intraop-eratively to accommodate kyphosis and lordosis Rods can be

attached to the spine by pedicle screws, wires, or cables Disk

spacers are inserted into the intervertebral disk space after the

diseased disk is removed (Figures 10-17A,B and 10-19A,B)

They are made of titanium or radiolucent material such as

polyether ether ketone (PEEK) Surrounding bone graft

ma-terial is also used surrounding the disk spacer to provide

ad-ditional stability Bone graft material is also used within the

posterior elements in posterior spinal fusion to provide

additional stability Finally, corpectomy (vertebral body

replacement) may be necessary after major trauma or

destruction of the vertebral body by tumor or infection

Usually, the vertebral body is replaced by an expandable low cylinder packed with bone graft material or cement.6,7

hol-SURGICAL APPROACHES

Surgical approaches to the spine can be generally divided into the anterior and posterior approaches In the lumbar spine, posterior interbody fusion has a lower morbidity and faster recovery rate than an anterior fusion Posterior lumbar spinal fusion is commonly used in the treatment of degenerative disk disease, infection, and spondylolisthesis Bilateral lami-nectomies are first performed for spinal decompression Bone grafts are placed within the posterior elements to facili-tate osseous fusion Discectomy is then performed with in-tervertebral body disk spacers and surrounding bone graft placement Finally, interpedicular screws with vertical plates

 CHAPTER 10

222

B A

Figure 10-17 Anterior cervical fusion AP (A) and lateral (B) radiographs of cervical fusion instrumentation show

anterior cervical fusion of C4-5 and C5-7 via plates and vertebral body screws The radiopaque vertical lines between the fused vertebral bodies represent the borders of each intervertebral disk spacer These lines represent embedded metallic markers in each intervertebral spacer that aid in detecting migration of spacers on follow-up examinations

B A

Figure 10-18 Posterior cervical fusion AP (A) and lateral (B) radiographs of the cervical fusion instrumentation

show posterior cervical fusion of C2-T1 with pedicle screws and rods On the lateral view (B), intervertebral bone graft

has incorporated, resulting in stable fusion of adjacent vertebral bodies

B A

Figure 10-19 Lumbar spinal fusion with vertebral screws and rods, and intradiscal bone graft AP (A) and

lat-eral (B) views of the lumbar spine, demonstrating posterior interbody fusion of L4-L5 with intervertebral disk spacer

bone graft

or rods are placed to reinforce stabilization (Figures 10-19 to

10-22) Another modified type of posterior approach is the

transforaminal fusion that leaves the midline posterior

struc-tures intact In this case, a partial facetectomy is performed to

gain access to the disk space for discectomy, bone graft

place-ment, and subsequent vertebral body fusion.7

Alternatively, an anterior fusion can be performed, which

allows for better access to the disk space when performing

discectomy and vertebral body fusion In the cervical spine,

the anterior approach to fusion (Figure 10-17A,B) is usually

performed for patients with painful herniated disks It is the

preferred method due to the risk of cord manipulation from

a posterior approach, as well as the risk to vital structures

such as the trachea, the esophagus, the lungs, and the carotid

artery.8 First, the herniated portion of the disk or the entire

disk is removed Next, bone graft is placed to facilitate

inter-vertebral body fusion, with anterior plate and screws fixation

for further stability Finally, spinal corpectomy is performed

in patients with history of spinal fracture, tumor, infection or

severe degenerative disk disease, all of which may result in compression of the central canal and/or nerve roots An ante-rior or anterolateral approach is used The disease or dam-aged vertebral bone is first removed The superior and inferior disks are also removed, and bone graft is placed in place of the removed vertebral body, which results in fusion

of the adjacent vertebral bodies Side plates and screws are used to reinforce the fusion

POSTOPERATIVE EVALUATION AND COMPLICATIONS

AP and lateral radiographs of the spine are necessary for postoperative evaluation In certain cases, oblique images may be ordered as well Additional flexion and extension views aid with assessment of spinal stability When radio-graphs are nondiagnostic, CT with multiplanar reconstruc-tions provides better assessment of the hardware and evaluation of loosening, infection, and pseudoarthrosis

 CHAPTER 10

224

Early postoperative complications include postoperative

hematoma, infection, and meningocele formation In

evalu-ating transpedicular screws, it is important that they do not

breach the pedicle and cause damage to the nerve roots that

course along the pedicle.9 In addition, the tip of the vertebral

body screw must not breach the anterior cortex

Alterna-tively, anteriorly placed screws may penetrate the posterior

cortex and cause impingement on the cord Intervertebral

spacers and bone grafts can also herniate anteriorly or

poste-riorly and cause neurologic compromise

In terms of spinal surgical hardware, complications

in-clude fracture, migration, and dislodgment of the implant

Fractures of hardware components include broken screws

(Figure 10-20), broken wires, and fractures of the rods

Hardware fracture is usually a result of metal fatigue due to

continued stress from flexion and extension This causes

motion and instability of the fusion with subsequent

forma-tion of a pseudoarthrosis, which represents fibrous rather

than osseous union of the fusion.6,8 This will in turn increase

the likelihood of loosening and hardware fracture Hardware instability and motion will also cause bony resorption and loosening around the screws and other implants (Figure 10-21) An important risk factor for loosening is osteoporo-sis, as it is difficult for the screw to obtain purchase in an osteoporotic vertebral body

Infection is an uncommon complication that usually presents with irregular progressive lucency and destruction surrounding the implant An associated discitis/osteomyelitis may be present with destruction and collapse of the infected disk space MRI, nuclear medicine scintigraphy with WBC scan, and possibly CT-guided aspiration may be needed for further characterization of the infection.6 One other compli-cation of spinal fusion must be noted: although fusion may

be successful, it will eventually cause increased stress at levels above and below the level of surgical fixation Facet arthritis and degenerative disk and facet disease are common above and below the level of the fusion (Figure 10-22).8 Furthermore,

Figure 10-20 Broken pedicular screws Lateral

radio-graph of the lumbar spine shows L4-S1 posterior fusion

via rods and pedicle screws, exhibiting breakage of the

L4 and L5 pedicle screws within the pedicle

Figure 10-21 Loose pedicular screws Lateral

radio-graph of the lumbar spine shows L3-S1 posterior fusion with rods and pedicle screws, exhibiting lucency sur-rounding the L4 and L5 screw threads (arrows) sugges-tive of loosening

Figure 10-22 Lumbar fusion with adjacent

degen-erative disc stress and disease Lateral radiograph of the

lumbar spine shows L3-S1 posterior fusion via rods and

pedicle screws, with large anterior marginal osteophyte

seen at L2-L3 (arrow) with marked endplate subchondral

sclerosis indicative of vertebral body degenerative

changes and discogenic sclerosis as a result of abnormal

stress at the site of the fused and unfused segments

fused bones are less mobile, making the adjacent vertebral

bodies more prone to fracture in cases of trauma

FRACTURE FIXATION

In this section, the nonoperative and operative methods of

fracture fixation including the instrumentation, approaches,

and complications will be discussed The goal of fracture

fixation is to stabilize the fractured bone in anatomic

align-ment in order to promote quick healing and optimal

func-tional recovery To understand fracture fixation, two concepts

of bone healing must first be understood: callus healing and

callus-free bone healing Bone healing via callus formation is

also referred to as indirect fracture healing It occurs in

un-stable or relatively un-stable mechanical conditions such as bone

immobilized by a cast or a splint, or via intramedullary nail

fixation or bridging plates that simply span the fracture site without screw fixation directly adjacent to the fracture site The healing process with callus formation can be divided into four stages Initially, there is formation of hematoma and a host inflammatory response surrounding the fracture site Next, soft callus develops at 2–3 weeks followed by hard cal-lus formation at 2–4 months Radiographically, solid callus is seen at this time bridging the fracture site Finally, in the next months to years, new bone will undergo continuous remod-eling with bone resorption and apposition until complete remodeling occurs with restoration of the normal longitudi-nal axis of cortical bone at the fracture site

However, when a fracture is surgically reduced by plates and screws, fractures heal without callus formation This type

of fracture healing is often referred to as “direct” fracture healing In this case, there is a very small gap between the fracture fragments, and fracture healing is initiated by the Haversian system of remodeling The Haversian system is the functional unit of cortical bone Cortical bone is made out of multiple layers of lamellar bone with a layer of osteoclasts at the tip The osteoclasts function to resorb the end of the frac-ture, while osteoblasts form new bone behind the osteoclasts, thus creating numerous microscopic bony bridges across the fracture site Healing without callus formation is the underly-ing mechanism for internal fixation and is advantageous due

to the significantly decreased healing time.1

TECHNIQUES IN FRACTURE FIXATION

The first decision by the orthopedic surgeon is whether open

or closed reduction of the fracture is necessary If the fracture

is minimally displaced or if the degree of displacement will not affect a patient’s final functional status, conservative treatment is performed The surgeon may first perform closed manipulative reduction In this method, the fracture fragments are manipulated through the soft tissues and re-stored to as near as normal anatomical position as possible External immobilization devices can then be used for tempo-rary immobilization or for definitive treatment External im-mobilization comes in the form of external slings, splints, or casts After immobilization, whether following operative or nonoperative reduction, close watch must be kept for swell-ing in a close fitting cast or splint as it may cause impairment

to the circulation and vascular comprise to the distal part of that limb, possibly resulting in a compartment syndrome Conversely, fractures of certain anatomical sites such as ribs, scapula, and clavicle need not be immobilized as they will heal well without immobilization.10

In certain fractures, such as fractures of the femoral shaft

or distal humeral shaft, the elastic pull of the muscles tends to cause overlap of the fracture fragments In such cases, it is difficult to maintain anatomic position by the use of a splint

or a cast As a result, surgical pinning or wiring is performed, such as pinning the distal femur with attachment to a traction

 CHAPTER 10

226

device in order to counteract the weight of the pull of the

muscles and subsequent sustained traction on the distal

frac-ture fragment In the distal femur, complications of traction

pinning include damage to the quadriceps and surrounding

neurovascular structures

Internal fixation is the method of choice when acceptable

alignment is not possible by splinting alone Internal fixation

helps restore anatomic alignment with subsequent full

func-tion of the limb and rapid immobilizafunc-tion of the patient The

devices used for external fixation fall under several

catego-ries, which will be discussed in turn

Screws are the most common orthopedic devices used in

fracture fixation Two generalized categories exist Cortical

screws are fully threaded and tend to have finer threads They

are designed to anchor into cortical bone Cancellous screws,

however, are usually partially threaded, and have coarser

threads that help anchor into soft medullary bone

Compli-cations of screws include loosening, fracture, and migration

(Figures 10-23 to 10-27) Progressive lucency around a screw

on follow-up radiographs is indicative of loosening

Figure 10-23 Broken screw AP view of the right

foot, illustrating breakage of Lisfranc joint screw

Figure 10-24 Multiple fractures of interlocking

screws AP view of the knee demonstrating breakage

of distal interlocking screws of cephalomedullary nail, resulting in distal migration of the nail

Figure 10-25 Breakage of syndesmotic screws

Mortise view of the right ankle depicting breakage of syndesmotic screws

Figure 10-26 Migration of dynamic hip screw AP

view of the left hip demonstrating superolateral

migra-tion of dynamic hip screw Note telescoping and posterior

retraction of the dynamic hip screw

Figure 10-27 Superior migration of cannulated

screw AP view of the left hip demonstrating the superior

cannulated screw appears to have entered the hip joint, which puts the patient at risk of acetabular damage and subsequent osteoarthritis

Plates are usually made out of titanium or stainless steel

and are applicable to fixation of long bone fractures (Figures

10-28 and 10-29) Six to eight screws are usually fixed to a

plate by threaded holes It is important to note that there is

mobility between the fracture fragments when under a stress

load This is eliminated with usage of a special type of screw,

the interfragmentary screw The interfragmentary screw is a

screw that crosses the fracture line (Figure 10-29), ideally

perpendicular to the fracture line In crossing the fracture

line, the screw is able to compress the fracture fragments

to-gether This helps abolish motion at the fracture site and

promotes faster healing without callus formation In

suc-cessful internal fixation, there is gradual loss of the lucency

at the fracture interface Any gap widening or fracture of the

plate is a symptom of instability (Figures 10-30 and 10-31)

Another important class of fractures are fractures that involve

the articular surface Intra-articular fractures require very

precise anatomic reduction in near-perfect anatomic

align-ment to avoid developalign-ment of callus formation, as this will

increase the chance of developing early post-traumatic osteoarthritis.1,10

Complex pelvic and acetabular fractures require the use

of reconstruction plates for fixation These plates are very malleable and can be shaped to stabilize complex fractures involved in the pelvis Another well-known plate and screw apparatus is the dynamic hip screw used to treat intertro-chanteric fractures (Figure 10-26) Initially a side plate is af-fixed to the distal femur and attached with multiple cortical screws The side plate consists of a hollow barrel proximally,

in which a screw is inserted transfixing the femoral head and neck The plate has a hole toward the proximal end, in which

a screw may be inserted that ends in the femoral head The dynamic hip screw side plate and screw, like any other hard-ware, are subject to fracture migration and loosening (Figure 10-26) Given the large surface area contact of such side plates with the cortex, cortical blood supply may be compro-mised, which may result in nonunion or delayed union

 CHAPTER 10

228

B A

Figure 10-29 Plate and screw fixation of olecranon

fracture Plate and screw fixation of olecranon fracture

with axially oriented interfragmentary screw traversing

fracture site

Figure 10-28 Ankle

frac-ture with plate and screw fixations AP (A) and lateral

(B) views of the right ankle

joint, exhibiting bridge plate fixation of oblique fibular fracture with malleolar screw fixation of medial malleolus fracture

Intramedullary nails are used in the treatment of long bone

fractures usually in the middiaphyseal region (Figures 10-32 and 10-33) Intramedullary nails are commonly used in tibial and femoral fractures (specifically, intertrochanteric fractures) These surgeries are usually performed with minimal tissue ex-posure and may be performed in retrograde or anterograde fashion Tibial intramedullary nails have transverse holes at both ends that allow perpendicular interlocking screws to be placed leading to increased stability of fixation and prevention

of intramedullary nail rotation Femoral intramedullary nails typically have distal interlocking screws, as well as a transverse hole at the proximal end in which a cephalomedullary screw may be inserted that ends in the femoral head Potential com-plications of intramedullary nail placement are violation of the joint space and damage to the internal cortical blood sup-ply that can subsequently increase the rate of infection For

fixation of femoral neck fractures, cannulated screws are often

used (Figure 10-27) These screws have a hollow core, which allows them to be inserted percutaneously over a guide wire, with less risk to the blood supply of the femoral head Three screws are typically used to achieve fixation, with two screws placed inferiorly and one placed superiorly.11,12

Wires are commonly used as an alternative to screws

for fixation of small osseous fracture fragments Multiple

Figure 10-30 Fracture of the femoral contoured

plate Fracture of contoured lateral femoral plate with

as-sociated subtrochanteric fracture through fracture callus

with associated varus malalignment and nonunion

Figure 10-31 Fracture of cerclage wires and

mis-placement of screw at fracture site Fracture nonunion

leading to instability and subsequent hardware failure

There is screw breakage and rupture of proximal cerclage

wires with resultant plate separation from cortical bone

Note one of the screws was erroneously placed in the

fracture site

thin-diameter Kirschner wires (also known as K-wires) are sometimes used in stabilizing comminuted intra-articular dis-tal radial fractures (Figure 10-34) as well as many types of pha-langeal and metacarpal fractures Cerclage wires are another common type of wire used in encircling and fixation of frac-ture fragments They are commonly used for reinforcement in revision arthroplasties due to periprosthetic fractures in order

to provide additional support Finally, tension band placement

is commonly used in the fixation of olecranon and patellar fractures In this method, cerclage wires are used to fixate the two fracture fragments and are stabilized by additional Kirsch-ner wires or screws When placed correctly, the wires convert the tensile forces of the muscle on the fracture fragments into

a compressive force that promote fracture healing.10–12

The indications for external fixation include open tures, periarticular fractures, and pediatric factures in which the growth plate is to be avoided In open fractures, there is usually significant surrounding soft tissue injury, possible vas-cular compromise, and increased risk of infection As a result,

Figure 10-32 Intramedullary rod and locking

screws Tibial intramedullary nail with one proximal and

one distal interlocking screw, transfixing a proximal verse tibial fracture Note the formation of early bridging callus

trans- CHAPTER 10

230

Figure 10-33 Femoral cephalomedullary nail

Ceph-alomedullary femoral nail with distal interlocking screws

Figure 10-34 External fixator and K-wire fixation of

distal radial fracture AP view of the right wrist,

demon-strating K-wire fixation of distal radius fracture with ning external fixator in place

span-internal fixation is undesirable due to both increased damage

to surrounding soft tissues and increased risk of infection

with the use of internal plates and screws External fixators are

made of a combination of pins and rods that are placed

per-cutaneously into the bone above and below the fracture site

(Figure 10-34) These systems allow the easily adjustable

com-pression of the bone fragments A well-known type of

exter-nal fixator is the Ilizarov frame that uses thin wires to secure

the proximal and distal fracture fragments, with the wires

then attached to an outside ring frame that are all lined and

connected by adjustable rods.10 The Ilizarov device is used in

the treatment of limb lengthening procedures as well as

com-plex bone fractures In external fixation, daily cleansing must

be performed in order to keep the pin sites clean as infection

could cause the pin sites to loosen and require their removal

CONCLUSION

Various types of fracture hardware and fixation methods

have been discussed The type of fracture, anatomical site age,

and comorbidities of the patient will dictate what approach

the surgeon will have in treatment of the fracture As with

joint replacement, and spinal fixation, many similar cations apply including infection, loosening, and hardware fracture It is important for the radiologist to have familiarity with the most common orthopedic procedures in order to better recognize complications involved with various proce-dures As with other regions of the body, prior imaging and follow-up imaging, in addition with the clinical information

compli-is essential in helping to provide the correct diagnoscompli-is

PEARLS

The main components of most joint prostheses include

a metal alloy and a polyethylene liner The low cient of friction between the two components simu-lates the movement in healthy joints

coeffi-The cement–prosthesis, bone–cement, and prosthesis–bone interfaces are evaluated in joint prostheses to assess for loosening Progression of lucency greater than 2 mm or development of new, irregular areas of lucency is likely secondary to loosening

 Differentiating loosening from infection may be difficult

due to considerable overlap between the two entities

Joint aspiration, arthrography, and nuclear scintigraphy,

combined with additional clinical information, are

needed to assess for the likelihood of infection

 In the spine, fusion of a diseased joint will eliminate

pain by eliminating the motion between the painful

joint The function of spinal hardware is used to

pro-vide temporary fixation and stability by immobilizing

the bone in preparation for permanent osseous fusion

 In spinal hardware fixation, hardware fracture is

usu-ally a result of metal fatigue due to continued

me-chanical stress from flexion and extension causing

instability of the fusion with subsequent

pseudoarthro-sis Pseudoarthrosis itself can be a cause of pain

 Fracture healing can be divided into callus healing and

callus-free healing Internal fixation is based on the

principle of Haversian remodeling of healing without

callus formation and is advantageous due to

signifi-cantly decreased healing times

 Nondisplaced or minimally displaced fractures that do not

have an effect on patient functional status are usually

treated with closed manipulative reduction and casting

 Open fractures or fracture with extensive soft tissue

involvement may be treated with external fixation as

there is greater damage to the surrounding soft tissues

and increased risk of infection with internal fixation

 Intra-articular fractures require very precise anatomic

reduction as any callus formation at the articular

sur-face will expedite the development of post-traumatic

osteoarthritis

REFERENCES

1 Bonakdarpour A, ed Diagnostic Imaging of Musculoskeletal

Ra-diology: A Systematic Approach New York, NY: Springer;

2009:203-239, 497-525

2 Rabin D, Calire S, Kubicka R, et al Problem prostheses: the

ra-diologic evaluation of total joint replacement Radiographics

1987;7:1107-1127

3 Taljanovic MS, Jones MD, Hunter TB, et al Joint arthroplasties

and prostheses Radiographics 2003;23(5):1295-1314.

4 Ostlere S, Soin S Imaging of prosthetic joints Br Inst Radiol

2003;15:270-285

5 Tehranzadeh J, Schneider R, Freiberger RH Radiological

evalua-tion of painful total hip replacement Radiology

1987;141(2):355-362

6 Hayeri M, Tehranzadeh J Diagnostic imaging of spinal fusion

and complications Appl Radiol 2009;38:14-28.

7 Rutherford E, Tarplett L, Evan D, Harley J, King L Lumbar spinal

fusion: hardware, techniques and imaging appearances

Radio-graphics 2007;27:1737-1749.

8 Young P, Berquist T, Bancroft L, Peterson J Complications of

spinal instrumentation Radiographics 2007;27:776-789.

9 Tehranzadeh J, Ton JD, Rosen CD Advances in spinal fusion

Semin Ultrasound CT MR 2005;26:103-113.

10 Principles of Fracture Management vealed.com/files/11224-53.pdf

www.medicaltextbooksre-11 Taljanovic MS, Jones MD, Ruth JT, Benjamin JB, Sheppard JE,

Hunter TB Fracture fixation Radiographics

2003;23(6):1569-1590

12 Lakatos R, Keenan M General Principles of Fracture Fixation http://emedicine.medscape.com/article/1269987-overview# aw2aab6b3

This page intentionally left blank

Rim Sign Rugger Jersey Spine Sausage Digit Sail Sign Scotty Dog Sign Swan Neck Deformity Teardrop Sign (Orbits) Teardrop Sign (Ankle) Terry-Thomas Sign Tooth Sign Trolley-Track Sign Trough Line Tumbling Bullet Sign Vacuum Phenomenon

Blade of Grass Sign

Blister of Bone Sign

Bone Bruise Sign

Cortical Ring Sign (Signet Ring Sign)

Cotton Wool Sign

Crescent Sign

Crowded Carpal Sign

Cupid’s Bow Sign

Dagger Sign

Deep Lateral Femoral Notch Sign (Deep Sulcus Sign)

Double PCL Sign

Drooping Shoulder Sign

Drunken Waiter Sign

Elbow Fat Pad Sign

Fallen Fragment Sign

FBI Sign

Fish Vertebra

Fluid-Fluid Level

 CHAPTER 11

234

INTRODUCTION

A sign is a mark carrying a conventional meaning and used

in place of words to convey a complex notion In medicine, a

sign is an objective evidence of disease specially observed

and interpreted by a physician Multiple signs are described

in the radiology literature The recognition of these signs

allows the radiologist and the clinician to make a specific

diagnosis or give a brief differential diagnosis We have

com-piled a collage of easily recognizable signs in musculoskeletal

radiology Familiarity with these signs can direct the

radiol-ogist toward an accurate diagnosis, timely intervention, and

astute management These signs are illustrated with

radio-graphs to help elucidate direct or indirect evidence of the

pathology and mechanism of injury Findings are best

appreciated on different imaging modalities; for example, an

axial computed tomography (CT) image of the spine will

confirm spondylolisthesis suspected on a radiograph

The adage, a picture is worth a thousand words, is true in

this context However, pattern recognition requires practice

Familiarization with these signs helps build a mental archive

for image recall

ABSENT BOW TIE SIGN1

Introduction and Anatomical Context: Normal menisci can

be seen as a series of hypointense classic bow ties on sagittal

magnetic resonance imaging (MRI) The knee joint is

cush-ioned by fibrocartilaginous medial and lateral menisci The menisci lie along the margin of proximal tibial articular sur-face Menisci act as shock absorbers and allow smooth move-ment of joint surfaces over each other

Etiology: Post-traumatic Medial meniscus is more

com-monly injured than lateral meniscus Most common cause of lateral meniscus injury is a discoid meniscus (Figure 11-1)

Radiological Findings: The second image reveals loss of the

normal bow tie appearance of the meniscus The “absent bow tie” is a good sign of a bucket handle tear of the meniscus The absence of the normal bow tie is secondary to the dis-placed fragment that makes up the “handle” of the bucket The absent bow tie sign mandates that at least two adjacent sagittal images with a normal meniscal body segment appear-ance are not present A word of caution is dependent on the cuts; sometimes one of the two bow ties may be absent with-out a real bucket handle tear Therefore, correlation with the coronal and axial images can be helpful

Diagnosis: Bucket handle tear of menisci.

Imaging Modality: MRI.

PEARLS

Absent bow tie sign is present when two adjacent sagittal MRIs exhibit a discontinuous body of the meniscus

Figure 11-1 Absent bow tie Two consecutive sagittal cuts of proton density MRIs of the peripheral medial meniscus

of the knee

ANTEATER NOSE2

Introduction and Anatomical Context: Anteater nose is a

direct sign of calcaneonavicular coalition Most common

clinical presentation is with anterolateral foot pain due to

degenerative osteoarthritis and pes planus

Etiology: Congenital (most common cause) (Figure 11-2).

Radiological Findings: Elongated tubular extension on

lat-eral radiograph This image has been likened to the elongated

nose of the anteater The findings are confirmed on axial CT

scan that shows a bone bridge between the calcaneus and the navicular

Diagnosis: Calcaneonavicular coalition.

Imaging Modality: Radiograph.

PEARLS

Direct sign of calcaneonavicular coalition

Confirmed on axial CT images

C

D

Figure 11-2 Anteater nose (A) Lateral radiograph of

the foot shows anteater nose (arrow) (B) Anteater drawing

(Used with permission from Arash Tehranzadeh, MD)

(C) Oblique radiograph of the foot shows fibrous coalition

of calcaneal navicular bones (arrow) (D) CT images of the

ankle show fibrous coalition of the calcaneal navicular bones (arrows)

 CHAPTER 11

236

Radiological Findings: Sagittal T2-weighted MRI of the

knee with anteriorly displaced/subluxed tibia, relative to femur Abnormal signal intensity seen in the ACL is sugges-tive of a tear This sign is the MR equivalent of the clinically elicited anterior drawer sign indicating ACL teat

Diagnosis: ACL injury.

Imaging Modality: MRI.

PEARLS

Anterior drawer sign is an indirect evidence of ACL injury Diagnosis is confirmed by documenting intralig-amentous edema, hemorrhage, ligament discontinu-ity, or contour irregularity

BAMBOO SPINE4

Introduction and Anatomical Context: Ankylosing

spondyli-tis is a seronegative, chronic inflammatory disorder that affects the axial skeleton Changes in the spine (bamboo spine, trolley-track sign and squaring of vertebral bodies) are visible on radio-graphs and provide adequate diagnosis

Etiology: Ninety percent of patients with ankylosing

spondy-litis are HLA-B27 positive (Figure 11-4)

Figure 11-4 Bamboo spine AP radiograph of the spine.

ANTERIOR DRAWER SIGN3

Introduction and Anatomical Context: Anterior cruciate

ligament (ACL) runs obliquely within the lateral aspect of the

intercondylar notch, attaching to the intercondylar eminence

of the tibia distally

Etiology: Post-traumatic (Figure 11-3).

Figure 11-3 Anterior drawer sign (A) Sagittal

T2-weighted image of the knee shows anterior displacement

of tibia in relation to femur (double-headed arrow)

(B) Sagittal T2-weighted image of the knee shows ACL

tear (arrow)

A

B

Radiological Findings: Nearly complete fusion and squaring

of the vertebral bodies are noted Bony outgrowths give a

bamboo stalk appearance to the spine

Diagnosis: Ankylosing spondylitis.

Imaging Modality: Anteroposterior (AP) and lateral

radio-graphs

PEARLS

 Bony outgrowths in ankylosing spondylitis are due to

ossification of the annulus fibrosus

 Bridging osteophytes differentiate ankylosing

spondy-litis from diffuse idiopathic skeletal hyperostosis (DISH)

that has flowing osteophytes, small osteophytes in

degenerative joint disease, and large osteophytes in

psoriasis and reactive arthritis

BITE SIGN5

Introduction and Etiology: This sign is suggestive of

osteo-necrosis, avascular necrosis (AVN), or ischemic necrosis

Ischemia of the bone due to a variety of causes can lead to the

radiologic sign Ischemic insult can be due to reduced arterial

blood flow or venous insufficiency (Figure 11-5)

Radiological Findings: A small deformed femoral head is

shown with areas of osteolysis and sclerosis Punched out or

Figure 11-5 Bite sign AP radiograph of the hip

shows AVN of the femoral head with its lateral segment

missing

gouged out areas of bony destruction, similar to small animal bites, are typical of AVN This is secondary to repeated steroid injections

BLADE OF GRASS SIGN6,7

Introduction: Sign suggestive of osteolytic stage of Paget

disease

Etiology: Osteoclastic activity (Figure 11-6).

Radiological Findings: A well-demarcated radiolucent

V-shaped area in the diaphysis The lucency is extending caudally as a V-shaped or wedge-shaped radiolucent area, likened to a blade of grass

Diagnosis: Paget disease.

Imaging Modality: Radiograph and bone scan.

spi-Etiology: Expansile lytic lesion, primary in most cases

Thirty percent arise within existing bone tumors such as fibrous dysplasia, giant cell tumor, chondroblastoma, or osteoblastoma (Figure 11-7)

Radiological Findings: Frontal radiograph of the right hip

and CT scan of the proximal femora on a different patient

 CHAPTER 11

238

Figure 11-6 Blade of grass sign (A) AP radiograph of femur Arrows show advancing age of lesion (B) Anterior

view of bone scan in a different patient shows increased uptake in the distal left humerus due to Paget disease

Figure 11-7 Blister of bone sign in aneurysmal bone cyst (A) AP radiograph of femur with ABC (B) CT of left

femur in different patient with ABC

Both reveal a cystic and bubbly lesion with fine internal

sep-tations Cortical margin of the lesion is compromised The

bubbly, cystic lesion with a saccular cortical protrusion and

multiple internal septae produces a blister of bone sign,

highly characteristic of ABC

 ABC is eccentric in location, differentiating it from

unicameral bone cyst, which lies centrally in bone

metaphysis

BONE BRUISE SIGN8–10

Introduction and Anatomical Context: Bone bruise sign in

lateral femoral condyle and posterior tibial condyle with

anterior drawer sign is suggestive of bone trauma and ACL

tear

Etiology: Trauma leading to edema, hemorrhage,

microfrac-ture, and ACL tear (Figure 11-8)

Radiological Findings: T2-weighted image shows complete

ACL tear with mild increase in marrow signal on T2-weighted image in adjacent osseous tissue The bone bruises as evi-denced by increased signal are likely to be caused by impac-tion of middle and posterior portion of lateral tibial plateau Signal intensity abnormalities are probably secondary to edema, hemorrhage, and microfracture

Diagnosis: Indirect sign of bone trauma and ACL tear Imaging Modality: Sagittal fluid-sensitive MRI.

Introduction and Anatomical Context: A sign diagnostic of

osteopetrosis The bony change is best visualized on radiograph

Figure 11-8 Bone bruise sign (A) Bone edema (B) Bone edema and ACL tear (arrow).

 CHAPTER 11

240

Figure 11-9 Bone-in-bone sign, in osteopetrosis.

Etiology: Bone-in-bone sign results from failure of

osteo-clastic activity causing abnormally dense bone that occurs

intermittently producing zones of abnormal density

alternat-ing with relatively more normal ones (Figure 11-9)

Radiologic Findings: Lateral lumbar spine radiograph revealing

sclerosis in the superior and inferior portions of the midbody of the vertebra It gives the appearance of a small replica of the ver-tebral body inside the normal one, giving a bone-in-bone sign

BOUTONNIERE DEFORMITY12,13

Introduction and Anatomical Context: Boutonniere

defor-mity is the culmination of multiple osseous abnormalities in the hand in rheumatoid arthritis

Etiology: Inflammatory tear of the central slip of the extensor

tendon, which attaches to the middle phalanx (Figure 11-10)

Radiological Findings: Deformity of little finger noted with

hyperextension of distal interphalangeal joints and flexion at proximal interphalangeal joints

Diagnosis: Rheumatoid arthritis.

Imaging Modality: Radiograph.

PEARLS

Look for chip fracture fragment of the base of the dle phalanx, representing avulsion fracture by central slip of extensor tendon

Figure 11-10 Boutonniere deformity (A) Lateral radiograph of boutonniere deformity (B) Line drawing (Used with

permission from Arash Tehranzadeh, MD)

BOW TIE SIGN14,15

Normal bow tie is visible on sagittal MRIs in two consecutive

images only Either less or more images showing the bow tie

is abnormal

Etiology: Congenital, normal variant, and more prone to

injury ( Figure 11-11)

Radiological Findings: Bow tie appearance of the lateral

meniscus is seen on 3–5 consecutive, sagittal MRIs This

appearance is consistent with a discoid meniscus

Diagnosis: Discoid meniscus.

Imaging Modality: MRI.

PEARLS

 Excessive bow tie (3–5 consecutive, sagittal MRIs) is a

sign of discoid meniscus

 Lateral meniscus is less frequently injured as compared

with the medial meniscus due to its increased mobility

 Discoid meniscus is a normal variant of lateral

menis-cus and makes it more prone to injury

 Discoid meniscus can also be seen in the medial side

BRIM SIGN16

Introduction and Anatomical Context: Brim sign refers to

the pelvic brim, also known as the iliopectineal line

Etiology: Osteoblastic or bone forming stage of Paget

dis-ease Paget disease has four stages: osteolytic, osteosclerotic,

mixed, and malignant (Figure 11-12)

Radiological Findings: Patchy sclerosis of right hemipelvis is

seen Thickening of the right pelvic iliopectineal line (brim

sign) is visible compared with the left side

Diagnosis: Paget disease.

Imaging Modality: Radiograph.

Introduction and Anatomical Context: A sequestrum is a

small focus of calcification within a radiolucent area

Etiology: A sequestrum is a devascularized, necrotic piece

of bone secondary to a variety of pathological processes (Figure 11-13)

Radiological Findings: Single-slice CT scan of the pelvis

with an abnormal lucent area with a sclerotic focus in the left hemipelvis This sign was originally utilized to describe an unusual radiographic manifestation of eosinophilic granu-loma It is a round, lucent defect with a bony density, or sequestrum, in its center This is not pathognomonic as other

 CHAPTER 11

242

disease entities such as osteomyelitis, tuberculosis,

lym-phoma, and metastasis can have a similar appearance

Differential Diagnosis: Eosinophilic granuloma,

tuberculo-sis, lymphoma, metastatuberculo-sis, osteoid osteoma, chondroma,

chondroblastoma, and lipoma

Imaging Modality: CT scan.

PEARLS

 Button sequestrum is most commonly seen as a

cal-varial lesion

 This sign is not pathognomonic of eosinophilic

granu-loma, as it is also seen in osteomyelitis

C-SIGN18

Introduction and Anatomical Context: Subtalar coalition

presents most commonly as a flat foot and foot pain

Degen-erative osteoarthritic changes are common around the

abnormal bone bridge between the talus and the calcaneus

Etiology: Congenital anomaly (Figure 11-14).

Radiological Findings: Lateral radiograph of the foot

reveal-ing a classic C sign that is a C-shaped line formed by the

medial outline of the talar dome and the inferior outline of

the sustentaculum tali This sign is a reliable indicator of

sub-talar coalition on the lateral radiograph and represents the

bony bridge between the talar dome and the sustentaculum

tali

Diagnosis: Subtalar coalition.

Imaging Modality: Lateral radiograph.

PEARLS

C-sign is a reliable sign of subtalar coalition on lateral radiograph and represents a bony bridge between the talar dome and the sustentaculum tali

COCKADE SIGN19

Introduction and Anatomical Context: A cockade is a badge,

usually in the form of a rosette, or knot, and generally worn upon the hat

Etiology: Commonly seen in the proximal femur, fibula, and

calcaneus The lesion is usually asymptomatic and discovered incidentally on imaging (Figure 11-15)

Figure 11-13 Button sequestrum in child with

eosinophilic granuloma. coalition. Figure 11-14 C-Sign (arrows) indicating subtalar

Figure 11-15 Cockade sign indicating intraosseous

lipoma.

Radiological Findings: A classic appearance of intraosseous

lipoma of the calcaneus is the presence of a well-defined lytic

lesion with a central calcification resembling a cockade

Diagnosis: Intraosseous lipoma.

Imaging Modality: Radiograph.

PEARLS

 Intraosseous lipoma presents as an asymptomatic,

well-defined radiolucent osseous lesion with a central

calcified nidus

CORTICAL RING SIGN20 (SIGNET RING SIGN)

Introduction and Anatomical Context: This sign represents

scapholunate dissociation (stage I) It was first described in

1970 in a young patient with bilateral dislocation of the

car-pal navicular bones

Etiology: Post-traumatic (Figure 11-16).

Radiological Findings: Multiple images of navicular

disori-entation with subluxation of the scapholunate joint The

scaphoid bone, seen along its long axis, has a ringed cortex

appearance Cortical ring sign, also known as the signet ring

sign, indicates scapholunate dislocation and is caused by the

abnormal orientation of the scaphoid bone

Diagnosis: Rotary subluxation of scaphoid (scapholunate

disassociation)

Imaging Modality: Radiograph of wrist.

PEARLS

Cortical ring sign is seen on posteroanterior (PA) view

of the wrist, with a signet ring outline of the subluxed scaphoid

COTTON WOOL SIGN21

Introduction and Anatomical Context: Cotton wool sign is

a feature of the osteoblastic stage of Paget disease Osseous lesions are described in four different stages: osteolytic, scle-rotic, mixed, and malignant transformation

Etiology: Unknown (Figure 11-17).

Radiological Findings: Radiograph of the skull reveals a

large mottled area of increased radiodensity with small areas

of radiolucency within The MRI of the skull reveals a ened, enlarged cranium with increase in the marrow space Two bone scan images also reveal increased activity in the skull, more localized to one side, characteristic to the local-ized disease seen in Paget disease This is classic cranial involvement of Paget disease In the cranium, bone sclerosis may produce circular radiodense lesions in one area, whereas osteoporosis circumscripta is noted elsewhere In the skull, the common region of involvement is the cranial vault The osteolytic phase is called osteoporosis circumscripta and appears as multiple geographic, well-demarcated regions of bone resorption that may be mistaken for metastases Focal radiodensities occur as pagetoid bone is formed In the quies-cent phase, there is a radiodense cotton wool appearance with a thickened vault

thick-Diagnosis: Paget disease.

Imaging Modality: Radiograph, MRI, and bone scintigraphy.PEARLS

Although the pathological radiologic osseous changes

in the skull mimic osteoblastic metastases, the enlarged calvarium is a good sign of Paget disease

CRESCENT SIGN22

Introduction and Anatomical Context: Crescent sign is an

early diagnostic sign of AVN on radiographs It signifies a subcortical fracture of the femoral head

Etiology: Ischemia to the bone due to a wide variety of

causes The basic mechanism is reduced arterial blood flow

or venous insufficiency leading to osseous necrosis (Figure 11-18)

Figure 11-16 Cortical ring sign, or signet ring sign,

indicating scapholunate dissociation.

Figure 11-17 Cotton wool sign indicating Paget

disease (A) Radiograph of skull with Paget disease

(B) MRI with Paget disease (C) Bone scan of skull with

Radiological Findings: A radiograph of a left hip joint,

which reveals a thin, curvilinear lucent line parallel to the

cortical margin (18A, arrow) of the femoral head

Interrup-tion of the blood supply to the femoral head leads to ischemic

necrosis of the marrow and bone that it supplies Eventually,

bone infarcts and insufficiency fractures may ensue

Frac-tures that occur in the subchondral bone may be recognized

by a crescentic lucent zone that separates the fragment from

the remainder of the femur

Diagnosis: AVN.

Imaging Modality: Radiograph and MRI.

PEARLS

 Look for a crescentic lucent zone, separating the

frac-ture fragment from the adjacent bone

 MRI is the imaging modality of choice with 100%

sen-sitivity

CROWDED CARPAL SIGN23

Introduction and Anatomical Context: To understand the

carpal dislocation, recall the three carpal arcs The first arc is

a line traced along the proximal carpal row, proximally The

second carpal arc is drawn along the proximal carpal row

dis-tally and the third arc is drawn along the distal carpal row,

distally In crowded carpal sign, the first and second arcs are

no longer distinct

Etiology: Post-traumatic (Figure 11-19).

Radiological Findings: Frontal radiograph of the wrist

reveals overlap of the distal carpal row with the proximal pal row This overriding gives rise to the “crowded carpal” appearance and is a sign specific for volar perilunate disloca-tion It is secondary to proximal migration of the distal row

car-of carpal bones during subluxation

Diagnosis: Volar perilunar dislocation.

Imaging Modality: Radiograph.

PEARLS

Failure to delineate proximal carpal row from the distal carpal row with loss of visualization of first and second carpal arcs indicating volar perilunar dislocation

CUPID’S BOW SIGN24

Introduction and Anatomical Context: Normal variants are

important to recognize to avoid labeling the observation as pathological

Etiology: Normal variant (Figure 11-20).

Radiological Findings: Frontal and lateral radiograph of the

lumbar spine with curvature of the inferior endplates of the fourth and fifth lumbar vertebrae, mimicking the curvature

of Cupid’s bow aimed cephalad The unusual, non-flat face of the inferior endplate is a normal variant, and need not be misinterpreted as inherent osseous abnormality or adjacent pathological process

sur-Diagnosis: Normal spine.

Imaging Modality: Radiograph.

PEARLS

Normal variant not to be misinterpreted as inherent osseous abnormality or a sign of pathological process

DAGGER SIGNIntroduction and Anatomical Context: Ankylosing spondy-

litis is a chronic inflammatory disorder affecting the spine and sacroiliac joints Ninety percent of the patients are HLA-B27 positive

Etiology: Ossification of the interspinous and supraspinous

ligaments (Figure 11-21)

Figure 11-19 Crowded carpal sign indicating volar

perilunar dislocation There is an associated

nondis-placed ulnar styloid fracture

indicat-(C) Cupid drawing (Used with permission

from Arash Tehranzadeh, MD)

Radiological Findings: Single frontal radiograph of the

bar spine in a patient with bony fusion of the adjacent

lum-bar vertebrae with syndesmophyte formation, characteristic

for ankylosing spondylitis In addition, there is a linear

increased density running along the spinous processes The

dagger sign is a single central radiodense line on frontal

radiographs related to ossification of supraspinous and

inter-spinous ligaments Note bilateral symmetrical fusion of

sacroiliac joints

Diagnosis: Ankylosing spondylitis.

Imaging Modality: Radiograph.

PEARLS

Squaring of vertebral bodies, ossification of nous, and supraspinous ligaments (dagger sign) are pathognomonic of ankylosing spondylitis

interspi-DEEP LATERAL FEMORAL NOTCH SIGN25,26

(DEEP SULCUS SIGN)

Introduction and Anatomical Context: The deep femoral

notch sign is a secondary sign of ACL tear It is due to an

impacted fracture of the lateral sulcus, similar to the Hill–

Sachs lesion of the humerus

Etiology: Post-traumatic (Figure 11-22).

Radiological Findings: The deep lateral femoral notch

(sul-cus) sign is used as a secondary sign of ACL tear The increased

depth of the lateral femoral sulcus in patients with an ACL tear

is due to an impacted fracture This impaction occurs when the

tibia becomes displaced anteriorly and the lateral femoral

sul-cus pushes against the posterior rim of the tibial plateau,

caus-ing an indentation in the femoral condyle It is measured by

drawing a line drawn tangential to the articular surface of the

fem-oral condyle This line is used as a reference and the depth of the

sulcus is measured perpendicular to this line Abnormally increased

depth is known as the deep lateral femoral notch (sulcus)

Imaging Modality: Radiograph and MRI.

Diagnosis: ACL tear.

PEARLS

Indirect sign of ACL tear

DOUBLE PCL SIGN27,28

Introduction and Anatomical Context: Injury to the menisci

can result in the meniscus being torn in the shape of a bucket and its handle This sign refers to the peripheral (bucket) part of the meniscus and displaced inner fragment (handle) portion

Etiology: Post-traumatic (Figure 11-23).

Radiological Findings: Sagittal T2-weighted MRI of the

knee through the intercondylar notch reveals a fragment of torn meniscus that appears as low-signal intensity longitu-dinally oriented band lying beneath and parallel to the PCL, creating a double cruciate configuration, referred to as the double PCL sign This inner fragment or “handle” can be displaced for a variable distance over the tibial plateau sur-face If displaced as far as the intercondylar notch, in case of medial meniscus the inner fragment can come to lie between the PCL and the underlying tibia

Imaging Modality: MRI.

Diagnosis: Bucket handle tear of the meniscus.

PEARLS

Bucket handle tear of the meniscus can mimic a PCL in location, shape, and signal intensity When identified, this sign signifies meniscal injury

DROOPING SHOULDER SIGN29

Introduction and Anatomical Context: The drooping

shoul-der is a loss of the normal contour of the shoulshoul-der on AP graph as the normal bone alignment is lost

radio-Etiology: The drooping shoulder occurs following fracture

of the surgical neck and may be secondary to hemarthrosis or musculoligamentous injury Other nontraumatic causes such

as stroke and brachial plexus compromise from a tumor have been described as well (Figure 11-24)

Radiological Findings: Two views of the right shoulder in

this post-traumatic patient with a fracture of the proximal humerus Note the downward displacement of the humerus and its relation to the acromioclavicular joint and the glenoid

Figure 11-21 Dagger sign indicating ankylosing

spondylitis.

 CHAPTER 11

248

Diagnosis: Inferior subluxation of the shoulder.

Imaging Modality: Radiograph.

PEARLS

 Fracture surgical neck of the humerus with downward

displaced head of humerus and widened

glenohu-meral space

DRUNKEN WAITER SIGN30

Introduction and Anatomical Context: Normally, the

sus-tentaculum tali joint has a horizontal alignment in coronal images of the ankle An oblique orientation of this joint mimics the tilted tray of a drunken waiter and suggests sub-talar coalition

Etiology: Congenital (Figure 11-25).

A

C

B

Figure 11-22 Deep sulcus sign indicating ACL tear

(A) Lateral radiograph with arrow pointing to deep sulcus (B) Sagittal spin echo T2 MRI with arrow pointing to deep sul- cus (C) Fluid-sensitive MRI with arrow pointing to torn ACL.

Figure 11-23 Double PCL sign indicating bucket

handle tear of the meniscus (arrow).

Figure 11-24 Drooping shoulder sign indicating

inferior shoulder subluxation.

Figure 11-25 Drunken

waiter sign (A) Coronal

reformatted CT shows tilted

sustentaculum tali joint

indi-cating fibrous coalition at the

mid subtalar joint (B)

Drunken waiter drawing

(Used with permission from

Arash Tehranzadeh, MD)

 CHAPTER 11

250

fat pad sign (Figure 11-26B, arrows) Injuries that produce intra-articular hemorrhage cause distension of the synovium and force the fat out of the fossa, producing triangular radio-lucent shadows anterior (“sail sign”) and posterior to the dis-tal end of the humerus When present in a patient with a history of acute trauma to the elbow, the fat pad sign indi-cates the presence of an intra-articular hemorrhage, which in turn is often associated with an intra-articular skeletal injury (usually radial head fracture in an adult)

Diagnosis: Elbow joint effusion.

Imaging modality: Radiograph.

PEARLS

Elbow fat pad sign is an invaluable sign of lar effusion following elbow injury

intra-articu-FALLEN FRAGMENT SIGN34–36

Introduction and Anatomical Context: ∗A bone cyst leads to cortical expansion, thinning, and pathological cortical fracture

Etiology: Pathological fracture (Figure 11-27).

Radiological Findings: Two radiographs of a pathological

fracture in a simple bone cyst of the proximal humerus

Radiological Findings: Coronal images of CT or MRI

show-ing tilted alignment of the mid subtalar joint (sustentaculum

tali joint) would indicate coalition of the subtalar joint at this

level The coalition could be fibrous cartilaginous or bony

Diagnosis: Subtalar joint coalition.

Imaging Modality: CT and MRI.

PEARLS

 Tilted mid subtalar joint on coronal images of CT or MRI

mimicking the tilted tray of a drunken waiter is

indica-tive of subtalar joint coalition

ELBOW FAT PAD SIGN31–33

Introduction and Anatomical Context: Fat is normally

pres-ent within the joint capsule of the elbow, but outside the

synovium Typically “hidden” in the concavity of the

olecra-non and coronoid fossae, the fat is usually not visible on the

lateral radiograph

Etiology: Post-traumatic (Figure 11-26).

Radiological Findings: Comparative radiographs showing a

normal lateral radiograph of the elbow (Figure 11-26A) and

a lateral radiograph of the elbow showing the classic elbow

Figure 11-26 Elbow fat pad sign showing elbow joint effusion (A) Arrows showing normal fat pad (B) Arrow

showing anterior “sail” sign indicating elbow joint effusion