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Patel-lofemoral instability, component dissociation or loosening, patellar fracture, residual anterior knee pain, component wear, osteonecrosis, patellar Òclunk,Ó and patellar ten-don ru

Patients who have undergone total

knee arthroplasties are enjoying

pro-longed success of the procedure well

into the second decade, with

pros-thetic survivorship in excess of 90%

at 10 to 15 years Despite these

predictable results, a number of

complications continue to plague

patient and surgeon alike These fall

into three major groups: extensor

mechanism complications, other

mechanical complications, and

regional or systemic complications

Understanding the incidence and

etiology of these problems enhances

the surgeonÕs ability to avoid them

during the primary surgical

proce-dure With careful assessment of the

symptomatic knee and an

under-standing of the effectiveness of

sal-vage procedures, one can generally

achieve a satisfactory result

Extensor Mechanism

Complications

Over the past three decades, the

in-cidence of extensor mechanism

complications has decreased from approximately 12% to 1.5% as a result of design modifications, tech-nical advancements in attaining proper rotational and axial align-ment of the individual components, and improvements in soft-tissue bal-ancing.1-3 Nonetheless, the patello-femoral joint remains the most com-mon source of pain and dysfunction after total knee arthroplasty Patel-lofemoral instability, component dissociation or loosening, patellar fracture, residual anterior knee pain, component wear, osteonecrosis, patellar Òclunk,Ó and patellar ten-don rupture account for up to 50%

of secondary surgical procedures after total knee arthroplasty.1,2

Patellofemoral Instability

Patellar instability is the most common reason for secondary sur-gery after total knee arthroplasty

The reported incidence of patellar maltracking (tilting, subluxation, or dislocation) varies from 0.5% to as high as 29%.1,3 Patellar maltrack-ing may be related to prosthetic

design, extensor mechanism imbal-ance, asymmetric patellar resection, malrotation of the femoral or tibial component, or patellar malposi-tioning

Component design is important for stable patellar tracking To accommodate either a resurfaced

or a nonresurfaced patella, the femoral component should ideally have a broad trochlear groove that extends proximally to accommo-date the patella in full extension The trochlea should be directed toward the lateral side to engage the patella early in flexion Dis-tally, patellar tracking is enhanced when the trochlear groove is nar-rowed and deepened to contain the patella, limiting lateral subluxation

in flexion.4 Patellar views of the implant will display patellar com-ponent subluxation (Fig 1) Theiss

Dr Lonner is Assistant Professor, Department

of Orthopaedic Surgery, University of Penn-sylvania School of Medicine, Philadelphia Dr Lotke is Professor of Orthopaedic Surgery, University of Pennsylvania School of Medicine Reprint requests: Dr Lonner, Department of Orthopaedic Surgery, Hospital of the Univer-sity of Pennsylvania, 2 Silverstein, 3400 Spruce Street, Philadelphia, PA 19104 The authors or the departments with which they are affiliated have received something of value from a commercial or other party related directly or indirectly to the subject of this arti-cle.

Copyright 1999 by the American Academy of Orthopaedic Surgeons.

Abstract

Aseptic complications after total knee arthroplasty are occurring less frequently

than they did one or two decades ago This is related in part to technical

advancements, design improvements, and changes in perioperative

manage-ment Extensor mechanism dysfunction is the most frequent complication and

the most commonly cited reason for secondary surgery after total knee

arthro-plasty Mechanical wear, tibiofemoral instability, periprosthetic fracture,

thromboembolic disease, compromised wound healing, neurovascular problems,

and stiffness are less common, but nevertheless troublesome, sources of

dysfunc-tion after total knee arthroplasty Complicadysfunc-tions compromise outcomes, and the

most effective way of dealing with complications is prevention.

J Am Acad Orthop Surg 1999;7:311-324

Jess H Lonner, MD, and Paul A Lotke, MD

et al5evaluated the data on total

knee arthroplasties performed with

implants of two different designs

and found that the results were

comparable except for the

inci-dence of postoperative

patello-femoral complications (10% for one

design and 0.7% for the other)

They attributed this disparity to the

striking differences in femoral

com-ponent morphology between the

two designs

Patellar component design (e.g.,

dome-shaped buttons, ÒMexican

hatÓÐlike buttons, and asymmetric

components), medialization of the

component to approximate the

anatomic center axis,6 the accuracy

and extent of patellar bone

resec-tion, and restoration of patellar

thickness may all affect patellar

tracking Excessive resection of the

patella so that the remaining

thick-ness is less than 10 to 15 mm may

predispose it to fracture;

insuffi-cient resection may limit flexion

and contribute to maltracking.7

Proper tracking requires a

nor-mal Q angle, which is affected by

the axial and rotational alignment

of the femur and tibia An

exces-sive Q angle may result from

medi-alization of the tibial tray, excessive

valgus alignment of components,

or internal rotation of either

com-ponent Patellofemoral

maltrack-ing may also result from soft-tissue

imbalance if the lateral retinaculum

is contracted or the medial retinac-ular sleeve is lax

Correct axial femoral component alignment, perpendicular to the mechanical axis, is paramount to prevention of patellar maltracking

The femoral component should also be implanted with enough external rotation to establish a rec-tangular flexion gap and to facili-tate patellar tracking In addition,

it should be appropriately sized in the anteroposterior dimension to avoid ÒoverstuffingÓ the patello-femoral compartment

A variety of methods have been developed for determining the appropriate rotational alignment of the femoral component (Fig 2).8

Using the posterior femoral con-dyles as a reference, the examiner should assess the knee for severe deformity or condylar hypoplasia

In the presence of severe valgus deformity, deficiency of the poste-rior lateral femoral condyle may erroneously place the cutting jig in relative internal rotation Proper rotation of the tibial component, so that its center is in line with the medial third of the tibial tubercle, and avoidance of medialization of the tibial component will enhance patellar tracking (Fig 3)

Patellar tracking is most

accurate-ly assessed with the tourniquet deflated, to eliminate the binding effect of the tourniquet on the quadriceps Without closing of the medial retinaculum or forcing of the patella medially (Òthe rule of no thumbsÓ), the patella should track congruently within the trochlear groove without tilting or subluxat-ing If the patella tilts or subluxates,

a lateral retinacular release should

be performed If patellar subluxa-tion still occurs, rotasubluxa-tion, alignment, patellar composite thickness, and button position should be evaluated

Treatment of patellar maltracking

is based on the cause of the insta-bility Nonsurgical treatments for

patellar subluxation or dislocation are generally unsuccessful Surgery must be directed at the underlying cause of the problem In the absence

of component malpositioning, a lat-eral retinacular release may be all that is necessary to improve patellar tracking A lateral retinacular re-lease is performed from the inside out in an attempt to preserve the blood supply of the skin flap as well

as the lateral superior genicular ves-sels Distal to the vessels, the lateral retinaculum is released in a direc-tion perpendicular to the joint line Proximally, an oblique limb is directed 45 degrees anteriorly, relieving lateral traction by the ilio-tibial band in flexion.9 Distal realignment involving tibial tubercle osteotomy has been advocated, par-ticularly when an excessive Q angle

is present.10 However, when there

is significant component malalign-ment, tubercle osteotomy is less effective than component revision

Fig 1 Patellar view showing patellar

sub-luxation and tilt Note the asymmetric

patellar osteotomy.

Fig 2 Four reference lines used in deter-mining femoral component external rota-tion: AP = anteroposterior axis; PCA = pos-terior condylar axis; TEA = transepicondylar axis; TFG = tensioned flexion gap Gener-ally, a balanced flexion gap will be created

by resecting the posterior femoral condyles parallel to the TEA, perpendicular to the AP axis, 3 degrees externally rotated from the PCA, or parallel to the proximal tibia with the balanced collateral ligaments tensioned (as reflected by the TFG).

Medial

PCA

Lateral

TEA AP

3° TFG

Patellar Fracture

Patellar fracture after total knee

arthroplasty has a variety of causes,

including abnormal stress

concen-trations, osteonecrosis, and patella

baja The patella is susceptible to

failure when the bone has been

weakened and high stresses are

applied Direct trauma to the

pa-tella after total knee arthroplasty is

uncommon Compressive loads

across the patellofemoral

articula-tion approach four to seven times

body weight in certain activities,

such as squatting and stair descent

Furthermore, when the transition

zone between the trochlear region

and the condylar region of the

fe-moral component is abrupt, the

localized stress concentration can be

quite severe Overstuffing the

patellofemoral joint with an

over-sized femoral component, an

anteri-orly offset femoral component, or a

femoral component placed in

exces-sive extension can also overload the

patella A similar phenomenon may

be seen with insufficient resection of

the patella or use of a thick button

Excessive patellar resection can

predispose to patellar fracture as

well Reuben et al7have

demon-strated that a residual patellar

thickness of less than 15 mm can

substantially increase anterior

patellar strain

Osteonecrosis of the patella may

lead to late fracture and

fragmenta-tion of the patella (Fig 4) Anatomic studies of patellar blood supply have mapped out an extensive sys-tem of both extraosseous and in-traosseous arterial systems There are contributions from all the genic-ular vessels (Fig 5) Each of these vessels is potentially at risk during the surgical approach, soft-tissue dissection, and subsequent patellar resurfacing The standard medial parapatellar arthrotomy will divide the superior and inferior genicular arteries as well as the descending genicular artery Additionally, the lateral inferior genicular artery is commonly sacrificed during lateral meniscectomy When a lateral reti-nacular release is subsequently per-formed, the lateral superior genicu-lar artery is at risk, particugenicu-larly when not dissected free and protected

Aggressive resection of the infra-patellar fat pad can theoretically compromise the traversing branches that supply the inferior pole of the patella However, this has not re-sulted in an obvious decrease in pa-tellar perfusion.11 Diminished pa-tellar vascularity has been observed acutely on technetium bone scans, but follow-up studies suggest that patellar revascularization may occur

as early as 60 days after the surgical procedure.12

Elevation of the tibiofemoral joint line as a result of proximal femoral resection and posterior cruciate liga-ment release will cause relative

patel-la baja This creates a nonanatomic patellofemoral articulation, which may result in patellar impingement

on the tibial insert in late flexion and ultimately in patellar fracture Con-sidering the proximal shift in the joint line seen with standard posteri-orly stabilized total knee arthroplas-ties, it has been postulated that there may be a higher risk of patellar frac-ture with these implants.13

Treatment of patellar fractures is dependent on fracture pattern, loca-tion, remaining bone stock,

integri-ty of the component-cement-bone

interface, and competence of the extensor mechanism The classifi-cation by Goldberg et al14is helpful for planning appropriate interven-tion Type I fractures are avulsion-type fractures, generally involving the periphery of the patella but not the implant, cement, or quadriceps mechanism Type II fractures dis-rupt the cement-prosthesis inter-faces or the quadriceps mechanism Type III-A fractures involve the in-ferior pole of the patella with disrup-tion of the patellar ligament Type III-B are nondisplaced fractures of the inferior pole of the patella with

an intact patellar ligament Type IV fractures are fracture-dislocations of the patella

Nonoperative treatment is pre-ferred when fractures are nondis-placed.14-16 Unfortunately, the defi-nition of displacement used in the literature has varied from 2 mm to 2

cm, and clinical experience in treat-ing patellar fractures after total knee arthroplasty has generally been

Fig 3 The appropriate technique for

aligning the tibial component is to rotate it

so that its center is in line with the medial

third of the tibial tubercle.

Fig 4 Lateral radiograph of a knee after total knee arthroplasty Note displaced fracture of the inferior pole of an osteo-necrotic patella The patellar component had been removed 1 year earlier because of dissociation.

anecdotal Hozack et al15reviewed

21 patellar fractures after total knee

arthroplasty Nonoperative

treat-ment of nondisplaced or minimally

displaced fractures (6 to 8 weeks of

cast immobilization) yielded

satis-factory results The results of

surgi-cal treatment were variable, but

more predictable outcomes were

associated with partial or complete

patellectomy than with attempted

open reduction and internal

fixa-tion Goldberg et al14reported

com-parable results in their experience

treating 36 patellar fractures after

total knee arthroplasty Type I

frac-tures, which had been treated in a

cast in extension, had satisfactory

results Unfortunately, fracture

pat-terns categorized as types II, III-A,

or IV generally had unsatisfactory

outcomes despite surgical interven-tion and appropriate postoperative physical therapy

Windsor et al16 noted that com-minuted patellar fractures, regardless

of the extent of fragment displace-ment, can be treated in a cylinder cast, unless there is compromise of the prosthesis-patella composite In the latter scenario, a patellectomy has better results than attempted open reduction and internal fixation, which may predispose the patella to osteonecrosis or nonunion Another option for these comminuted frac-tures is to remove the patellar ponent and allow healing of the com-minuted bone fragments in a cast

Transverse fractures with displace-ment by more than 1 cm and/or an extensor lag greater than 30 degrees

may be treated with cerclage tension-band wiring, provided the patellar component is intact and the native bone stock is adequate Otherwise, patellectomy is preferable.15

Displaced avulsion fractures of either the proximal or the distal pole

of the patella with an intact patellar component and a viable patella can

be stabilized with heavy nonab-sorbable sutures passed through the quadriceps tendon or patellar ten-don and secured to the patella through drill holes To protect the repair, a checkrein-type figure-of-eight stitch may be tied over the anterior aspect of the extensor mech-anism After fixation, patellar track-ing and component stability should

be assessed Postoperatively, pas-sive knee motion may be allowed

Patellar Tendon Rupture

Rupture of the patellar tendon after total knee arthroplasty is un-common, occurring in 0.17% to 1.45% of cases.2,17 This injury can be devastating for the patient, as the results of treatment are frequently suboptimal The most common cause of extensor mechanism dis-ruption is intraoperative tendon avulsion off the tibial tubercle that occurs when excessive tension is used when trying to obtain adequate exposure Late rupture may result from manipulation, distal tubercle realignment procedures, direct

trau-ma, or impingement on the tibial insert

Considering the relatively poor results of treatment of this compli-cation, even with surgical interven-tion, it is preferable to be extremely careful when handling the tendon at the time of primary arthroplasty A knee with limited motion or intra-articular scarring, pintra-articularly when associated with patella baja, is at greater risk When exposure is diffi-cult, graduated extensile exposure is initiated with posteromedial dissec-tion and external tibial rotadissec-tion If necessary, a modified quadriceps

Fig 5 Left,The peripatellar extraosseous anastomotic ring is composed of six arteries:

descending genicular (DG), medial superior genicular (MSG), medial inferior genicular

(MIG), lateral superior genicular (LSG), lateral inferior genicular (LIG), and anterior tibial

recurrent (ATR) Right, The three intraosseous zones of patellar blood supply are the

quadriceps tendon supply (QT) proximally, the midpatellar supply (MP), and the polar

supply (P) distally.

LSG

LIG

ATR

DG

MSG

MIG

QT

MP P

V-plasty, quadriceps snip, or tibial

tubercle osteotomy should be

con-sidered to protect the patellar

ten-don insertion In addition, a pin or

drill bit may be inserted into the

dis-tal patellar tendon insertion to

pro-tect it from avulsing Manipulation

of a stiff knee under anesthesia may

be complicated by rupture of the

patellar tendon or supracondylar

fracture of the femur The risk of

these complications can be reduced,

in part, by performing manipulation

within 6 weeks of arthroplasty

If distal ligament avulsions

involve less than 30% of the tibial

tubercle insertion, a primary repair

of the medial capsuloretinacular

sleeve should suffice, without any

need for alteration in normal

post-operative physical therapy For

complete avulsions, primary

reat-tachment has been relatively

un-successful, with a high incidence of

rerupture and functional

impair-ment.17

Primary suture repair of attri-tional or traumatic ruptures is typi-cally ineffective In general, there are two methods of patellar tendon reconstruction that may be effective

in these circumstances The deci-sion of which to use is influenced

by the quality of the remaining native patellar bone stock When there is adequate patellar bone stock, primary repair and augmen-tation with an autogenous semi-tendinosus graft is effective With the technique modified from Cadambi and Engh18and Ecker et

al,19the standard total knee incision can be used to harvest the semi-tendinosus, leaving its insertion point on the pes anserinus intact

The attached graft is then routed proximally along the medial aspect

of the patellar tendon, passed trans-versely through the patella, and sutured back to its pes anserinus insertion Postoperatively, the knee

is immobilized in extension for 6 to

8 weeks before progressive rehabili-tation is started

An extensor mechanism allograft can be considered when the patellar bone stock and soft tissue are defi-cient (Fig 6) Emerson et al20 re-ported satisfactory results with the use of an allograft quadriceps ten-don, patella, patellar tenten-don, and tibial tubercle bone block The allo-graft tibial tubercle is fitted into a trough in the tibial tubercle, placed

so that the patella will be positioned appropriately with respect to the joint line, and is then secured with screws The patella may or may not

be resurfaced The quadriceps com-ponent of the allograft is tensioned and secured to the host quadriceps tendon with nonabsorbable sutures The graft should have a moderate amount of tension with the knee fully extended, allowing approxi-mately 60 to 70 degrees of flexion against gravity The native host tis-sues are sutured over the allograft to

Fig 6 A, Lateral radiograph shows patella alta due to insufficiency of the patellar tendon after total knee arthroplasty B, Intraoperative

photograph of an implanted extensor mechanism allograft in a patient with patellar tendon rupture and inadequate patellar bone stock The tibial trough is made after establishing the appropriate position of the patella relative to the joint line The bone plug is secured with one or two cortical screws The allograft is sutured peripherally to the remaining undersurface of the host extensor mechanism with

non-absorbable suture The native tissues are then closed over the allograft C, Postoperative lateral radiograph after reconstruction The

allo-graft patella was not resurfaced.

minimize the risk of soft-tissue

slough and to promote healing

Postoperatively, passive

range-of-motion exercises may begin

immedi-ately Progressive rehabilitation

should be initiated carefully

Al-though the 2-year results with this

technique are encouraging,

longer-term follow-up is necessary.20

Soft-Tissue Impingement

The Òpatellar clunk syndromeÓ

occurs when a fibrous nodule or

proliferative synovium forms at the

insertion of the quadriceps tendon

and impinges on the patella.21 The

symptoms include snapping, pain,

crepitus, and sometimes secondary

patellar instability This condition

occurs almost exclusively in

pa-tients with posteriorly stabilized

implants The fibrous nodule may

lodge within the intercondylar

notch of the femoral component in

flexion and catch on the femoral

component as the knee proceeds

into extension, causing the

charac-teristic symptoms

When a posteriorly stabilized

knee prosthesis is used, the

peri-patellar synovium around the quad-riceps tendon insertion should be excised (Fig 7) The prosthesis de-sign may also play a role in the development of patellar clunk syn-drome Newer femoral components have a lower box and a more poste-rior position of the femoral cam, which minimizes the risk of soft-tissue impingement within the box

Nonoperative treatment of early patellar clunk syndrome or retro-patellar scarring should include a trial of anti-inflammatory medica-tions Use of intra-articular cortico-steroid injections after total knee arthroplasty is ill advised In the event that nonoperative measures fail to adequately relieve the pa-tientÕs symptoms, arthroscopic debridement or arthrotomy with debridement and excision of hyper-trophic tissue is recommended

Arthroscopic debridement is effec-tive; however, care must be taken

to avoid scratching the implants

Arthrotomy may be necessary if extremely dense peripatellar adhe-sions make arthroscopic visualiza-tion difficult

Patellar Component Wear and Loosening

Patellar component wear is com-mon, but loosening of the patellar component is uncommon, report-edly occurring in approximately 1% of cases.1 Considering the high compressive shear stresses trans-mitted across the patellofemoral articulation, it is surprising that the incidence of loosening of patellar components is not higher Risk fac-tors for patellar component loosen-ing or dissociation include deficient bone stock, component malposi-tioning, patellar maltracking, patel-lar osteonecrosis, asymmetric bone resection, altered joint line, osteoly-sis due to reaction to metal debris, failure of bone ingrowth in porous-coated designs, and obesity Metal backing was introduced to help dissipate joint contact forces Unfortunately, metal-backed implants commonly failed because of failure of bone ingrowth, delamination of the polyethylene from the metal backing, and rapid polyethylene wear, with subsequent metal-on-metal contact and generation of metallic debris

Fig 7 A,Arthroscopic view shows hypertrophic synovium on the posterior aspect of the quadriceps tendon, impinging within the

inter-condylar housing of the femoral component beyond 70 degrees of flexion B, Impingement of the scar was eliminated after arthroscopic

excision of the hypertrophic tissue.

Failure of the patellar

compo-nent may present with a variety of

symptoms, ranging from a painless

effusion to retropatellar pain,

click-ing, or instability Radiographic

findings may be subtle, although

the outline of a dissociated patellar

component may be visualized on a

Merchant view, or thinning of the

polyethylene may be seen In cases

of failure of a metal-backed

compo-nent, the metal base plate may be

seen articulating with the femoral

component, or metallic stippling

within the soft tissues (Òmetallic

synovitisÓ) may be seen

Failed Patellar Component

Revision of a failed patellar

pros-thesis can be difficult and must be

individualized, depending on the

remaining patellar bone stock and

the condition of the articulating

femoral component If the native

patellar bone stock is insufficient,

either patellaplasty or patellectomy

should be considered Resurfacing

of an inadequate patella may result

in osteonecrosis or fracture Isolated

patellar component revision has

yielded mixed results, with high

complication rates Berry and Rand22

reported good or excellent results in

30 of 36 knees (83%) at follow-up 2

to 8 years after isolated patellar

ponent revision Nonetheless,

com-plications were observed in 14 of 36

knees (39%) Failure of a

metal-backed patellar component may

result in burnishing or scoring of the

femoral component, necessitating its

revision as well Thorough joint

debridement to remove the

metal-stained synovium and inspection of

the implant-bone interfaces are

nec-essary to ensure that significant

oste-olysis or loosening has not occurred

Tibiofemoral Flexion

Instability

Equal flexion and extension spaces

are critical to ensure stability and

pre-vent postoperative subluxation

Tibiofemoral instability in flexion may occur in the immediate postop-erative period, or it may have a de-layed onset There are several poten-tial causes of this problem, including excessive recession or delayed in-competence of the posterior cruciate ligament in cruciate-retaining knee implants, excessive resection of the posterior femoral condyles, asymme-try of the flexion space, incompetence

of the medial collateral ligament, or overzealous release of soft-tissue restraints Late polyethylene wear of the tibial insert may create further instability in flexion Rupture of the extensor mechanism may result in posterior instability

Treatment of prosthetic knee-joint instability must be predicated on its origin Sacrificing the posterior cru-ciate ligament will enlarge the flex-ion space, which does not routinely occur with cruciate retention There-fore, the distal femoral osteotomy is usually made 2 to 3 mm more prox-imally relative to the trochlear groove Resection of the distal femur to the level of the trochlear notch will create equal flexion and ex-tension gaps in cruciate-substituting total knee arthroplasties Although this may elevate the joint line by

2 to 4 mm in balanced posterior-substituting total knee arthroplas-ties, it is unavoidable; fortunately, it

is generally well tolerated

When posterior cruciate liga-ment recession is necessary for placement of cruciate-retaining implants, one must carefully assess the integrity of the ligament at the termination of the procedure Com-plete recession of the posterior cru-ciate ligament in the setting of severe varus or valgus deformity should not cause instability if a curved tibial insert is utilized.23

However, rupture of an attenuated posterior cruciate ligament, as has been observed in patients with rheumatoid arthritis, may result in delayed instability in flexion.24

Medial-lateral imbalance of the flexion space may result from either rotational malalignment of the femoral component or dynamic imbalance created by soft-tissue re-leases A trapezoidal flexion space may cause asymmetric flexion in-stability Femoral component rota-tion is an important factor Soft-tissue releases must then be appro-priately tailored so that the medial and lateral compartments are well balanced in flexion and extension Residual medial-compartment in-stability may be treated with a con-strained condylar-type implant, which will provide not only an-teroposterior stability but also medial-lateral stability If there is insufficiency of the medial

collater-al ligament, reconstruction may be necessary A variety of techniques may be used, such as reconstruct-ing the ligament with a harvested looped semitendinosus autograft left intact at the pes anserinus in-sertion distally and then attached

to the medial femoral epicondyle with a screw and soft-tissue washer The reconstruction is augmented with a constrained condylar-type implant (Fig 8)

When delayed flexion

instabili-ty occurs as a consequence of late posterior cruciate ligament failure

or polyethylene wear, changing to

a thicker insert may be adequate

to address the problem In that situation, an insert with sagittally curved topography should be utilized If significant flexion instability persists, revision to a posterior stabilized implant is recommended

Wound Complications

Compromised wound healing may increase the risk of infection and subsequent failure The vascular anatomy of the knee, biomechani-cal factors, selection of surgibiomechani-cal incisions, surgical technique, and

patient-related risk factors must all

be considered when evaluating

wound healing

Vascular Anatomy

The blood supply to the soft

tis-sues of the anterior aspect of the

knee is relatively random and

inconsistent, with contributions

from the terminal branches of the

peripatellar anastomotic arterial

ring Because there is no muscle

beneath the skin and soft tissues of

this region of the knee, perfusion is

sparse.25 The dermal plexus, which

is composed of arterioles traveling

within the subcutaneous fascia, is responsible for providing skin cir-culation Therefore, elevation of skin flaps in the anterior aspect of the knee for exposure must be deep

to the subcutaneous fascia to pre-serve the critical and often tenuous blood supply to the skin

Biomechanical Factors

Biomechanical factors, such as surgical trauma, skin tension, ori-entation of skin incisions, early mobilization, and tissue oxygen tension, are important considera-tions as well Making a surgical

incision induces relative tissue hypoxia The decline in oxygena-tion in the skin is dramatic, with a 67% decrease observed during the first postoperative day By 8 days after surgery, the decrease in oxy-genation is only 16%.26

Considering the relative hypoxia

of the lateral skin margin, a medial parapatellar skin incision is relatively undesirable, as it will create a large lateral skin flap with diminished oxygenation.25 A midline incision is preferred for primary surgery; how-ever, a preexisting surgical incision should be incorporated whenever

Fig 8 A and B, Anteroposterior and lateral

radio-graphs of a patient with pain and instability due to malalignment of a total knee arthroplasty with laxity

of the medial collateral ligament Note the posterior tibiofemoral contact point At the time of surgery, the medial collateral ligament was noted to be

incompe-tent C and D, Intraoperative photographs of

recon-struction of the medial collateral ligament with the use of looped semitendinosus tendon autograft

E and F, Postoperative radiographs show revised total

knee components and medial collateral ligament reconstruction.

possible If that is not feasible, the

new incision should be parallel to

the existing one, producing a

bipedi-cle flap; the ratio between the width

between incisions and the length of

incisions should be more than 1:4.27

Short peripatellar incisions may

usu-ally be ignored, particularly when

they are more than a decade old

Prior transverse incisions may be

crossed with longitudinal incisions

without concern for devitalization

In the presence of multiple surgical

scars, it is preferable to use the

longest and/or most lateral incision

to avoid a large lateral skin flap that

may have a compromised vascular

supply A muscle flap or soft-tissue

expander may be needed for patients

with atrophic skin or multiple

adher-ent broad scars.25

Postoperative hemarthrosis or

hematoma formation may cause

wound problems by increasing

ten-sion If a hemarthrosis is large,

causes pain, and interferes with

range of motion or if it compromises

skin viability, early evacuation is

prudent Range-of-motion exercises

should be delayed until the wound

is stable The same is true for a large

subcutaneous hematoma, which

may compromise the viability of the

skin In morbidly obese patients,

closure of knee incisions with

reten-tion sutures may be helpful to

mini-mize subcutaneous dead space

Patient Risk Factors

Local and systemic factors known

to inhibit wound healing include

vasoconstriction due to nicotine use,

atrophy of the skin, previous

irradia-tion of tissue, and thermal or

chemi-cal burns Obesity may predispose

to wound healing problems as well;

this may be related to overzealous

retraction, fat necrosis, or residual

dead space Diabetes mellitus may

alter collagen synthesis and decrease

the tensile strength of scar tissue

Corticosteroids decrease fibroblast

proliferation, which is a necessary

component of wound healing It is

unclear whether the increased rate of deep wound infections in patients with rheumatoid arthritis is related to problematic wound healing or the prolonged use of corticosteroids

Perioperative use of drugs such as methotrexate and malnutrition may further compromise wound healing

Nutritional supplementation in pa-tients who have a serum albumin level less than 3.5 g/dL and a total lymphocyte count of less than 1,500/mm3may decrease the inci-dence of complications related to wound healing

Wound drainage beyond the first several days after surgery may in-crease the risk of infection Taking cultures of the drainage is not advis-able; these will often yield normal skin flora, and continuing prophy-lactic antibiotics longer than 24 hours is generally not necessary

Drainage will usually stop after immobilization of the limb for 24 to

48 hours; if not, the patient should undergo reoperation for explo-ration, deep culture, irrigation, and meticulous wound reclosure Knee-motion exercises may be resumed once the wound is stable If deep cultures are positive, parenteral antibiotic therapy should be contin-ued for at least 6 weeks Otherwise, antibiotics may be discontinued

Full-thickness skin necrosis must

be treated aggressively to avoid deep infection Salvage is predict-able with debridement and cover-age with a rotational gastrocnemius flap, provided the procedure is per-formed expeditiously.28 Failures may be inevitable if treatment is delayed and necrosis of the flap re-sults in contamination of the knee

Stiffness

There is a subset of patients who fail to regain the motion that one would expect in the initial postop-erative period The most important factor in predicting postoperative motion is the preoperative arc of motion

In the immediately postoperative period, limited recovery of motion

is most commonly related to post-surgical pain Patient-controlled analgesia or continuous epidural analgesia for 48 hours postopera-tively is commonly utilized to ensure adequate pain relief and allow immediate motion The effi-cacy of continuous-passive-motion machines continues to be debated

It is difficult to quantify the rate at which knee motion should im-prove, although the rate should be more rapid in the initial 2 to 4 weeks and then slower for the sub-sequent 6 weeks Paradoxically, overzealous therapy or activity may cause stiffness due to pain and in-flammation Other common causes include arthrofibrosis, low-grade infection, excessive soft-tissue ten-sion due to improper releases or overstuffing of the joint, a tight pos-terior cruciate ligament, reflex sym-pathetic dystrophy, and mechanical loosening

If motion gains are slow within the first 6 to 8 weeks, gentle manip-ulation under anesthesia may be beneficial Delaying manipulation beyond 3 months after the scar has matured will increase the risk of periprosthetic fracture or tendon rupture In these circumstances, arthrolysis, either arthroscopic or open, may be necessary Arthro-scopic arthrolysis is particularly useful when there is limited scar formation, located primarily in the infrapatellar region, the intercondy-lar notch, and the peripatelintercondy-lar re-gion When the medial and lateral gutters are scarred, open arthrolysis

is recommended Management in the initial postoperative period after arthrolysis should include continuous epidural analgesia and supervised physical therapy Occult sepsis may also predis-pose to stiffness after total knee arthroplasty Diagnosing acute infection (within 4 weeks after surgery) is often difficult, as

consti-tutional symptoms, such as fevers

and chills, are uncommon The

workup should include a complete

blood cell count with differential,

erythrocyte sedimentation rate,

C-reactive protein assay, aspiration

with culture and cell count, and

plain radiographs Nuclear

medi-cine scans are difficult to interpret

and lack accuracy in the early

post-operative period

Occasionally, despite a thorough

evaluation, no obvious cause of pain

and motion loss is identified Under

these circumstances, continued

ob-servation with time for resolution of

the synovial inflammation may be

indicated Synovial biopsy with

wound culture and frozen-section

histoanalysis may be considered.29

Mechanical factors may limit

motion and cause pain If a tight

flexion gap is present, flexion will

be limited The femoral component

may be oversized, tensing the

reti-naculum This can often be treated

by increasing slightly the posterior

tibial slope or by recessing the

pos-terior cruciate ligament in

cruciate-retaining designs A tight flexion

space may also be present when the

femoral component has a rotational

imbalance, creating a trapezoidal

flexion gap This is addressed by

recutting the femur and using a

posterolateral wedge to ensure

ade-quate external rotation of the

femoral component

If a flexion contracture is being

caused by a tight extension space, a

posterior capsular release may be

performed with assessment of

residual posterior osteophytes,

which would cause a relative

con-tracture of the posterior capsule

This problem may also be

ad-dressed by resecting an additional

portion of the distal femur A

pos-teriorly offset femoral component

or an oversized femoral component

may further decrease the flexion

space This can generally be

ad-dressed by downsizing the femoral

component in a more appropriate

position and resecting an additional portion of the posterior femoral condyle Resecting additional tibia

in this situation will be effective only if the extension space is com-parably tight Otherwise, the flexion-extension mismatch will persist In the presence of varus or valgus deformities, the medial capsular sleeve or lateral soft-tissue re-straints must be balanced appropri-ately

Limited access to physical

thera-py or an inappropriate program may play a role in the development

of stiffness It appears that physical therapy, particularly in the initial period after total knee arthroplasty,

is beneficial With the current em-phasis on shorter hospitalization, it

is critical that patients be enrolled expeditiously in supervised home physical therapy programs It must

be emphasized that lack of timely physical therapy or overzealous therapy may adversely affect mo-tion Poor patient motivation and low pain thresholds may also have

a negative impact on motion gains

Potentially affected patients must

be identified and coached through-out the postoperative period

Periprosthetic Femoral and Tibial Fractures

Advanced osteoporosis, neurologic disorders, rheumatoid arthritis, chronic corticosteroid therapy, and notching of the anterior femoral cortex may predispose the patient

to distal femur fracture after total knee arthroplasty The relationship between femoral notching and sub-sequent fracture is often debated;

however, in one study involving use of a biomechanical model, a

3-mm defect was shown to decrease the torsional strength of the distal femur by 29.2%.30 Risk factors for periprosthetic tibial fractures are less well established, but are likely quite similar

Treatment depends on the frac-ture pattern, the medical and func-tional status of the patient, the integrity of the bone-prosthesis interfaces, and the quality of bone stock Treatment options include immobilization in traction or a cast, open reduction and internal tion, indirect reduction and fixa-tion, and revision total knee arthro-plasty Orthogonal radiographs are critical to appropriately evalu-ate the fracture pattern Traction views may be helpful

Nonoperative treatment is advis-able for minimally displaced frac-tures when the alignment of the fracture and limb can be maintained

in a well-molded long-leg or spica cast In general, a cast can be used for 6 weeks, after which a switch to

a long-leg hinged brace will allow early gentle range-of-motion exer-cises The brace is worn until there

is evidence of healing of the fracture

as well as adequate quadriceps strength Results of nonoperative treatment have been unsatisfactory, with high rates of motion loss, malalignment, nonunion, and sys-temic problems associated with pro-longed immobilization

In the presence of malalignment, fracture displacement, or compro-mise of the prosthesis interfaces, surgical intervention is advisable Open reduction and internal fixa-tion may be performed with either intramedullary devices or a variety

of plate constructs (Fig 9) Inter-locked retrograde nailing may not

be possible when certain

posterior-ly stabilized femoral components are used, when a closed box con-struct is present, or when there is inadequate distal bone stock Ret-rograde nailing has the benefit of indirect reduction of the fracture without stripping the soft tissues

A large-diameter nail is preferred Locking bolts may be applied to the distal interlocking screws to augment fixation when there is marked osteoporosis An