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The Journal of Bone and Joint Surgery (American). 2006;88:1849-1860. doi:10.2106/JBJS.E.01394 © 2006 The Journal of Bone and Joint Surgery, Inc.
Patellofemoral Arthritis
1 Mount Sinai Medical School, 5 East 98th Street, Box 1188, New York, NY 10029.
E-mail address for R.P. Grelsamer:
RGrelsamer{at}aol.com
The authors did not receive grants or outside funding in support of their
research for or preparation of this manuscript. They did not receive payments
or other benefits or a commitment or agreement to provide such benefits from a
commercial entity. No commercial entity paid or directed, or agreed to pay or
direct, any benefits to any research fund, foundation, educational
institution, or other charitable or nonprofit organization with which the
authors are affiliated or associated.
The surgeon must determine whether patellofemoral arthritis is the primary source of a patient's knee pain and whether the arthritis is truly unicompartmental. An anteromedial osteotomy of the tibial tuberosity is most effective when the arthritis is localized to the distallateral portion of the patellofemoral compartment. It is least effective when there is global arthritis of the patellofemoral articulation. Total knee arthroplasty is an effective treatment for patellofemoral arthritis. Patellofemoral replacement can be considered for selected patients. A major reason for poor results after patellofemoral replacement and patellectomy procedures is the development of femorotibial arthritis.
Unicompartmental arthritis is traditionally thought of as a condition affecting the femorotibial compartments, but it can also be isolated to the patellofemoral articulation. In fact, isolated patellofemoral arthritis may not be so rare1-3. In a radiographic study of patients over the age of forty years who had painful knees, Davies et al.2 noted that the prevalence of isolated patellofemoral arthritis was 9% (nineteen of 206 knees). McAlindon et al.4 performed a radiographic study of 273 symptomatic knees in patients over the age of fifty-five years and found a prevalence of isolated patellofemoral arthritis of 8% in women. The condition also exists, albeit at a lower frequency, in young and middle-aged people. When encountering a patient with isolated patellofemoral arthritis for whom a nonoperative approach and perhaps an arthroscopic débridement have failed, the orthopaedic surgeon can choose from a number of operations, including total knee arthroplasty and tibial tuberosity transfers as well as lateral retinacular releases, patellofemoral replacements, autologous chondrocyte implantation, facetectomy, removal of the patellar subchondral bone, and denervation. Although a total knee replacement can address any and all arthritic conditions about the knee, the surgeon may consider this to be an overly aggressive approach in the setting of unicompartmental arthritis. This would be particularly true in a young, active patient, for whom the surgeon would want the most bone-sparing procedure, and in an older, more frail patient, for whom the surgeon would want to minimize surgical dissection, operating time, and blood loss. The surgeon therefore can choose between a relatively extreme procedure with predictable results (total knee replacement) and operations demanding less surgical dissection and resection but offering less certainty. In this review, we will summarize the current thinking regarding these various options.
As is true of all articular cartilage, the articular cartilage of the patella consists of a solid phase, made up mostly of collagen and glycosaminoglycans, and a fluid phase. The solid phase is slightly permeable, and, when a load is applied to the articular surface, the fluid slowly redistributes itself within the solid matrix5,6. The pressure within the fluid is largely responsible for the cushioning effect of the articular cartilage as well as the low friction coefficient exhibited by the cartilaginous surfaces. Disruption of the articular surface by cracks, fissures, crevices, and the like leads to a loss of pressure within the fluid phase. High stresses are then borne by the collagen fibers, which become more prone to breakdown7. The ability of collagen to withstand high stresses has a variable genetic component8, which accounts for the wide range of clinical responses to a given joint load among different patients. For the purposes of this review, the term arthritis refers to full-thickness loss of articular cartilage and concomitant inflammation. Wear and damage of articular cartilage can have a biological or mechanical cause. Biological causes include inflammatory diseases and infection, although neither leads to isolated patellofemoral arthritis. Mechanical causes include all conditions associated with loads that overwhelm the capacity of cartilage to withstand them. These conditions include any combination of obesity, repetitive deep knee flexion, malalignment9,10, dysplasia, and blunt trauma. The prevalence of osteoarthritis of the knee is higher in obese individuals, presumably as a result of increased loads placed on all parts of the joint11. One part or another of the patellar cartilage remains loaded throughout the entire flexion-extension cycle, with the exception of the earliest degrees of flexion12. The distal portion of the patella is loaded as the knee flexes, and the contact area on the patella migrates proximally with progressive flexion. At 90°, the contact area is located proximally, after which the contact area moves back toward the central aspect of the patella. Thus, the central portion of the patella is the part that is most frequently loaded. It also happens to be the part of the patella that exhibits the thickest cartilage (5 mm)—in fact, the thickest cartilage in the human body12. Most activities involving knee flexion take place in a closed-kinetic-chain mode whereby the foot is on the ground. These activities include bending down, rising from a chair, and ascending stairs. Activities involving repeated bending against resistance (with body weight being the most common resistance) also lead to stresses across the patellofemoral joint. In a closed-chain mode, the forces across the patellofemoral joint increase as the knee flexes from 0° to 90°, as do the contact pressures (force per unit area)13. An improper fit between two mating surfaces leads to an abnormal stress distribution. Rotational malalignment in the axial plane9 (posterior tilt of the lateral border of the patella) results in abnormally high lateral stresses14-17 that can lead to arthritis18. A dysplastic trochlea, whereby the trochlea is flat or even convex, can also lead to unusually high loads and the development of arthritis in younger patients.
Pain is the primary symptom that should be addressed, and the surgeon must first correctly identify the source of this pain. This can be particularly challenging with the patellofemoral joint, as a large number of conditions can refer pain to the anterior aspect of the knee. These conditions include overuse, abnormal patellar tilt, plicae, neuromas, tendinitis, synovitis, and focal lesions within the patella. In addition, pain can be referred from elsewhere in the knee or from distant sites such as the hip or spine. It is tempting to attribute pain to physical changes that are clearly visible on a radiograph, on a magnetic resonance imaging scan, or to the naked eye; however, the major source of a patient's pain may in fact be abnormal intraosseous pressures, abnormal levels of biochemical mediators such as proinflammatory cytokines or substance P19, or other factors that are not readily apparent. The enhanced ability of modern imaging modalities to visualize the articular surface of the patellofemoral joint has not improved the surgeon's ability to treat patellofemoral pain20. This was well stated by Insall when he noted "Curiously, neither the wide-spread use of arthroscopy nor the advent of new diagnostic tests such as CT scanning and magnetic resonance imaging have cast much light" on the enigma of patellofemoral pain21,22. A patient with isolated patellofemoral arthritis typically describes anterior knee pain when rising from a seated position and/or ascending stairs23. The pain is diminished when the subject walks on level ground. Pain at rest should arouse suspicion of nerve-related pain, such as a neuroma, reflex sympathetic dystrophy/complex regional pain syndrome, or a radiculopathy. More rarely, pain at rest can be associated with a patellar tumor, an infection, or a stress fracture.
On the physical examination, the surgeon should observe the patient in the standing and walking position and look for a squinting (inward-pointing) patella (Fig. 1), foot pronation, and other signs of distant, pain-producing pathological conditions. With the patient seated or supine, the hips should be evaluated for signs of tightness, synovitis, and joint inflammation, since pathological conditions of the hip can present as anterior knee pain. When assessing the knee, the examiner should begin with light palpation of the soft tissues to detect a neuroma or tendinitis. This is particularly important because no current imaging study predictably reveals these conditions. If they are not diagnosed at the time of the physical examination, they may be missed completely. The presence or absence of patellar tilt needs to be determined on the physical examination10, since many imaging reports fail to make note of it. A key sign of symptomatic patellofemoral arthritis on the physical examination is tenderness of the lateral (or occasionally medial) facet of the patella10. The examiner assesses this by gently curling the fingers under the lateral (or medial) border of the patella. In the setting of clinically meaningful patellofemoral arthritis, this causes pain. (In applying pressure to the facet, the examiner is simultaneously applying pressure to all of the soft tissues between the skin and bone, including the retinaculum and the synovium. The specific source of the pain can therefore be debated.) The critical imaging study is the Merchant radiograph, for which the patient is placed supine on the imaging table with the knees angled over the end of the table and supported by a variable angle device24 (Fig. 2). It is imperative that there not be overlap between the patella and the underlying trochlea, so that apparent approximation of the two structures represents true joint-space narrowing rather than a radiographic artifact. Although the original article by Merchant et al. described a knee flexion angle of 45°24, lesser angles, such as 30°, are more desirable as they allow imaging of a more proximal portion of the patellofemoral joint. Since trochlear dysplasias are most commonly proximal, it is imperative that this portion of the compartment be visualized. Although one may choose magnetic resonance imaging or computerized tomography over a well-made Merchant radiograph, these are not cost-effective methods for arriving at the same conclusions.
Having judged that the patellofemoral compartment is an important source of pain, one must determine whether the arthritis is truly isolated to this compartment. The absence of joint line tenderness is insufficient evidence that femorotibial arthritis is absent, and one must not fail to order a complete set of radiographs. These include not only standing anteroposterior, true lateral25, and Merchant radiographs, but also the standing tunnel view, also known as the Rosenberg view26,27 or the schuss view because of the crude resemblance to a schussing skier23 (Fig. 3). When made adequately, the standing tunnel view is indistinguishable from a supine tunnel view, inasmuch as there is no overlap between the femur and tibia and the notch is clearly visible. It is a critical projection because often it alone reveals arthritis that is localized to the central and posterior aspects of the femorotibial compartments (Figs. 4-A and 4-B).
Magnetic resonance imaging and arthroscopy can also be useful for evaluating the femorotibial compartments, as can a nuclear bone scan, the only imaging modality that provides a measure of a compartment's metabolic activity. A controversial issue is the extent to which nonarthritic chondral changes (e.g., partial-thickness defects) can be present in other compartments before the patellofemoral arthritis can no longer be considered isolated. Corpe and Engh28 investigated a similar issue in their evaluation of isolated unicompartmental arthritis of the femorotibial articulation. In a study of patients who had undergone femorotibial unicompartmental knee replacement, they noted that scattered non-full-thickness chondral changes in the untreated compartments did not affect the results. It is not known whether these findings can be extrapolated to the patellofemoral joint. Patellofemoral arthritis can be a subtle reflection of otherwise subclinical inflammatory arthritis. Serum analysis for inflammatory conditions such as rheumatoid arthritis is warranted, and in the United States an infectious workup for Lyme disease should also be considered29.
Few outcome instruments were designed specifically for the assessment of the patellofemoral joint30, and none has been uniformly accepted by surgeons experienced in the treatment of patellofemoral disease. The development of such an instrument is difficult because of the potentially different expectations for the function of this joint among patients in different age groups. Therefore, an outcome instrument that targets older patients with arthritis, such as the popular Western Ontario and McMaster Universities Osteoarthritis (WOMAC) instrument, may be overly favorable to patients with patellofemoral arthritis, who are generally younger, while an instrument that measures sports activity and instability, such as the Lysholm instrument, may be overly unfavorable to such patients. The Knee Society Score (KSS) Clinical Rating System has been used with some frequency for evaluating patients with knee replacements, but it cannot be self-administered and its reliability and validity have been questioned31,32. The International Knee Documentation Committee (IKDC)33 instrument has shown good validity and reliability in the evaluation of patellofemoral disorders, but it has not been assessed in the context of arthritis31,34. The Short Form-36 (SF-36) has been validated for evaluation of quality of life34,35, but it requires computerized analysis, which limits its clinical accessibility31.
The Knee Injury and Osteoarthritis Outcome Score (KOOS)36 (www.koos.nu) is a forty-two-question tool consisting of the reliable WOMAC instrument with the addition of items pertaining to younger, active patients. It has the advantage of being self-administered, with patients able to complete it in approximately ten minutes. Paxton and Fithian recommended its use in the setting of patellofemoral arthritis31, but it has not yet been utilized with any degree of frequency.
Initially, most patients with patellofemoral arthritis can be treated with a nonoperative approach. This includes activity modification, medications, weight control, physical therapy, and possibly bracing, nutritional supplements, and viscosupplementation. Activity modification involves an avoidance of squats, wall-slides, and large steps as well as the admonition that, during exercise, pain should not be "worked through" but avoided altogether. Medications include anti-inflammatory drugs and analgesics, in isolation or in combination. The challenge of physical therapy is to strengthen and stretch the structures about the knee without eliciting pain. Water exercises can be beneficial in that regard. A knee support used in the setting of patellofemoral arthritis should feature an anterior cutout to minimize direct pressure on the patellofemoral joint. Nutritional supplements have not been conclusively found to be helpful in the treatment of arthritis, but substances such as glucosamine appear to be safe37,38. Preliminary studies suggest that viscosupplementation is potentially beneficial39,40.
Lateral Retinacular Release A lateral retinacular release should shift the patellofemoral contact area medially. The operation can therefore be expected to be more successful in patients in whom the medial articular cartilage is intact, but this has not been studied, to our knowledge. It is also not known how far medial the displacement must be for the operation to be successful. The procedure incidentally denervates the patella to a certain extent, and it is unknown to what degree that contributes to the success of the operation when it works. Aderinto and Cobb41 reviewed the results at an average of thirty-one months (range, twelve to sixty-five months) after lateral retinacular release in fifty-three patients with patellofemoral arthritis (with or without concomitant femorotibial arthritis). Four patients required a knee replacement within eighteen months. Of the remaining forty-nine patients, twenty-six had isolated patellofemoral arthritis. Thirteen of those twenty-six patients were very satisfied or satisfied with the result of the lateral release, whereas the other thirteen were dissatisfied. Unfortunately, the authors did not differentiate between patients with lateral arthritis and those with global (patellar and trochlear) involvement.
Total Knee Replacement In a study of fifty-three patients who had been followed for an average of 7.4 years after total knee replacement with resurfacing of the patella to treat isolated patellofemoral arthritis, Laskin and van Steijn44 noted an average range of motion of 122°, compared with 117° in a separate cohort of patients with tricompartmental disease, with 81% (forty-three) of the fifty-three patients having a good-to-excellent result. Parvizi et al.45 evaluated the results of thirty-one knee replacements in twenty-four patients at an average of five years. They noted that twenty-one patients required a lateral retinacular release and three more required a more extensive realignment. In a study of the results of thirty-three replacements in twenty-seven patients who had primarily patellofemoral arthritis, Mont et al.46 reported twenty-eight excellent results, one good result, and one poor result at a mean of eighty-one months postoperatively. The mean Knee Society objective score increased from 50 points preoperatively to 93 points postoperatively. Resurfacing of the patella in total knee replacement is a controversial issue, even when the patella is arthritic. A number of surgeons have reported routinely leaving the patella unresurfaced during knee replacement surgery. Thompson et al. took the concept to the extreme when they performed thirty-three total knee replacements without patellar resurfacing in thirty-one patients with isolated patellofemoral arthritis in whom the pain, by definition, could have come only from the patellofemoral joint47. At twenty months postoperatively, twenty-one knees were pain-free and twelve knees were occasionally painful. The average range of flexion was 104°. None of the patients required revision surgery. Despite the success of total knee arthroplasty, many surgeons consider it to be too big a sacrifice of healthy tissue and too great a surgical dissection for a patient with disease involving mainly one compartment.
Anterior Transfer of the Tibial Tuberosity Maquet50 was the first to develop a procedure that moves the tibial tuberosity anteriorly, with his eponymous operation that elevates the tuberosity by 2.5 cm. On the basis of in vitro studies, Ferguson et al.51 later proposed a variation on Maquet's operation, whereby the tibial tuberosity was elevated just 0.5 in (1.27 cm). Schepsis et al.52 recommended an elevation of 1.6 to 1.8 cm to compensate for the expected settling of the construct. Subsequent investigators have recommended elevations as low as 1.25 cm53 and even 1 cm54,55 on the basis of in vitro considerations. Ferrandez et al.55 noted that elevation of the tibial tuberosity can paradoxically increase stresses on the proximal portion of the patella, particularly when it is elevated >1 cm. Using in vitro measurements, both Nakamura et al.54 and Ferrandez et al. found an elevation of >1 cm to be counterproductive with regard to patellofemoral stresses. The Maquet operation has been reportedly associated with a number of complications, most notably skin necrosis, cracking of the osteotomy fragment, patellar tendinitis, and the development of a painful prominence at the level of the tibial tuberosity52. These problems have largely been addressed by lengthening of the osteotomy fragment that is elevated, as this minimizes the angulation required for a given elevation. Because Maquet's operation has been used for a wide variety of patellofemoral conditions and because the results have not always been correlated with the etiology of the pain or the specific location of the arthritis, the clinical results of the operation for patellofemoral arthritis can be difficult to ascertain. Heatley et al.56 noted that, of fourteen knees treated with a Maquet operation for patellofemoral arthritis, six were rated as good to excellent, three were rated as fair, and five were rated poor at six years postoperatively. Jenny et al.57 evaluated sixty-five patients who had undergone a Maquet procedure for a variety of conditions and found that the forty-eight patients with patellofemoral arthritis had the best results at an average of eleven years. In neither study was the exact location of the arthritis within the patellofemoral joint specified. Division of the patients into subgroups according to the location of the chondral lesions would have been useful. Engebretsen et al.58 reported on thirty-eight patients treated with the Maquet procedure. Of thirty-three patients who were available for follow-up at a mean of five years, ten had improvement, seventeen had no change, and six were worse off. The patients with improvement were noted to have "Grade III and IV" cartilage changes primarily involving the lateral facet. Over the last twenty years, Maquet's operation has diminished in popularity in Europe59, with some surgeons actually reversing the procedure23. However, a variation on the Maquet procedure—anteromedial displacement of the tibial tuberosity—increased in popularity in the United States over that same period of time.
Anteromedial Transfer of the Tibial Tuberosity This operation has the disadvantage of not allowing the same amount of anterior displacement as Maquet's procedure permits, and it displaces the tibial tuberosity medially even in patients in whom the need for such medialization is unclear (for example, patients with a normal quadriceps [Q] angle)61. Medial displacement of the tuberosity in this setting may increase the medial femorotibial forces, resulting in pain in that compartment. This procedure does offer a number of advantages. A single osseous cut achieves both anterior and medial displacement in patients who need this combined effect. A bone wedge is not required at the osteotomy site to maintain the displacement. If the screws used for fixation of the shingle are oriented perpendicular to the plane of the osteotomy, both the drill and the screws will be oriented toward the medial aspect of the posterior part of the tibia and the popliteal space, where injury to the popliteal artery or vein is unlikely62. Most importantly, in the setting of patellofemoral arthritis this operation shifts the patellofemoral contact area medially, an advantageous displacement when the arthritis is located on the lateral aspect of the patella. This osteotomy presents technical pitfalls. It requires two cuts. The first cut involves all but the most proximal portion of the tibial tuberosity. That cut is angled in an anteromedial-to-posterolateral direction, with care taken to protect both the anterior tibial artery and the deep peroneal nerve posteriorly. The second cut begins at the most proximal and lateral aspect of the first cut and is oriented toward the most proximal portion of the tibial tuberosity. If the surgeon fails to carry out this second cut and chooses instead to carry the first cut all of the way to the top of the tuberosity, the cut will involve a large part of the proximal tibial metaphysis. If the tibial tuberosity were displaced 11 mm along a 45° degree plane, which is a substantial displacement, this would lead to 8 mm of medial displacement and 8 mm of anterior displacement. Ateshian and Hung7 calculated that this would result in only a 10% reduction in stress. This would explain why the procedure is not well suited for the treatment of global arthritis of the patellofemoral joint63, although the correlation between clinical success and stress reduction has yet to be established. Moreover, an 8-mm anteromedial displacement of the tibial tuberosity would lead to a 4.5-mm medial displacement of the patellofemoral contact area7, which, in some cases, may be enough to provide clinical improvement. Greater anterior advancement is not necessarily beneficial. For example, Takeuchi et al.64 performed an oblique osteotomy (with a 70 x 15-mm shingle) on seven specimens, and, using pressure-sensitive film, found that an elevation of 10 mm provided greater stress (force/area) reduction than an elevation of 20 mm. Indeed, the diminished forces at elevations of 20 mm were largely (and negatively) offset by the diminution in contact area. Pidoriano et al.63 correlated the results of this procedure with the specific location of the arthritic lesions. They noted the best results in patients with arthritis isolated to the lateral portion of the patella, even when there was a complete loss of articular cartilage at that site, and the worst results in patients who had diffuse involvement of the patella, extensive involvement of the trochlea, diseased cartilage at the proximal portion of the patella, and crush injuries65. Complications associated with this operation include postoperative fracture of the tibial shaft and nonunion of the osteotomy site. The osteotomy incorporates a substantial portion of the proximal tibial cortex, thus greatly diminishing the tibia's ability to withstand torque. Stetson et al.66 reported that six patients and Bellemans et al.67 reported that four patients sustained a fracture of the tibia at the distal junction of the osteotomized tibial tuberosity and the tibial shaft. All fractures occurred as the patients progressed to full weight-bearing status. Bellemans et al. recommended that patients remain nonweight-bearing for eight weeks. In the series reported by Stetson et al., two of the six fractures occurred after eight weeks, and the authors therefore recommended that full weight-bearing not be allowed until there was radiographic evidence of osseous healing. The screw heads may be palpable and tender, and one or both screws may need to be removed after healing of the osteotomy site. Removing a partially threaded cancellous screw can be difficult as the threads may not be able to cut back through bone that has grown along the nonthreaded portion of the screw, and use of a fully threaded screw may be advisable.
Patellofemoral Replacement In 1975, Aglietti et al.72 introduced a dome-shaped cobalt-chromium-molybdenum patellar component that was identical in shape to the patellar button of their total knee replacement. They did not report the results of clinical follow-up. Worrell designed a cobalt-chromium device and reported short-term follow-up results in 197973 and then again reported results in 198674. Of fourteen knees in thirteen patients (eighteen to thirty-eight years of age) followed for a mean of five and a half years (range, one to eight years), two had an excellent result; one, a good result; seven, a fair result; and four, a poor result. The best results were in patients over the age of forty years who had "extremely poor quadriceps function." The implant has not been reported on by other investigators, to our knowledge. The concept of a metallic implant articulating with the cartilaginous trochlea has been unappealing to the orthopaedic community because of concerns about harming an intact trochlea or, conversely, not addressing chondral lesions already present in the trochlea. In 1979, Lubinus75 and Blazina et al.76 introduced separately the concept of a patellofemoral replacement whereby both the patella and the trochlea were resurfaced. Despite some confusion in the literature46, this operation is separate and distinct from a simple patellar resurfacing. The procedure requires less surgical dissection than a total knee replacement, removes less bone, preserves the femorotibial compartments as well as the cruciate ligaments, does not necessitate blood transfusion, and can potentially be less expensive. Patellofemoral replacement surgery has not been widely accepted. The original descriptions of the procedure did not include strict criteria, technical pitfalls were not yet appreciated, and little emphasis was placed on realignment of the extensor mechanism of the knee. Consequently, reports pertaining to the earliest designs showed disappointing results. In Europe this led to efforts to redesign the implant and improve the operative technique, and in the United States most surgeons simply abandoned the procedure. The literature of the last fifteen years has been far more encouraging. Cartier et al.77 reported the results at an average of four years after patellofemoral replacements in seventy-two patients, thirty-six of whom had a concomitant femorotibial unicompartmental replacement and one of whom also underwent a tibial osteotomy. Sixty-one patients (85%) had a good-to-excellent result according to the Mansat (0 to 20-point) scale78. Another five patients (7%) had a good-to-excellent result after undergoing a remedial procedure (additional patellar realignment and exchange of the patellar button for a smaller size). In 1995, Argenson et al. reported the results of sixty-six replacements reviewed at an average of 5.5 years79. Dividing their results by etiology, they noted a good result in twenty of twenty-two patients with malalignment and dysplasia, nineteen of twenty patients with posttraumatic arthritis, and seventeen of twenty-four patients with arthritis of unknown etiology. In 1996, Krajca-Radcliffe and Coker80 reported a good-to-excellent result in fifteen of sixteen patients followed for an average of 5.8 years after patellofemoral replacement. Mertl et al.81 reviewed the outcomes of fifty patellofemoral replacements at an average of three years (with twenty-two followed for at least four years) and, using the Guepar rating tool82, found 34% (seventeen) very good, 48% (twenty-four) good, and 18% (nine) poor results. Of the nine failures, five pertained to the femorotibial compartments; two, to a complex regional pain syndrome; one, to an infection; and one was in a patient with a Workers' Compensation claim whose pain remained unresolved. Arnbjornsson and Ryd83 found that, at seven years after patellofemoral replacement, 75% (eighty-five) of 113 patients were satisfied with the result, 58% (sixty-six) of the 113 walked without assistive devices, and 44% (fifty) of the 113 had no or only occasional knee pain. Predictably, they found the poorest results in patients who had the nonspecific diagnosis of chondromalacia. De Cloedt et al.84 followed forty-five patients for three to twelve years after patellofemoral replacement and found that only 43% (nine) of twenty-one patients with arthritis and no malalignment or dysplasia had a good result, with the main cause of failure being degeneration of the femorotibial compartments. In contrast, 83% (twenty) of twenty-four patients with so-called patellofemoral instability and/or trochlear dysplasia had a good result. Kooijman et al.85 followed forty-five patients for ten to twenty-one years after patellofemoral arthroplasty. Fifteen patients required another operation (most commonly a soft-tissue operation such as a lateral retinacular release) soon after the index procedure, and twelve underwent either a tibial osteotomy or a total knee replacement at an average of fifteen years. However, two-thirds (thirty-three) of the forty-five patients still had the patellofemoral replacement at the time of final follow-up (at an average of seventeen years). The poor results reported after patellofemoral replacement have a common theme: failure to appreciate present or incipient femorotibial arthritis. Arthritis is more likely to develop in the remainder of the knee in a patient with an incomplete evaluation and in a patient in whom the patellofemoral arthritis does not have a clear origin, such as malalignment, dysplasia, or trauma.
Autologous Chondrocyte Implantation Recently, Minas and Bryant89 reported more favorable results with autologous chondrocyte implantation. They investigated a group of forty-five patients who had patellofemoral arthritis, with or without femorotibial arthritis. Eight patients had isolated patellar arthritis, nine had trochlear arthritis, four demonstrated patellar and trochlear arthritis, and the remainder exhibited arthritis in two or more compartments. The authors noted that, at an average of two years postoperatively, the patients with patellar arthritis, trochlear arthritis, and "patella plus trochlea plus weight-bearing condyles" (involvement of both the patellar and the trochlear side of the patellofemoral articulation as well as of the weight-bearing portion of one or both femoral condyles) "all had marked improvement in pain relief and function." There were eight graft failures in the patellofemoral compartment. Minas and Bryant noted clinical failures in five of eleven patients with a Workers' Compensation claim. Autologous chondrocyte implantation is expensive but may eventually be cost-effective if it provides long-term pain relief. Examining costs per quality-adjusted life-year, Clar et al.90 attempted to compare the cost-effectiveness of autologous chondrocyte implantation procedures in the knee with microfracture and mosaicplasty operations, but they found the results to be inconclusive because of a lack of sufficient long-term data. Derrett et al.91 also investigated the costs per quality-adjusted life-year of both autologous chondrocyte implantation and mosaicplasty. They found that both operations fell below "an implicit English funding threshold"—in other words, they were not (yet) cost-effective according to the available follow-up data. Longer follow-up and clinical trials comparing autologous chondrocyte implantation with other options for treatment of patellofemoral arthritis are needed before this option can be recommended as a standard procedure.
Patellectomy The popularity of the procedure has gone through cycles. In 1909, Heineck92 condemned it, stating that, on the basis of his experience with five patients, "its removal is invariably followed by impairment of power, by some functional loss." Brooke93, in 1937, reported good results in thirty cases, and Hey Groves94 supported Brooke's opinion that the procedure was beneficial. In 1948, McFarland95 went so far as to recommend the procedure for simple recurrent patellar dislocation. However, in 1949, Scott96 reviewed a series of seventy-one patellar fractures treated with patellectomy and found that 60% of patients reported so-called giving-way of the knee and 90% of patients still had pain. Since then, the literature has been inconclusive regarding this procedure. In 1969, Castaing et al.97 reported that forty-six of sixty-one patients had a good-to-excellent result at an average of five years after a patellectomy. The patellectomy was carried out with use of a vertical incision over the patella. A nearly full-thickness flap of quadriceps tendon was turned down and was sutured into the patellar tendon, and the medial and lateral retinacula were sutured over this turn-down construct. In a subset of seventeen patients with arthritis, just six patients had a good-to-excellent result, with the poorest results found in those with femorotibial disease. Overall, quadriceps strength, the active range of motion, and knee stability were judged to be acceptable. Stair descent tended to be a source of problems. Heterotopic ossification about the patellectomy site (considered to be "patellar regeneration" by the authors) was noted in two patients, but it had no correlation with results. Recovery tended to be long, and a number of patients noted continued improvement over the follow-up period. Compere et al.98 reported on twenty-nine knees followed for an average of approximately seven years after patellectomy. The patients were young (average age, 43.5 years) and presented with various degrees of arthritis. The fibers at the dorsum of the patella were maintained while the patella was everted and enucleated. The medial and lateral borders of the quadriceps and patellar tendons were sutured together to fashion a tube. The vastus medialis was advanced and sutured onto this tube. Ninety percent (twenty-six) of the twenty-nine knees were rated as having a good-to-excellent result. "Symptomatic calcification in the patellar tendon" developed in one patient; it was surgically removed, and the patient eventually had an excellent result. De la Caffinière99 noted good results in a cohort of seventy young patients (thirty to sixty years of age) with patellofemoral arthritis. Addressing the issue of quadriceps weakness and extensor lag following patellectomy procedures, he noted that final quadriceps strength could not be assessed less than two years following the operation. Baker and Hughston100 noted that nineteen of twenty patients with arthritis of the knee were satisfied at an average of fourteen years following treatment with the Miyakawa technique101, which requires that a partial-thickness strip of quadriceps tendon be turned down over the void left by the patella. In addition, the vastus lateralis and vastus medialis are advanced, crossed over each other, and attached to the quadriceps tendon. In a more recent review, Lennox et al.102 found the poorest results in their patients who underwent a patellectomy for arthritis. (Not all of their patients underwent the patellectomy for that indication.) They reported a good result in only 54% (twelve) of twenty-two patients with arthritis, with 27% (six) of the twenty-two patients reporting that they felt worse than they had preoperatively. This was a retrospective analysis of patients who had been operated on twelve to forty-eight years earlier, with the charts having been culled from hospital records. The evaluation was carried out mostly by telephone. The article does not name or describe the surgical technique(s). A shortcoming of all of the above studies is a lack of description of the anatomic location of the arthritis. It is not clear, for example, what percentage of patients had arthritis limited to the patella or how often arthritis was present on both the patella and the trochlea. We believe that a patellectomy can relieve symptoms and improve function when the advancement of soft tissues adequately compensates for the void left by the patellectomy. Although logic would dictate that patellectomies performed for the treatment of patellofemoral arthritis would be more successful when the arthritis is limited to the patella, this has not been studied, to our knowledge. A major drawback of a patellectomy is that, for all practical purposes, it is irreversible, although perhaps less so than other resection arthroplasties.
Removal of Subchondral Bone, Facetectomy, Thinning, and Denervation In a procedure termed spongialization by its originators (Ficat et al.103), the subchondral bone is removed down to cancellous (spongy) bone. The operation was also described by Marmor104 and is still used by some in lieu of patellar resurfacing during total knee replacement arthroplasty105. When the patellofemoral arthritis is limited to the lateralmost portion of the compartment, consideration can be given to removing 1 to 1.5 cm from the lateral aspect of the patella (a so-called facetectomy). Yercan et al.106 followed eleven patients for an average of eight years after such a procedure and noted a significant increase in the average pain score (p = 0.04) and in the average Knee Society score (p = 0.02) (based on the findings of a physical examination)107. The average Knee Society functional score (based on walking and stair-climbing) also improved. In order to diminish the stresses on the patellofemoral joint, bone can be removed from the center of the patella to decrease its thickness. Both the removal of the layer and the reattachment of the two remaining portions may be technically difficult, especially since care must be taken not to further damage the articular surface. Nerubay and Katnelson108 performed the procedure on fifteen patients who had demonstrated patellar malalignment and followed them for an average of three years. Twelve patients had a good-to-excellent result. Vaquero and Arriaza109 used a double saw to remove 7 mm of bone from the center of the patella and noted a diminution of patellofemoral stresses when they applied Fuji film to the patellofemoral joint. Following this operative procedure, there may not be much osseous bed left for a prosthetic replacement if one is needed at a later time. The patella is innervated by multiple superficial sensory nerves, including the medial cutaneous nerve of the thigh, the lateral femoral cutaneous nerve, the medial and lateral retinacular nerve, and the anterior femoral cutaneous nerve110. Division of these nerves can diminish pain emanating from the patella but is likely to be less effective for trochlear lesions. No formal study of surgical denervation has been carried out in the specific setting of patellofemoral arthritis, to our knowledge.
If autologous chondrocyte implantation can be used to fill discrete defects, it is possible that similar technology could be utilized for larger surfaces. Ateshian and Hung7 investigated the possibility of resurfacing the entire patellar articulation with anatomically shaped molds to contour chondrocyte-seeded gels into the desired shape. They found that dynamic loading of the construct greatly increased its strength, to the point where the mechanical properties of the articular cartilage approached those of the native tissue. To anchor the cartilage into bone, it may be feasible to engineer cartilage cells that are already anchored into an osseous substrate. Ateshian and Hung experimentally used bovine bone for this purpose. These large constructs pose challenges to nutrient diffusion in the cartilage that will need to be solved before large, viable areas of articular cartilage can be produced.
A number of challenges remain in the field of patellofemoral arthritis. In order to improve investigations of treatments, the orthopaedic community needs to accept a validated outcome tool. The term patellofemoral arthritis itself requires greater anatomic precision, as arthritis localized to one portion of the patellofemoral compartment may behave differently from global patellar and trochlear arthritis. Clinically, the challenges to the surgeon remain the identification of patients whose symptoms are truly the result of isolated patellofemoral arthritis and the selection of a viable surgical operation for those patients. The lack of uniform reporting makes it difficult to recommend one procedure over another at this time. Operations that shift the patellofemoral contact area medially are recommended for young patients with arthritis that is limited to the lateral aspect of the patella, whereas joint replacement surgery remains the best option for older patients who have diffuse arthritis involving both the patella and the trochlea.
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Abstract
Introduction
