- Email: [email protected]
Knee prostheses
Knee Prostheses By Robert
Schneider,
Amy Beth Goldman,
and John N. lnsall
HISTORY
ARLY SURGICAL ATTEMPTS at knee arthroplasty began in the mid- and late 19th century and included interposition of soft tissue structures between the damaged articular surfaces and attempts at smoothing the surfaces. Due to their limited success, these procedures were not widely accepted. Metallic molds, similar to the cup used in arthroplasty of the hip, were developed in the 1940sand were also abandoned. Increased clinical use of total knee arthroplasty began in the 1950s with the development of two different designsof prostheses.At one end of the spectrum were the constrained hinged prosthesesused by Walldius’ in 1951, Shier? in 1954, and the Guepar group3 in 1970 (Fig 1). At the opposite end were the surface replacements which only provided a smooth articular surface
E
Fig 2. Surface replacement. This ICLH prosthesis failed due to mechanical loosening. The lateral view shows a radiolucent line et the cement-bond interface around the entire tibia1 component, which has subsided into the cancellous bone end is tilted anteriorly. There is severe erosion of the articular surface of the patella.
and added no stability to the joint. Replacement of the tibia1 articular surfaces by metallic discs was reported by MacIntosh4 in 1958, and McKeever’ in 1960. The polycentric prosthesis,a design that resurfaced both the femoral and tibia1 sides of the joint and used methylmethacrylate cement to fix the components was described by Gunston in 1971. Other examples of first generation surface replacement prostheses were the duocondylar, geomedic, UCI, modular, and ICLH (Fig 2). Although the first generation of prostheses often achieved initial success,there was a rapidly increasing rate of failure over time due to mechanical loosening,
Fig 1. First garter&m total knao prostheses. Constrained prosthuis: the Guepar linked hinged prosthesis had both metallic femoral and tibia1 components. The prosthesis was fixed in the bone with radiopaque methylmethacrylate cement.
sf3min8rs in Roamgenology, Vol XXI, No 1 (January),
1986: pp 29-46
From the Departmeni of Radiology, The Hospital for Special Surgery, afiliated with New York Hospital-Cornell University Medical College, New York. Robert Schneider: Assistant Professor of Radiology, Cornell University Medical College; Amy Beth Goldman: Professor of Clinical Radiology, Cornell University Medical College; John N. Insall: Professor of Orthopedic Surgery. Cornell University Medical College. Address reprint requests to Robert Schneider, MD. Hospital for Special Surgery, 535 E 70th St, New York, NY
10021. 0 1986 by Grune & Stratton, inc.
0037-198X/86/21014005$05.00/0 29
30
Second generation total knee prosthesis. (A Fig 3. end B) This tote1 condyler prosthesis is composed of a metallic femoral component, e radiolucent polyethylene tibia1 component, and e polyethylene patellar resurfacing button, all fixed by rediopaque cement. The tibia1 component has a cup-shaped or conceve erticular surface, intercondyler eminence (long arrow) to prevent trenslocation, end en intramedullary fixation peg (short arrow). (Cl On the lateral roentgenogram, there is e thin lucent line at the cement-bone interface of the anterior flange of the femoral component.
SCHNEIDER,
GOLDMAN,
AND
INSALL
31
KNEE PROSTHESES
subsidenceof the tibia1 component, and femoropatellar pain.‘-’ The hinged models were prone to loosening, infection, and fractures of either the metal stemsor cement. The second generation of knee prostheses began in 1973 with the introduction of the total condylar prosthesis, a modification of the earlier surface replacements (Fig 3).“*” This design, along with other second generation prostheses, solved many of the problems that had caused failure of the earlier models: (1) tibia1 component loosening was addressed by the use of intramedullary fixation pegs. (2) Special instruments were developed to aid in alignment of the components. (3) The problem of patellar pain due to arthritis was solved by the use of patellar resurfacing components (4) Instability and subluxation were prevented by soft tissue realignment procedures. (5) Improved techniques of introducing methylmethacrylate cement enhanced fixation. Many of the second generation knee prostheseshave been in place for more than ten years without failure, so that the average lifespan of the more modern designs is not known. INDICATIONS
made these negative factors relatively lessimportant than in former years.‘* ALTERNATIVE
METHODS OF TREATMENT
Total knee arthroplasty is usually considered only after other methods of therapy have failed or are not considered to be appropriate.13Nonoperative treatment of articular diseaseincludes oral anti-inflammatory medications, intraarticular injections of steroids, use of a cane, and weight reduction.14Temporizing surgical procedures include debridement, synovectomy, and osteotomy. An osteotomy is most often considered in the individual under 60 years who has symptoms localized to one compartment of the joint.13 The basic principle of this procedure is to remove a wedge of bone from either above or below the joint to correct for abnormal femorotibia1 alignment and to shift the majority of the weight bearing forces onto the more normal side of the joint. In medial compartment diseasewith a moderate genu varus, the osteotomy is performed in the upper tibia. In severegenu varus or in patients with lateral compartment diseaseand
AND CONTRAINDICATIONS
Total knee replacement is indicated primarily for the relief of pain due to severedamage to the articular surfaces. Secondary indications include decreased mobility interfering with ambulation, varus or valgus deformity, and disabling instability of the joint. Degenerative arthritis, posttraumatic arthritis, osteonecrosis, noninfectious inflammatory arthritis, and burnt out infections arthritis can all produce sufficient damage to require a total joint replacement. The severity of the radiographic abnormalities does not always correlate with the severity of the symptoms. Age, subjective interference with life style by the destroyed joint, and physical examination are also important factors in determining if a total knee arthroplasty is necessary. Contraindications to total knee replacement include active infection, arthrodesis, quadriceps, weakness,and paralysis. Occasionally, a rapidly progressiveangular deformity, severeloss of subchondral bone, or lossof ligamentous support due to neuroarthropathy may make the total knee replacement technically difficult. However, newer designs and a larger selection of prostheseshave
Fig 4. Preoperative plain film evaluation. Standing AP roentgenogram shows severe narrowing of the medial joint compartment and a genu varus deformity. There is loss of cancelloos bone of the medial tibia1 plateau.
32
SCHNEIDER,
Fig 5. component
Nonconstrained and polyethylene
prosthesis. (A and BI AP and lateral views. tibia1 component. Only the medial compartment
genu valgus, a supracondylar osteotomy of the femur is indicated. Osteotomy, if successful,provides relief of pain for from five to fifteen years.” The disadvantage of osteotomy, when compared with total knee replacement, is that the rate of successis lower and it takes a longer period of time to achieve symptomatic improvement and functional rehabilitation. In young active individuals, in patients with infection that is difficult to eradicate, and in some patients with failed total joint replacements, an arthrodesis may be preferable to a prosthesis. Surgical fusion of the knee does provide a painless joint that will last the patient’s lifetime. However, arthrodesis results in limitation of motion; particularly uncomfortable is the resultant inability to flex the knee while sitting. PREOPERATIVE ROENTGENOGRAPHIC EVALUATION
Routine preoperative radiographs, at the Hospital for Special Surgery, include a standing AP view, a recumbent lateral view, and a standard skyline view of the patella.“j The AP projection is obtained during weight-bearing to allow for bet-
Unicondylar prosthesis is replaced.
GOLDMAN,
with
AND
a metallic
INSALL
femoral
ter assessment of joint space narrowing and femorotibial alignment that can be obtained with the patient supine (Fig 4). Some institutions advocate that the standing AP view be filmed on a long cassettein order to visualize the hip, knee, and ankle on the same radiograph for better evaluation of alignment. All three projections are useful in planning the bone cuts that are necessary to correct preoperative deformities. Radionuclide bone scans may be of value in cases in which the decision between osteotomy and total joint replacement is not clear cut.” Augmented uptake of the bone-seeking radionuelide in both the medial and lateral compartments mitigates against an osteotomy, which relies on one side of the joint being preserved. CLASSIFICATION
AND BASIC DESIGNS
Various classifications of knee prosthesis have been proposed but a standard classification has not yet been widely accepted.133’8 In reference to the descriptions of total knee replacements, the term constraint refers to the stability imparted to the knee by the prosthesis.
KNEE PROSTHESES
33
Fig 6. Semiconstrained kinematic posterior cruciate retention prosthesis. (A. B, and C) There is a metallic femoral component and polyethylene tibia1 and patellar components with metal backing. Although there is a notch in the tibiil component for retention of the postarior cruciete ligament. it is not visible roentgenographicalIY.
Today, over 90% of the knee prostheses inserted are of either nonconstrained or semiconstrained design. Nonconstrained prostheses merely replace the articular surfaces and rely on intact collateral and cruciate ligaments for stability. They usually have a relatively flat tibia1 articular surface. There are unicondylar models that replace just the medial or lateral compartments, but these are infrequently used (Fig 5). i9,” Semiconstrained prosthesesprovide some stability to the knee by the design of the compo-
nents, with the useof a cup-shapedconcavetibia1 surface (Figs 3, 6, and 7). Subluxation is prevented by selecting a tibia1 plateau that is thick enough to keep the collateral ligaments taut after releasing the contracted collateral ligament on the concave side of the angular deformity. In some semiconstrained prostheses, the anterior and posterior cruciate ligaments are sacrificed, as in the total condylar prosthesis (Fig 3), while in other designs, a notch is present in the tibia1 component for retention of the posterior cruciate
Fi g 7. Semiconstrained Posterior stabilized condylar prosthesis. There is a metallic femoral component with an inter condylar bar. (A) AP view. The metal backed polyethylene tibia1 component has a tibia1 peg (arrow) projecting upwa rds bar to prevent posterior subluxation of the tibia. (8) A patellar resurfacing button is present. that abuts the intercondylar
Semiconstrained prosthesis in a patient with loss of bone stock. (A) The preoperative AP roentgenogrem shows Fig 8. severe osteoarthritis of the medial joint compartment with erosion end loss of cencellous bone of the medial tibia1 plateau end a severe genu varus deformity. (8) The postoperative AP roentgenogrem reveals a total condyler prosthesis. Bone graft transfixed with two screws fills the bony defect in the medial tibia1 plateau. The genu varus deformity has been corrected.
35
ligament, as in the kinematic type (Fig 6).21 There are also models of semiconstrained prostheses that substitute for an absent or sacrificed posterior cruciate ligament, as in the posterior stabilized condylar prosthesis (Fig 7).22 Constrained prosthesesprovide stability in all directions. There are both linked and nonlinked designs. The linked constrained prostheses have femoral and tibia1 components that are connected, often by a hinge that allows flexion and extension but not axial rotation (Fig 1). In the normal knee, the tibia rotates externally on the femur during extension and internally during flexion. The failure of the hinged design to permit a rotational motion increases the potential for mechanical loosening. Another drawback to the hinged prosthesis is that metal on metal articulation produces more wear particles than metal on polyethylene. In addition, the resection of the large amount of bone necessaryto implant a hinged prosthesis makes revision technically difficult. Hinged prosthesesnow are used mainly for limb salvage in bone tumors. There are newer linked and nonlinked constrained prosthesesthat do permit axial rotation. Constrained prostheses are primarily reserved for patients with severe ligamentous compromise, and those with severe loss of bone stock from diseaseor the removal of a previous prosthesis.
metallic tray or the polyethylene molded over a metallic skeleton (Figs 6 and 7). The patellar resurfacing component is also composedof high density polyethylene, sometimes with metal backing (Figs 3 and 6). Methylmethacrylate cement, containing barium to make it radiopaque, is now used for fixation of most knee prostheses.At someinstitutions, fixation by bone ingrowth into a porous-coated prosthesis is being used instead of cement. Sufficient data on this new technique so far are unavailable to determine its efficacy. As was stated previously, some semiconstrained prostheses sacrifice the anterior and posterior cruciate ligaments, while others preserve the posterior cruciate ligament in a groove on the tibia1 component. When the posterior cruciate ligament is absent, there may be a
POSTOPERATIVE ROENTGENOGRAPHIC EVALUATION
The majority of prostheses being used today are of the semiconstrained type from the total condylar series (Figs 3 and 7) and the kinematic series (Fig 6). The remainder of this article will deal primarily with this design, its evaluation, and its complications. The most commonly used semiconstrained designs have a metallic femoral component made of cobalt-chrome alloy and a tibia1 component made of high density polyethylene (Figs 3,6, and 7). The plastic plateaus are radiolucent, slightly concave, and fit tightly against the metal femoral condyles with no soft tissue space between the surfaces. One or more pegs extend downward from the plastic articular surface into the tibia1 metaphysis to aid in fixing this component. In the early designs (Fig 3), the tibia1 component was entirely radiolucent. In more recent models, the polyethylene tibia1 component may be placed in a
Introoperative Fig 9. genogram obtained in the in the mediil cortex of the on the femoral component
cortical fracture. An AP roentrecovery room shows a fracture diil femur just above the stem (arrow).
SCHNEIDER,
GOLDMAN,
Fig 10. Infectious loosening. (A) AP roentgenogram shows a wide radiolucent line at the cement-bone medial and lateral aspects of the tibia1 plateau. (B) The lateral view shows soft tissue swelling and a wide cement-bone interface of the patellar resurfacing.
greater tendency for posterior subluxation of the tibia with respect to the femur. There are designs, such as the posterior stabilized condylar prosthesis (Fig 7), which compensate for an absent posterior cruciate ligament by providing a central peg that projects upward from the tibia1 component and abuts a transverse intercondylar bar on the femoral component when excessive posterior displacement of the tibia occurs (Fig 7). Preoperative loss of bone substance in the plateaus may be compensated for in several ways: extra cement reinforced with metallic screwsor mesh, bone graft below the cement (Fig 8), or custom-designed components with extra support on the deficient side. Radiographic evaluation of the total knee replacement begins with a supine AP view obtained in the recovery room. This immediate
AND
INSALL
interface of the lucent line at the
postoperative study is used to exclude any gross malalignment of components and fractures that occurred during placement of the prosthesis (Fig 9). As soonas the patient is able to bear weight, a complete knee series, including a standing AP view, a recumbent lateral view and a skyline view of the patella, is obtained. This study functions as the baseline for comparison with subsequent studies. Repeat films are taken six months following surgery and then, if no problems intervene, at yearly intervals. When evaluating serial roentgen studies, important roentgen criteria include (1) a progressive decrease in soft tissue swelling, (2) integrity of the metal, cement, and bone, (3) femorotibial alignment (4Oto 7“ of valgus on the AP study, the metallic femoral condyles in the concavity of the lucent plastic plateaus on the lateral study), (4) alignment of the components
KNEE PROSTHESES
37
relative to the femur and tibia, and (5) no increase in the width or extent of the lucent lines at the cement-bone interfaces after the first year. As in total hip prostheses, thin lucent lines (measuring less than 2 mm) may occur in total knee replacements for a variety of reasons, such as movement of the prosthesis before the cement is fixed, interposition of blood or fibrous tissue between the bone and cement, and bone resorp tion due to reaction to the cement or mechanical stress.23-25Serial postoperative films greatly facilitate evaluation of these lucent lines. These lucencies usually appear within the first year and most frequently occur at the periphery of the medial and lateral plateaus.” Constrained prostheses have a higher incidence of lucent lines than non- or semiconstrained designs.” In all types of total knee replacements, evaluation of the cement-bone interfaces is more complex than in total hip replacements. In the knee, subtle changes in the width of the lucent lines at the cement-bone interfaces may be mimicked by flexion or rotation or may vary with centering of the film.“S25A radiolucency at the cement-bone interface around the femoral component is even more difficult to assess than one around the periphery of the tibia1 plateaus. This is because of the curved shape of the condyles and because the cement-bone interface of the femoral component is only visible on the lateral view.
Fii 11. Acute Section. An arthrogram formed in a patient with an infected total prosthesl shows contrast material extending posterior abscess cavity.
perknee into a
The University of Pennsylvania has established a scoring system based on the optimum placement of the prosthesis. Their technical criteria include 3O to 7O of knee valgus, a tibia1 plateau that is perfectly horizontal in both AP and lateral planes, the femoral component in 4O to 7“ of valgus, and both components centered at the midline of the joint.26 Failure to meet these technical ideals correlates statistically with postoperative complications, although not all cases with an imperfectly placed prosthesis become symptomatic. 26 The suggested ideal alignment and position may vary somewhat with the different models. COMPLICATIONS
General Concepts
The successful total knee arthroplasty results in a joint that is free of pain, stable, and capable of at least 90° of flexion.*’ The majority of postoperative complications present with pain, soft tissue swelling, and either limited motion or at the opposite end of the spectrum, a feeling of “giving way” accompanied by ligamentous laxity* Unlike the hip prosthesis, which has a ball and socket configuration with intrinsic mechanical stability, most knee prosthesesdepend heavily on adjacent soft tissue support. Thus, additional problems related to the unique anatomy of the
Fig 12. Mechanical loosening of tibia1 component in three different patients. (A) This patient shows a wide radiolucency at the cement-bona interface of the tibia1 component. This line extends not only below the plateaus but around the fixation peg. (6) Tilting of the tibia1 component with subsidence of the medial side of the plateau and lifting of the lateral side of the plateau off the bone. A wide radiolucency is present at the cament-bone interface of the entire tibia1 component including the peg. (12) Severe varus deformity with plastic deformation of the tibia1 component. The peg is in normal position; however, both the prosthetic and osseous medial tibia1 plateaus have sunk downward.
KNEE PROSTHESES
knee joint occur, such as patellar complications and cruciate deficient joints. In order of frequency, the complications that require revision of a total knee replacement are infection, mechanical loosening, ligamentous instability, and secondary fracture that damages the prosthetic fixation.” Other factors that affect the clinical outcome but may or may not necessitate a secondsurgical procedure, include femoropatellar pain (from arthritis, fracture, dislocation, or separation of the resurfacing material), stress fracture, and soft tissue abnormality (contracture, myositis ossificans). Infection Deep infection is the most serious complication of total knee arthroplasty.27*29The septic joint may appear early, within three months of surgery, or late after 3 months, and up to years after the operation. Regardless of the time interval, bacteremia, resulting from dental surgery,
39
manipulation of the urinary tract, or distant infection, may result in seeding of the tissues around the prosthesis. Deep infections may present clinically as either acute or chronic problems. The incidence of infection complicating semiconstrained type of total knee prosthesis varies, but averages ~2%. 29Predilection for secondary infection is increased with the constrained hinged prosthesis, and in patients with rheumatoid arthritis regardless of the design of the joint replacement. The roentgen criteria suggesting infectious loosening of a total knee replacement include a wide lucent line (>2 mm) at either the cementbone or cement-metal interface of one or more of the components; rapid increase in width of the lucent line when compared with a prior study; and periosteal new bone formation (Fig 10). Although far from specific, widened or poorly marginated lucent lines without a thin sclerotic
Fig 13. Mechanioal loosening of femoral component. (A) Lateral roentgenogram of a poaerior stebilized condylar prostheaia in Feb lM3 shows good alignment without abnormal radiilucency at the cement-bone interface. (6) Repeat study in July 1984 demonstrates fragmentation of bone and cement anteriorly and shii in position of the femoral component. There are wide lucent lines along both the cement-bone and cement-metal interfaces at the anterior femoral component.
40
SCHNEIDER,
GOLDMAN,
AND INSALL
the fact that these patients presented with severe pain, and revision surgery was carried out on the basis of the clinical signs before roentgen changes had occurred. However, even in chronic cases, only four of nine cases had plain film findings of infectious loosening. Therefore, absenceof roentgen signs doesnot exclude infection complicating a total knee arthroplasty. The role of radionuclide bone scanning in the identification of the complications of total knee prostheses is controversial. Advocated by some investigators as a useful screening study, the results are qualitative, so that abnormal uptake must be graded as mild, moderate, or severe.3oIts utility is further limited by the observation that the usual postoperative augmented uptake may be present for over a year, rendering the examination useless in early infection. However, a negative bone scan virtually excludes the presence of infection.
Fig 14. Arthrographic study for evaluation of a painful prosthesis. (A) This porous coated anatomic (PCA) prosthesis has been fixed with radiopaque cement. The contrast material is diicult to distinguish from the cement and the metal. (6) Subtraction film shows the contrast material as black against the white metal and cement. There is slight extension of contrast material into the cement-bone interface around the tibia1 plateau (arrows) but not around the two fixation pegs. The prosthesis was not loose at revision surgery.
rim at the junction with the normal bone favor infectious as opposed to mechanical loosening (Fig 10). Schneider et al?* reviewing 20 cases of infected prosthesis, found that in 73% of the acute casesthe plain films were either negative or showed isolated soft tissue swelling. The low incidence of positive roentgenograms was due to
Fig 15. Varus instability. About four years after a total condylar prosthesis an abnormal space (arrow) has appeared between the lateral femoral condyle and lateral tibia1 plateau, indicating a varus deformity.
41
Arthrography is performed primarily to confirm that the needle is within the pseudocapsule of the prosthesis during the aspiration. A positive culture establishes the diagnosis of infection, but a negative one does not exclude it. Operative cultures, particularly from the cement-bone interface, may be more reliable. Rarely, the contrast study may demonstrate an abscesscavity (Fig 11). The arthrogram may also be useful in determining if a sinus tract communicates with the prostheses. Mechanical loosening is another causeof painful prosthesis. Preoperative factors that predispose to early loosening, if not corrected during the placement of the knee arthroplasty, include femorotibial malalignment or subluxation, and varus or valgus deformity indicating ligamentous instability or bone loss at the tibia1 plateau (Fig 4).27 Preoperative varus is particularly emphasized in biomechanical studies becauseit leads to asymmetric overload of the medial plateau with
compressive failure of the underlying cancellous bone and subsequentloosening of the tibia1 component.3’ Immediate postoperative films can also identify findings that correlate with premature mechanical loosening. Most are related to technical difficulties in placement of the prosthesis, such as malaligned components within the bones, abnormal femorotibial alignment associatedwith excessivevarus or valgus angulation at the knee joint, poor cement fixation, and failure to compensate for a deficient medial plateau.1’*26~28.32 Mechanical loosening of a total knee prosthesis most frequently occurs in the tibia1 component.27’28 The most widely recognized stigmata of loosening of the components of total joint replacement is an abnormal lucent line at the cement-bone or cement-metal interfaces. More significant than isolated widening of a lucent line at the cement-bone interface of the tibia1 component is widening that is accompanied by progressive extension of the line around the tibia1 peg (Fig 12).“*28
Fig 16. Vslgus instebility. An early postoperative film showed normal aliinment with 7” of genu velgus. This late film demonstrates velgus instabilii with increase in genu valgus to 20” and a space between the medial femoral condyle end medial tibia1 plateau.
Fig 17. Anterior instability. Leteral roentgenogram shows anterior displacement of the tibia with respect to the femur. The metal condyles extend behind the plastic plateaus and are no longer centered in the concavity of the tibia1 component.
Mechanical Loosening
SCHNEIDER,
42
GOLDMAN,
AND
INSALL
the anterior flange (Fig 3C).” With a grossly loosened femoral component, the radiographs reveal wide lucent lines at the cement-bone or cement-metal interfaces or alteration in the position of the components relative to the osseous femur (Fig 13). Roentgen signs of mechanical loosening may be present in asymptomatic individuals. Presumably the loosening, identified on serial roentgen studies, may precede the clinical signs. The role of arthrography in the diagnosis of loosening of the components of total knee replacement has been limited, in our experience. Subtraction technique is useful since the methylmethacrylate cement, which surrounds the prosthesis, is impregnated with barium and has a density close to that of the contrast material (Renografin 60%). Extension of the iodinated material into the cement-bone interface around the tibia1 peg is reliable evidence of loosening. Less striking finds are equivocal (Fig 14).
Stress fracture (arrows) in a patient Fig 18. total condylar replacement for rheumatoid arthritis.
with
a
The diagnosis of mechanical loosening of the tibia1 component is facilitated by the presenceof abnormalities other than interface lucencies. Shift of position, most frequently tilting of the tibia1 component into varus position, is indicative of failure of fixation. It is often accompanied by sinking or subsidence of component into the medial metaphysis.27V28 Other roentgen criteria of loosening of the tibia1 component include collapse of the underlying cancellous bone, fragmentation of the cement, and plastic deformation of the tibia1 component itself (Fig 12).1’*2~2892 Less commonly, collapse of the tibia1 component occurs in the posterior, anterior (Fig 2), or lateral portions of the component rather than the medial plateau. Diagnosis of early mechanical loosening femoral component is difficult. Even a minor degree of rotation may alter the roentgen appearance of the interface.2’*27In a well-fixed component, a thin lucency can, in some cases,be visible along
Ligumentous Instability In the widely used semiconstrained prosthesis preoperative varus or valgus deformities are corrected by releasing the ligaments on the concave side and placing a tibia1 component of sufficient size to act as a spacer between the osseous articular surfaces.“*27 Postoperative ligamentous instability may result in varus, valgus, anterior, posterior,
Fig 18. Metal fatigue Guepar hinged prosthesis.
fracture
in the femoral
stem of a
43
KNEE PROSTHESES
Fig 20. Patellar fractures in two different patients. (A) Nondisplaced transverse fracture view reveals a complex fracture of the patella and displacement of bony fragments.
medial, lateral, or rotatory malalignment. On the standing AP projection, varus or valgus instability will appear as an abnormal angular deformity centered at the joint with a soft tissue space between the plastic plateau and the metal condyle on the convex side (Figs 15 and 16). The varus deformity is the more common of the two and may result from lateral ligamentous laxity, loosening of the tibia1 component, collapse of the cancellous bone of the tibia1 plateau, or all three. The abnormal separation between the plastic lateral tibia1 plateau and the metal condyle establishesthe presenceof a soft tissue deficiency at least contributing to the varus angulation (Fig 15).
through
the patella.
(B) Skyline
Routine or stress lateral views may demonstrate the presenceof anterior or posterior instability of the prosthesis. In anterior instability, the condyles extend behind the lip of the concave plastic plateaus (Fig 17). Fractures
Osseousfracture may complicate the clinical course of any prosthesis. Predisposing factors include severejuxtaarticular osteoporosis,a prosthetic model that requires the removal of a large amount of bone, such as the Guepar, technical problems during surgery that result in a breach of the cortex (Fig 9), and a mechanical loosening of a component.
44
SCHNEIDER,
GOLDMAN,
AND
INSALL
Osseous fracture complicating a total knee replacement may either be the result of stressor of trauma. In caseswith total condylar or similar prostheses,supracondylar fractures are the most common and may involve the cement as well as the bone. These fractures may or may not require revisional surgery. Stress fracture in the shaft of an adjacent bone, although a cause of pain, is unlikely to result in a poor postsurgical result (Fig 18). An isotopic bone scan may be used to differentiate an insufficiency injury in the adjacent bone from a primary problem with the prosthesis. Stress fracture of the bony tibia1 plateau or femoral condyle beneath the prosthesis may result in loosening.33 Metal fatigue fracture is primarily a problem of the constrained hinged prosthesis with an intramedullary stem (Fig 19). Loosening and displacement Fig 22. surfacing from the patella.
of the pateilar
re-
Patellar Complications Femoropatellar pain following total joint replacement is a clinical problem specific to the
Heterotopic bone formation. (A) One month after surgery, a poorly defined density has appeared Fig 23. anterior to the distal femoral shift. (6) Nine months later, mature heterotopic bone is attached to the anterior femur.
in the tissues cortex of the
45
KNEE PROSTHESES
knee, occurring in 4% of cases.34In prosthetic designs that replace only the femoral and tibia1 articular surfaces, femoropatellar pain can be due to unaddressedpreexisting arthritic changes or postoperative cartilage erosion resulting from contact with the metal condyles (Fig 2). Resurfacing of the patellar has gained wide acceptance.The patellar button has obviated the problem of cartilage loss and decreasedthe incidence of postoperative femoropatellar pain. However, it has resulted in its own set of complications. Fracture of the patella may occur postoperatively and result in quadriceps weakness.” Technical factors that predispose to patellar injury include inadequate lateral ligamentous release to insure proper tracking, failure to test tracking after the tourniquets are released,interference with the blood supply while preparing the patellar bed, and inadequate bone stock.34 Postoperative patellar fracture may be transverse or involve only the upper or lower pole (Fig 20). Injuries associated with distraction of the fragments result in an extension lag, while nondisplaced breaks causeonly localized pain.”
It is infrequent that a patellar fracture will lead to revision of the prosthesis. Dislocation or subluxation of the patella also occurs. The displacement may involve both the osseouspatella and the prosthetic resurfacing, (Fig 21) or the resurfacing may remain within the intercondylar notch while the bone becomesdisplaced. Other complications associated with patellar resurfacing include loosening of the button (Fig 22) and avulsion of the patellar tendon.“,34 Myositis Ossificans
Heterotopic ossification is frequently seen following a total knee replacement. It is usually of little or no clinical significance. The major problem is recognizing that the presence of myositis ossificans, particularly when it is immature, is a postsurgical change and does not indicate the presence of infection (Fig 23). Three common sites of heterotopic ossification associated with total knee replacement are adjacent to the anterior femoral shaft, within the quadriceps tendon, and parallel to the medial plateau.
REFERENCES 1. Walldius B: Arthroplasty of the knee joint using an endoprosthesis. Acra Orthop Sand 1957;24(suppl) 2. Shiers L: Arthroplasty of the knee. Preliminary report of a new method. J Bone Joint Surg 1954;36-B:553-560 3. Witvoet J, Guepar Group: Guepar total knee prosthesis. The Knee Joint: Proceedings of International Congress, Rotterdam, The Netherlands 1973. Exerpta Med 1974;298:305-3 15 4. Macintosh D: Hemiarthroplasty of the knee using a space occupying prosthesis for painful varus and valgus deformities. J Bone Joint Surg 1958;40-A:1431 (abstr) 5. McKeever DC: Tibia1 plateau prosthesis. C/in Orthop 1960;18:86-95 6. Gunston F: Polycentric knee arthroplasty. Prosthetic simulation of normal knee movement. J Bone Joint Surg 197 1;53-B:272-277 7. Cracchiolo A III, Benson M, Finerman GA, et al: A prospective comparative clinical analysis of the first-generation knee replacements: Polycentric vs. geometric knee arthroplasty. Clin Orthop 1979;145:37-46 8. Insall JN, Ranawat CS, Aglietti P, et al: A comparison of four models of total knee replacement. J Bone Joint Surg 1976;58-A:754-765 9. Waugh MTW: Estimating the survival time of knee replacements. J Bone Joint Surg 1982;64-B:579-582 10. Insall JN, Scott WN, Ranawat CS: The total condylar knee prosthesis. A report of two hundred cases. J Bone Joint Surg 1979;61-A:173-180 11. Insall JN, Hood RW, Flawn LB, et al: The total condylar knee prosthesis in gonarthrosis. A five to nine year
follow-up of the first one hundred consecutive replacements.
J Bone Joint Surg 1983;65-A:619-628 12. Insall JN: Total knee replacement. In: lnsall JN (ed): Surgery of the Knee. New York: Churchill Livingstone, 1984;587-695 13. Insall JN, Binazzi R, Soudry M, et al: Total knee arthroplasty. Clin Orthop 1984;192:13-22 14. Landon GC, Galante JO, Casini J: Essay on total knee arthroplasty. Clin Orthop 1984;192:69-74 15. Waugh TR: Total knee arthroplasty in 1984. Clin Orthop 1984;192:4&45 16. Merchant A, Mercer R, Jacobsen R, et al: Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg 1974;56-A:1391-1396 17. Thomas RH, Resnick D, Alazraki MP: Compartmental evaluation of osteoarthritis of the knee. Radiology 1975;116:585-594 18. Laskin RS: The spectrum of total knee replacement. In: Laskin RS, Denham RA, Apley AG (eds): Replacement of Knee. Berlin: Springer-Verlag. 1984;l t-45 19. Insall JN, Aglietti, P: A five to seven year follow-up of unicondylar arthroplasty. J Bone Joint Surg 1980,62A:1329-1337 20. Marmor L: Marmor modular knee in unicompartmental disease. J Bone Joint Surg 1979;61-A:347-353 21. Ewald FC, Jacobs MA, Miegel RE, et al: Kinematic total knee replacement. J Bone Joint Surg 1984;66-A:10321039 22. lnsall JN, Lachiewicz PF, Burstein AH: The posterior
46 stabilized condylar prosthesis: A modification of the total condylar design. J Bone Joint Surg 1982;64-A:1317-l 323 23. Ahlberg A, Linden B: The radiolucent zone in arthroplasty of the knee. Acta Orthop Stand 1977;48:687-690 24. Reckling FW, Asher MA, Dillon WL: A longitudinal study of the radiolucent line at the bone-cement interface following total joint-replacement procedures. J Bone Joint Surg 1977;59-A:355358 25. Tibrewal SB, Grant KA, Goodfellow JW: The radiolucent line beneath the tibia1 components of the Oxford meniscal knee. J Bone Joint Surg 1984;66-B:523-528 26. Lotke PA, Ecker ML: Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg 1977;59-A:77-79 27. Cameron HU, Hunter GA: Failure in total knee arthroplasty. Chin Orthop 1982;170:141-146 28. Schneider R, Abenavoli AM, Soudry M, et al: Failure of total condylar knee replacement. Radiology 1984; 152:309-315
SCHNEIDER,
GOLDMAN,
AND
INSALL
29. Habermann ET: Revision arthroplasty for failed total knee replacement. In: Hungerford DS, Krackow KA, Kenna RV (eds): Total Knee Arthroplasty. A Comprehensive Approach. Baltimore: Williams & Wilkins, 1984;219-257 30. Hunter JC, Hattner RS, Murray WR, et al: Loosening of the total knee arthroplasty: detection by radionuclide bonescanning. AJR 1980;135:131-136 3 1. Ducheyne P, Kagan A III, Lacey JA: Failure of total knee arthroplasty due to loosening and deformation of the tibia1 component. J Bone Joint Surg 1978;60-A:384-391 32. Bartel DL, Burstein AH, Santavicca EA, et al: Performance of the tibia1 component in total knee replacement. J Bone Joint Surg 1982;64-A:1026-1033 33. Rand JA, Coventry MB: Stress fractures after total knee arthroplasty. JBone Joint Surg 1980;62-A:226233 34. Clayton ML, Thirupathi R: Patellar complications after total condylar arthroplasty. Clin Orthop 1982;170:152155
Schneider,
Amy Beth Goldman,
and John N. lnsall
HISTORY
ARLY SURGICAL ATTEMPTS at knee arthroplasty began in the mid- and late 19th century and included interposition of soft tissue structures between the damaged articular surfaces and attempts at smoothing the surfaces. Due to their limited success, these procedures were not widely accepted. Metallic molds, similar to the cup used in arthroplasty of the hip, were developed in the 1940sand were also abandoned. Increased clinical use of total knee arthroplasty began in the 1950s with the development of two different designsof prostheses.At one end of the spectrum were the constrained hinged prosthesesused by Walldius’ in 1951, Shier? in 1954, and the Guepar group3 in 1970 (Fig 1). At the opposite end were the surface replacements which only provided a smooth articular surface
E
Fig 2. Surface replacement. This ICLH prosthesis failed due to mechanical loosening. The lateral view shows a radiolucent line et the cement-bond interface around the entire tibia1 component, which has subsided into the cancellous bone end is tilted anteriorly. There is severe erosion of the articular surface of the patella.
and added no stability to the joint. Replacement of the tibia1 articular surfaces by metallic discs was reported by MacIntosh4 in 1958, and McKeever’ in 1960. The polycentric prosthesis,a design that resurfaced both the femoral and tibia1 sides of the joint and used methylmethacrylate cement to fix the components was described by Gunston in 1971. Other examples of first generation surface replacement prostheses were the duocondylar, geomedic, UCI, modular, and ICLH (Fig 2). Although the first generation of prostheses often achieved initial success,there was a rapidly increasing rate of failure over time due to mechanical loosening,
Fig 1. First garter&m total knao prostheses. Constrained prosthuis: the Guepar linked hinged prosthesis had both metallic femoral and tibia1 components. The prosthesis was fixed in the bone with radiopaque methylmethacrylate cement.
sf3min8rs in Roamgenology, Vol XXI, No 1 (January),
1986: pp 29-46
From the Departmeni of Radiology, The Hospital for Special Surgery, afiliated with New York Hospital-Cornell University Medical College, New York. Robert Schneider: Assistant Professor of Radiology, Cornell University Medical College; Amy Beth Goldman: Professor of Clinical Radiology, Cornell University Medical College; John N. Insall: Professor of Orthopedic Surgery. Cornell University Medical College. Address reprint requests to Robert Schneider, MD. Hospital for Special Surgery, 535 E 70th St, New York, NY
10021. 0 1986 by Grune & Stratton, inc.
0037-198X/86/21014005$05.00/0 29
30
Second generation total knee prosthesis. (A Fig 3. end B) This tote1 condyler prosthesis is composed of a metallic femoral component, e radiolucent polyethylene tibia1 component, and e polyethylene patellar resurfacing button, all fixed by rediopaque cement. The tibia1 component has a cup-shaped or conceve erticular surface, intercondyler eminence (long arrow) to prevent trenslocation, end en intramedullary fixation peg (short arrow). (Cl On the lateral roentgenogram, there is e thin lucent line at the cement-bone interface of the anterior flange of the femoral component.
SCHNEIDER,
GOLDMAN,
AND
INSALL
31
KNEE PROSTHESES
subsidenceof the tibia1 component, and femoropatellar pain.‘-’ The hinged models were prone to loosening, infection, and fractures of either the metal stemsor cement. The second generation of knee prostheses began in 1973 with the introduction of the total condylar prosthesis, a modification of the earlier surface replacements (Fig 3).“*” This design, along with other second generation prostheses, solved many of the problems that had caused failure of the earlier models: (1) tibia1 component loosening was addressed by the use of intramedullary fixation pegs. (2) Special instruments were developed to aid in alignment of the components. (3) The problem of patellar pain due to arthritis was solved by the use of patellar resurfacing components (4) Instability and subluxation were prevented by soft tissue realignment procedures. (5) Improved techniques of introducing methylmethacrylate cement enhanced fixation. Many of the second generation knee prostheseshave been in place for more than ten years without failure, so that the average lifespan of the more modern designs is not known. INDICATIONS
made these negative factors relatively lessimportant than in former years.‘* ALTERNATIVE
METHODS OF TREATMENT
Total knee arthroplasty is usually considered only after other methods of therapy have failed or are not considered to be appropriate.13Nonoperative treatment of articular diseaseincludes oral anti-inflammatory medications, intraarticular injections of steroids, use of a cane, and weight reduction.14Temporizing surgical procedures include debridement, synovectomy, and osteotomy. An osteotomy is most often considered in the individual under 60 years who has symptoms localized to one compartment of the joint.13 The basic principle of this procedure is to remove a wedge of bone from either above or below the joint to correct for abnormal femorotibia1 alignment and to shift the majority of the weight bearing forces onto the more normal side of the joint. In medial compartment diseasewith a moderate genu varus, the osteotomy is performed in the upper tibia. In severegenu varus or in patients with lateral compartment diseaseand
AND CONTRAINDICATIONS
Total knee replacement is indicated primarily for the relief of pain due to severedamage to the articular surfaces. Secondary indications include decreased mobility interfering with ambulation, varus or valgus deformity, and disabling instability of the joint. Degenerative arthritis, posttraumatic arthritis, osteonecrosis, noninfectious inflammatory arthritis, and burnt out infections arthritis can all produce sufficient damage to require a total joint replacement. The severity of the radiographic abnormalities does not always correlate with the severity of the symptoms. Age, subjective interference with life style by the destroyed joint, and physical examination are also important factors in determining if a total knee arthroplasty is necessary. Contraindications to total knee replacement include active infection, arthrodesis, quadriceps, weakness,and paralysis. Occasionally, a rapidly progressiveangular deformity, severeloss of subchondral bone, or lossof ligamentous support due to neuroarthropathy may make the total knee replacement technically difficult. However, newer designs and a larger selection of prostheseshave
Fig 4. Preoperative plain film evaluation. Standing AP roentgenogram shows severe narrowing of the medial joint compartment and a genu varus deformity. There is loss of cancelloos bone of the medial tibia1 plateau.
32
SCHNEIDER,
Fig 5. component
Nonconstrained and polyethylene
prosthesis. (A and BI AP and lateral views. tibia1 component. Only the medial compartment
genu valgus, a supracondylar osteotomy of the femur is indicated. Osteotomy, if successful,provides relief of pain for from five to fifteen years.” The disadvantage of osteotomy, when compared with total knee replacement, is that the rate of successis lower and it takes a longer period of time to achieve symptomatic improvement and functional rehabilitation. In young active individuals, in patients with infection that is difficult to eradicate, and in some patients with failed total joint replacements, an arthrodesis may be preferable to a prosthesis. Surgical fusion of the knee does provide a painless joint that will last the patient’s lifetime. However, arthrodesis results in limitation of motion; particularly uncomfortable is the resultant inability to flex the knee while sitting. PREOPERATIVE ROENTGENOGRAPHIC EVALUATION
Routine preoperative radiographs, at the Hospital for Special Surgery, include a standing AP view, a recumbent lateral view, and a standard skyline view of the patella.“j The AP projection is obtained during weight-bearing to allow for bet-
Unicondylar prosthesis is replaced.
GOLDMAN,
with
AND
a metallic
INSALL
femoral
ter assessment of joint space narrowing and femorotibial alignment that can be obtained with the patient supine (Fig 4). Some institutions advocate that the standing AP view be filmed on a long cassettein order to visualize the hip, knee, and ankle on the same radiograph for better evaluation of alignment. All three projections are useful in planning the bone cuts that are necessary to correct preoperative deformities. Radionuclide bone scans may be of value in cases in which the decision between osteotomy and total joint replacement is not clear cut.” Augmented uptake of the bone-seeking radionuelide in both the medial and lateral compartments mitigates against an osteotomy, which relies on one side of the joint being preserved. CLASSIFICATION
AND BASIC DESIGNS
Various classifications of knee prosthesis have been proposed but a standard classification has not yet been widely accepted.133’8 In reference to the descriptions of total knee replacements, the term constraint refers to the stability imparted to the knee by the prosthesis.
KNEE PROSTHESES
33
Fig 6. Semiconstrained kinematic posterior cruciate retention prosthesis. (A. B, and C) There is a metallic femoral component and polyethylene tibia1 and patellar components with metal backing. Although there is a notch in the tibiil component for retention of the postarior cruciete ligament. it is not visible roentgenographicalIY.
Today, over 90% of the knee prostheses inserted are of either nonconstrained or semiconstrained design. Nonconstrained prostheses merely replace the articular surfaces and rely on intact collateral and cruciate ligaments for stability. They usually have a relatively flat tibia1 articular surface. There are unicondylar models that replace just the medial or lateral compartments, but these are infrequently used (Fig 5). i9,” Semiconstrained prosthesesprovide some stability to the knee by the design of the compo-
nents, with the useof a cup-shapedconcavetibia1 surface (Figs 3, 6, and 7). Subluxation is prevented by selecting a tibia1 plateau that is thick enough to keep the collateral ligaments taut after releasing the contracted collateral ligament on the concave side of the angular deformity. In some semiconstrained prostheses, the anterior and posterior cruciate ligaments are sacrificed, as in the total condylar prosthesis (Fig 3), while in other designs, a notch is present in the tibia1 component for retention of the posterior cruciate
Fi g 7. Semiconstrained Posterior stabilized condylar prosthesis. There is a metallic femoral component with an inter condylar bar. (A) AP view. The metal backed polyethylene tibia1 component has a tibia1 peg (arrow) projecting upwa rds bar to prevent posterior subluxation of the tibia. (8) A patellar resurfacing button is present. that abuts the intercondylar
Semiconstrained prosthesis in a patient with loss of bone stock. (A) The preoperative AP roentgenogrem shows Fig 8. severe osteoarthritis of the medial joint compartment with erosion end loss of cencellous bone of the medial tibia1 plateau end a severe genu varus deformity. (8) The postoperative AP roentgenogrem reveals a total condyler prosthesis. Bone graft transfixed with two screws fills the bony defect in the medial tibia1 plateau. The genu varus deformity has been corrected.
35
ligament, as in the kinematic type (Fig 6).21 There are also models of semiconstrained prostheses that substitute for an absent or sacrificed posterior cruciate ligament, as in the posterior stabilized condylar prosthesis (Fig 7).22 Constrained prosthesesprovide stability in all directions. There are both linked and nonlinked designs. The linked constrained prostheses have femoral and tibia1 components that are connected, often by a hinge that allows flexion and extension but not axial rotation (Fig 1). In the normal knee, the tibia rotates externally on the femur during extension and internally during flexion. The failure of the hinged design to permit a rotational motion increases the potential for mechanical loosening. Another drawback to the hinged prosthesis is that metal on metal articulation produces more wear particles than metal on polyethylene. In addition, the resection of the large amount of bone necessaryto implant a hinged prosthesis makes revision technically difficult. Hinged prosthesesnow are used mainly for limb salvage in bone tumors. There are newer linked and nonlinked constrained prosthesesthat do permit axial rotation. Constrained prostheses are primarily reserved for patients with severe ligamentous compromise, and those with severe loss of bone stock from diseaseor the removal of a previous prosthesis.
metallic tray or the polyethylene molded over a metallic skeleton (Figs 6 and 7). The patellar resurfacing component is also composedof high density polyethylene, sometimes with metal backing (Figs 3 and 6). Methylmethacrylate cement, containing barium to make it radiopaque, is now used for fixation of most knee prostheses.At someinstitutions, fixation by bone ingrowth into a porous-coated prosthesis is being used instead of cement. Sufficient data on this new technique so far are unavailable to determine its efficacy. As was stated previously, some semiconstrained prostheses sacrifice the anterior and posterior cruciate ligaments, while others preserve the posterior cruciate ligament in a groove on the tibia1 component. When the posterior cruciate ligament is absent, there may be a
POSTOPERATIVE ROENTGENOGRAPHIC EVALUATION
The majority of prostheses being used today are of the semiconstrained type from the total condylar series (Figs 3 and 7) and the kinematic series (Fig 6). The remainder of this article will deal primarily with this design, its evaluation, and its complications. The most commonly used semiconstrained designs have a metallic femoral component made of cobalt-chrome alloy and a tibia1 component made of high density polyethylene (Figs 3,6, and 7). The plastic plateaus are radiolucent, slightly concave, and fit tightly against the metal femoral condyles with no soft tissue space between the surfaces. One or more pegs extend downward from the plastic articular surface into the tibia1 metaphysis to aid in fixing this component. In the early designs (Fig 3), the tibia1 component was entirely radiolucent. In more recent models, the polyethylene tibia1 component may be placed in a
Introoperative Fig 9. genogram obtained in the in the mediil cortex of the on the femoral component
cortical fracture. An AP roentrecovery room shows a fracture diil femur just above the stem (arrow).
SCHNEIDER,
GOLDMAN,
Fig 10. Infectious loosening. (A) AP roentgenogram shows a wide radiolucent line at the cement-bone medial and lateral aspects of the tibia1 plateau. (B) The lateral view shows soft tissue swelling and a wide cement-bone interface of the patellar resurfacing.
greater tendency for posterior subluxation of the tibia with respect to the femur. There are designs, such as the posterior stabilized condylar prosthesis (Fig 7), which compensate for an absent posterior cruciate ligament by providing a central peg that projects upward from the tibia1 component and abuts a transverse intercondylar bar on the femoral component when excessive posterior displacement of the tibia occurs (Fig 7). Preoperative loss of bone substance in the plateaus may be compensated for in several ways: extra cement reinforced with metallic screwsor mesh, bone graft below the cement (Fig 8), or custom-designed components with extra support on the deficient side. Radiographic evaluation of the total knee replacement begins with a supine AP view obtained in the recovery room. This immediate
AND
INSALL
interface of the lucent line at the
postoperative study is used to exclude any gross malalignment of components and fractures that occurred during placement of the prosthesis (Fig 9). As soonas the patient is able to bear weight, a complete knee series, including a standing AP view, a recumbent lateral view and a skyline view of the patella, is obtained. This study functions as the baseline for comparison with subsequent studies. Repeat films are taken six months following surgery and then, if no problems intervene, at yearly intervals. When evaluating serial roentgen studies, important roentgen criteria include (1) a progressive decrease in soft tissue swelling, (2) integrity of the metal, cement, and bone, (3) femorotibial alignment (4Oto 7“ of valgus on the AP study, the metallic femoral condyles in the concavity of the lucent plastic plateaus on the lateral study), (4) alignment of the components
KNEE PROSTHESES
37
relative to the femur and tibia, and (5) no increase in the width or extent of the lucent lines at the cement-bone interfaces after the first year. As in total hip prostheses, thin lucent lines (measuring less than 2 mm) may occur in total knee replacements for a variety of reasons, such as movement of the prosthesis before the cement is fixed, interposition of blood or fibrous tissue between the bone and cement, and bone resorp tion due to reaction to the cement or mechanical stress.23-25Serial postoperative films greatly facilitate evaluation of these lucent lines. These lucencies usually appear within the first year and most frequently occur at the periphery of the medial and lateral plateaus.” Constrained prostheses have a higher incidence of lucent lines than non- or semiconstrained designs.” In all types of total knee replacements, evaluation of the cement-bone interfaces is more complex than in total hip replacements. In the knee, subtle changes in the width of the lucent lines at the cement-bone interfaces may be mimicked by flexion or rotation or may vary with centering of the film.“S25A radiolucency at the cement-bone interface around the femoral component is even more difficult to assess than one around the periphery of the tibia1 plateaus. This is because of the curved shape of the condyles and because the cement-bone interface of the femoral component is only visible on the lateral view.
Fii 11. Acute Section. An arthrogram formed in a patient with an infected total prosthesl shows contrast material extending posterior abscess cavity.
perknee into a
The University of Pennsylvania has established a scoring system based on the optimum placement of the prosthesis. Their technical criteria include 3O to 7O of knee valgus, a tibia1 plateau that is perfectly horizontal in both AP and lateral planes, the femoral component in 4O to 7“ of valgus, and both components centered at the midline of the joint.26 Failure to meet these technical ideals correlates statistically with postoperative complications, although not all cases with an imperfectly placed prosthesis become symptomatic. 26 The suggested ideal alignment and position may vary somewhat with the different models. COMPLICATIONS
General Concepts
The successful total knee arthroplasty results in a joint that is free of pain, stable, and capable of at least 90° of flexion.*’ The majority of postoperative complications present with pain, soft tissue swelling, and either limited motion or at the opposite end of the spectrum, a feeling of “giving way” accompanied by ligamentous laxity* Unlike the hip prosthesis, which has a ball and socket configuration with intrinsic mechanical stability, most knee prosthesesdepend heavily on adjacent soft tissue support. Thus, additional problems related to the unique anatomy of the
Fig 12. Mechanical loosening of tibia1 component in three different patients. (A) This patient shows a wide radiolucency at the cement-bona interface of the tibia1 component. This line extends not only below the plateaus but around the fixation peg. (6) Tilting of the tibia1 component with subsidence of the medial side of the plateau and lifting of the lateral side of the plateau off the bone. A wide radiolucency is present at the cament-bone interface of the entire tibia1 component including the peg. (12) Severe varus deformity with plastic deformation of the tibia1 component. The peg is in normal position; however, both the prosthetic and osseous medial tibia1 plateaus have sunk downward.
KNEE PROSTHESES
knee joint occur, such as patellar complications and cruciate deficient joints. In order of frequency, the complications that require revision of a total knee replacement are infection, mechanical loosening, ligamentous instability, and secondary fracture that damages the prosthetic fixation.” Other factors that affect the clinical outcome but may or may not necessitate a secondsurgical procedure, include femoropatellar pain (from arthritis, fracture, dislocation, or separation of the resurfacing material), stress fracture, and soft tissue abnormality (contracture, myositis ossificans). Infection Deep infection is the most serious complication of total knee arthroplasty.27*29The septic joint may appear early, within three months of surgery, or late after 3 months, and up to years after the operation. Regardless of the time interval, bacteremia, resulting from dental surgery,
39
manipulation of the urinary tract, or distant infection, may result in seeding of the tissues around the prosthesis. Deep infections may present clinically as either acute or chronic problems. The incidence of infection complicating semiconstrained type of total knee prosthesis varies, but averages ~2%. 29Predilection for secondary infection is increased with the constrained hinged prosthesis, and in patients with rheumatoid arthritis regardless of the design of the joint replacement. The roentgen criteria suggesting infectious loosening of a total knee replacement include a wide lucent line (>2 mm) at either the cementbone or cement-metal interface of one or more of the components; rapid increase in width of the lucent line when compared with a prior study; and periosteal new bone formation (Fig 10). Although far from specific, widened or poorly marginated lucent lines without a thin sclerotic
Fig 13. Mechanioal loosening of femoral component. (A) Lateral roentgenogram of a poaerior stebilized condylar prostheaia in Feb lM3 shows good alignment without abnormal radiilucency at the cement-bone interface. (6) Repeat study in July 1984 demonstrates fragmentation of bone and cement anteriorly and shii in position of the femoral component. There are wide lucent lines along both the cement-bone and cement-metal interfaces at the anterior femoral component.
40
SCHNEIDER,
GOLDMAN,
AND INSALL
the fact that these patients presented with severe pain, and revision surgery was carried out on the basis of the clinical signs before roentgen changes had occurred. However, even in chronic cases, only four of nine cases had plain film findings of infectious loosening. Therefore, absenceof roentgen signs doesnot exclude infection complicating a total knee arthroplasty. The role of radionuclide bone scanning in the identification of the complications of total knee prostheses is controversial. Advocated by some investigators as a useful screening study, the results are qualitative, so that abnormal uptake must be graded as mild, moderate, or severe.3oIts utility is further limited by the observation that the usual postoperative augmented uptake may be present for over a year, rendering the examination useless in early infection. However, a negative bone scan virtually excludes the presence of infection.
Fig 14. Arthrographic study for evaluation of a painful prosthesis. (A) This porous coated anatomic (PCA) prosthesis has been fixed with radiopaque cement. The contrast material is diicult to distinguish from the cement and the metal. (6) Subtraction film shows the contrast material as black against the white metal and cement. There is slight extension of contrast material into the cement-bone interface around the tibia1 plateau (arrows) but not around the two fixation pegs. The prosthesis was not loose at revision surgery.
rim at the junction with the normal bone favor infectious as opposed to mechanical loosening (Fig 10). Schneider et al?* reviewing 20 cases of infected prosthesis, found that in 73% of the acute casesthe plain films were either negative or showed isolated soft tissue swelling. The low incidence of positive roentgenograms was due to
Fig 15. Varus instability. About four years after a total condylar prosthesis an abnormal space (arrow) has appeared between the lateral femoral condyle and lateral tibia1 plateau, indicating a varus deformity.
41
Arthrography is performed primarily to confirm that the needle is within the pseudocapsule of the prosthesis during the aspiration. A positive culture establishes the diagnosis of infection, but a negative one does not exclude it. Operative cultures, particularly from the cement-bone interface, may be more reliable. Rarely, the contrast study may demonstrate an abscesscavity (Fig 11). The arthrogram may also be useful in determining if a sinus tract communicates with the prostheses. Mechanical loosening is another causeof painful prosthesis. Preoperative factors that predispose to early loosening, if not corrected during the placement of the knee arthroplasty, include femorotibial malalignment or subluxation, and varus or valgus deformity indicating ligamentous instability or bone loss at the tibia1 plateau (Fig 4).27 Preoperative varus is particularly emphasized in biomechanical studies becauseit leads to asymmetric overload of the medial plateau with
compressive failure of the underlying cancellous bone and subsequentloosening of the tibia1 component.3’ Immediate postoperative films can also identify findings that correlate with premature mechanical loosening. Most are related to technical difficulties in placement of the prosthesis, such as malaligned components within the bones, abnormal femorotibial alignment associatedwith excessivevarus or valgus angulation at the knee joint, poor cement fixation, and failure to compensate for a deficient medial plateau.1’*26~28.32 Mechanical loosening of a total knee prosthesis most frequently occurs in the tibia1 component.27’28 The most widely recognized stigmata of loosening of the components of total joint replacement is an abnormal lucent line at the cement-bone or cement-metal interfaces. More significant than isolated widening of a lucent line at the cement-bone interface of the tibia1 component is widening that is accompanied by progressive extension of the line around the tibia1 peg (Fig 12).“*28
Fig 16. Vslgus instebility. An early postoperative film showed normal aliinment with 7” of genu velgus. This late film demonstrates velgus instabilii with increase in genu valgus to 20” and a space between the medial femoral condyle end medial tibia1 plateau.
Fig 17. Anterior instability. Leteral roentgenogram shows anterior displacement of the tibia with respect to the femur. The metal condyles extend behind the plastic plateaus and are no longer centered in the concavity of the tibia1 component.
Mechanical Loosening
SCHNEIDER,
42
GOLDMAN,
AND
INSALL
the anterior flange (Fig 3C).” With a grossly loosened femoral component, the radiographs reveal wide lucent lines at the cement-bone or cement-metal interfaces or alteration in the position of the components relative to the osseous femur (Fig 13). Roentgen signs of mechanical loosening may be present in asymptomatic individuals. Presumably the loosening, identified on serial roentgen studies, may precede the clinical signs. The role of arthrography in the diagnosis of loosening of the components of total knee replacement has been limited, in our experience. Subtraction technique is useful since the methylmethacrylate cement, which surrounds the prosthesis, is impregnated with barium and has a density close to that of the contrast material (Renografin 60%). Extension of the iodinated material into the cement-bone interface around the tibia1 peg is reliable evidence of loosening. Less striking finds are equivocal (Fig 14).
Stress fracture (arrows) in a patient Fig 18. total condylar replacement for rheumatoid arthritis.
with
a
The diagnosis of mechanical loosening of the tibia1 component is facilitated by the presenceof abnormalities other than interface lucencies. Shift of position, most frequently tilting of the tibia1 component into varus position, is indicative of failure of fixation. It is often accompanied by sinking or subsidence of component into the medial metaphysis.27V28 Other roentgen criteria of loosening of the tibia1 component include collapse of the underlying cancellous bone, fragmentation of the cement, and plastic deformation of the tibia1 component itself (Fig 12).1’*2~2892 Less commonly, collapse of the tibia1 component occurs in the posterior, anterior (Fig 2), or lateral portions of the component rather than the medial plateau. Diagnosis of early mechanical loosening femoral component is difficult. Even a minor degree of rotation may alter the roentgen appearance of the interface.2’*27In a well-fixed component, a thin lucency can, in some cases,be visible along
Ligumentous Instability In the widely used semiconstrained prosthesis preoperative varus or valgus deformities are corrected by releasing the ligaments on the concave side and placing a tibia1 component of sufficient size to act as a spacer between the osseous articular surfaces.“*27 Postoperative ligamentous instability may result in varus, valgus, anterior, posterior,
Fig 18. Metal fatigue Guepar hinged prosthesis.
fracture
in the femoral
stem of a
43
KNEE PROSTHESES
Fig 20. Patellar fractures in two different patients. (A) Nondisplaced transverse fracture view reveals a complex fracture of the patella and displacement of bony fragments.
medial, lateral, or rotatory malalignment. On the standing AP projection, varus or valgus instability will appear as an abnormal angular deformity centered at the joint with a soft tissue space between the plastic plateau and the metal condyle on the convex side (Figs 15 and 16). The varus deformity is the more common of the two and may result from lateral ligamentous laxity, loosening of the tibia1 component, collapse of the cancellous bone of the tibia1 plateau, or all three. The abnormal separation between the plastic lateral tibia1 plateau and the metal condyle establishesthe presenceof a soft tissue deficiency at least contributing to the varus angulation (Fig 15).
through
the patella.
(B) Skyline
Routine or stress lateral views may demonstrate the presenceof anterior or posterior instability of the prosthesis. In anterior instability, the condyles extend behind the lip of the concave plastic plateaus (Fig 17). Fractures
Osseousfracture may complicate the clinical course of any prosthesis. Predisposing factors include severejuxtaarticular osteoporosis,a prosthetic model that requires the removal of a large amount of bone, such as the Guepar, technical problems during surgery that result in a breach of the cortex (Fig 9), and a mechanical loosening of a component.
44
SCHNEIDER,
GOLDMAN,
AND
INSALL
Osseous fracture complicating a total knee replacement may either be the result of stressor of trauma. In caseswith total condylar or similar prostheses,supracondylar fractures are the most common and may involve the cement as well as the bone. These fractures may or may not require revisional surgery. Stress fracture in the shaft of an adjacent bone, although a cause of pain, is unlikely to result in a poor postsurgical result (Fig 18). An isotopic bone scan may be used to differentiate an insufficiency injury in the adjacent bone from a primary problem with the prosthesis. Stress fracture of the bony tibia1 plateau or femoral condyle beneath the prosthesis may result in loosening.33 Metal fatigue fracture is primarily a problem of the constrained hinged prosthesis with an intramedullary stem (Fig 19). Loosening and displacement Fig 22. surfacing from the patella.
of the pateilar
re-
Patellar Complications Femoropatellar pain following total joint replacement is a clinical problem specific to the
Heterotopic bone formation. (A) One month after surgery, a poorly defined density has appeared Fig 23. anterior to the distal femoral shift. (6) Nine months later, mature heterotopic bone is attached to the anterior femur.
in the tissues cortex of the
45
KNEE PROSTHESES
knee, occurring in 4% of cases.34In prosthetic designs that replace only the femoral and tibia1 articular surfaces, femoropatellar pain can be due to unaddressedpreexisting arthritic changes or postoperative cartilage erosion resulting from contact with the metal condyles (Fig 2). Resurfacing of the patellar has gained wide acceptance.The patellar button has obviated the problem of cartilage loss and decreasedthe incidence of postoperative femoropatellar pain. However, it has resulted in its own set of complications. Fracture of the patella may occur postoperatively and result in quadriceps weakness.” Technical factors that predispose to patellar injury include inadequate lateral ligamentous release to insure proper tracking, failure to test tracking after the tourniquets are released,interference with the blood supply while preparing the patellar bed, and inadequate bone stock.34 Postoperative patellar fracture may be transverse or involve only the upper or lower pole (Fig 20). Injuries associated with distraction of the fragments result in an extension lag, while nondisplaced breaks causeonly localized pain.”
It is infrequent that a patellar fracture will lead to revision of the prosthesis. Dislocation or subluxation of the patella also occurs. The displacement may involve both the osseouspatella and the prosthetic resurfacing, (Fig 21) or the resurfacing may remain within the intercondylar notch while the bone becomesdisplaced. Other complications associated with patellar resurfacing include loosening of the button (Fig 22) and avulsion of the patellar tendon.“,34 Myositis Ossificans
Heterotopic ossification is frequently seen following a total knee replacement. It is usually of little or no clinical significance. The major problem is recognizing that the presence of myositis ossificans, particularly when it is immature, is a postsurgical change and does not indicate the presence of infection (Fig 23). Three common sites of heterotopic ossification associated with total knee replacement are adjacent to the anterior femoral shaft, within the quadriceps tendon, and parallel to the medial plateau.
REFERENCES 1. Walldius B: Arthroplasty of the knee joint using an endoprosthesis. Acra Orthop Sand 1957;24(suppl) 2. Shiers L: Arthroplasty of the knee. Preliminary report of a new method. J Bone Joint Surg 1954;36-B:553-560 3. Witvoet J, Guepar Group: Guepar total knee prosthesis. The Knee Joint: Proceedings of International Congress, Rotterdam, The Netherlands 1973. Exerpta Med 1974;298:305-3 15 4. Macintosh D: Hemiarthroplasty of the knee using a space occupying prosthesis for painful varus and valgus deformities. J Bone Joint Surg 1958;40-A:1431 (abstr) 5. McKeever DC: Tibia1 plateau prosthesis. C/in Orthop 1960;18:86-95 6. Gunston F: Polycentric knee arthroplasty. Prosthetic simulation of normal knee movement. J Bone Joint Surg 197 1;53-B:272-277 7. Cracchiolo A III, Benson M, Finerman GA, et al: A prospective comparative clinical analysis of the first-generation knee replacements: Polycentric vs. geometric knee arthroplasty. Clin Orthop 1979;145:37-46 8. Insall JN, Ranawat CS, Aglietti P, et al: A comparison of four models of total knee replacement. J Bone Joint Surg 1976;58-A:754-765 9. Waugh MTW: Estimating the survival time of knee replacements. J Bone Joint Surg 1982;64-B:579-582 10. Insall JN, Scott WN, Ranawat CS: The total condylar knee prosthesis. A report of two hundred cases. J Bone Joint Surg 1979;61-A:173-180 11. Insall JN, Hood RW, Flawn LB, et al: The total condylar knee prosthesis in gonarthrosis. A five to nine year
follow-up of the first one hundred consecutive replacements.
J Bone Joint Surg 1983;65-A:619-628 12. Insall JN: Total knee replacement. In: lnsall JN (ed): Surgery of the Knee. New York: Churchill Livingstone, 1984;587-695 13. Insall JN, Binazzi R, Soudry M, et al: Total knee arthroplasty. Clin Orthop 1984;192:13-22 14. Landon GC, Galante JO, Casini J: Essay on total knee arthroplasty. Clin Orthop 1984;192:69-74 15. Waugh TR: Total knee arthroplasty in 1984. Clin Orthop 1984;192:4&45 16. Merchant A, Mercer R, Jacobsen R, et al: Roentgenographic analysis of patellofemoral congruence. J Bone Joint Surg 1974;56-A:1391-1396 17. Thomas RH, Resnick D, Alazraki MP: Compartmental evaluation of osteoarthritis of the knee. Radiology 1975;116:585-594 18. Laskin RS: The spectrum of total knee replacement. In: Laskin RS, Denham RA, Apley AG (eds): Replacement of Knee. Berlin: Springer-Verlag. 1984;l t-45 19. Insall JN, Aglietti, P: A five to seven year follow-up of unicondylar arthroplasty. J Bone Joint Surg 1980,62A:1329-1337 20. Marmor L: Marmor modular knee in unicompartmental disease. J Bone Joint Surg 1979;61-A:347-353 21. Ewald FC, Jacobs MA, Miegel RE, et al: Kinematic total knee replacement. J Bone Joint Surg 1984;66-A:10321039 22. lnsall JN, Lachiewicz PF, Burstein AH: The posterior
46 stabilized condylar prosthesis: A modification of the total condylar design. J Bone Joint Surg 1982;64-A:1317-l 323 23. Ahlberg A, Linden B: The radiolucent zone in arthroplasty of the knee. Acta Orthop Stand 1977;48:687-690 24. Reckling FW, Asher MA, Dillon WL: A longitudinal study of the radiolucent line at the bone-cement interface following total joint-replacement procedures. J Bone Joint Surg 1977;59-A:355358 25. Tibrewal SB, Grant KA, Goodfellow JW: The radiolucent line beneath the tibia1 components of the Oxford meniscal knee. J Bone Joint Surg 1984;66-B:523-528 26. Lotke PA, Ecker ML: Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg 1977;59-A:77-79 27. Cameron HU, Hunter GA: Failure in total knee arthroplasty. Chin Orthop 1982;170:141-146 28. Schneider R, Abenavoli AM, Soudry M, et al: Failure of total condylar knee replacement. Radiology 1984; 152:309-315
SCHNEIDER,
GOLDMAN,
AND
INSALL
29. Habermann ET: Revision arthroplasty for failed total knee replacement. In: Hungerford DS, Krackow KA, Kenna RV (eds): Total Knee Arthroplasty. A Comprehensive Approach. Baltimore: Williams & Wilkins, 1984;219-257 30. Hunter JC, Hattner RS, Murray WR, et al: Loosening of the total knee arthroplasty: detection by radionuclide bonescanning. AJR 1980;135:131-136 3 1. Ducheyne P, Kagan A III, Lacey JA: Failure of total knee arthroplasty due to loosening and deformation of the tibia1 component. J Bone Joint Surg 1978;60-A:384-391 32. Bartel DL, Burstein AH, Santavicca EA, et al: Performance of the tibia1 component in total knee replacement. J Bone Joint Surg 1982;64-A:1026-1033 33. Rand JA, Coventry MB: Stress fractures after total knee arthroplasty. JBone Joint Surg 1980;62-A:226233 34. Clayton ML, Thirupathi R: Patellar complications after total condylar arthroplasty. Clin Orthop 1982;170:152155