Patellofemoral Arthroplasty: A Useful Option for Recalcitrant Symptomatic Patellofemoral Arthritis

Patellofemoral Arthroplasty: A Useful Option for Recalcitrant Symptomatic Patellofemoral Arthritis Wayne B. Leadbetter, MD, and Michael A. Mont, MD Patellofemoral arthroplasty is a compartmental salvage procedure for symptomatic advanced isolated articular degeneration and arthritis. Despite a long historical precedent, until recently attempts at prosthetic resurfacing of the patellofemoral joint have met with little acceptance by the orthopedic community. Presently, increased awareness of the functional importance of the patellofemoral joint and the prevalence of pain and disability related to patellofemoral degeneration, coupled with the failure of commonly prescribed measures to relieve some patients, has spurred a rethinking of this issue. Better patient selection combined with improved prosthetic design and operative technique are contributing to published outcomes that equal or exceed many operative alternatives. Although total knee arthroplasty remains a reliable operation for older patients, younger and midlife patients may prefer a patellofemoral arthroplasty as a conservative option that retains anterior cruxiate ligament function. Semin Arthro 20:148-160 © 2009 Elsevier Inc. All rights reserved. KEYWORDS arthroplasty, knee arthritis, knee pain, patella pain, patellofemoral replacement

P

atellofemoral arthroplasty (PFA) is a salvage operation for refractory symptomatic severe chondrosis and arthrosis. By definition, a typical PFA patient has failed previous nonoperative and operative treatment options and continues to suffer unacceptable disability. As in the hip joint, attempts to prosthetically salvage the degenerative patellofemoral joint were initially a type of hemiarthroplasty that resurfaced only the patella facets.1 Blazina described the first clinically useful PFA in 1979. His original design with modifications (Richards I and II, Smith and Nephew, Memphis, Tennessee) achieved minor success for many years, particularly in France.2 However, these early-phase prosthetic devices gathered little interest in the United States because of less sophisticated bioengineering design, a lagging appreciation for the clinical importance of the patellofemoral joint, and less predictable outcome, particularly, as this occurred at the same time as the beginning of the modern total knee arthroplasty (TKA) era. The patellofemoral joint became known as the “forgotten joint.” Why then has there been an apparent resurgent interest not only in patellofemoral prosthetic salvage, Department of Orthopedics, Center for Joint Preservation and Replacement, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, Baltimore, MD. Address reprint requests to Wayne B. Leadbetter, MD, Department of Orthopedics, Center for Joint Preservation and Replacement, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, 2401 West Belvedere Avenue, Baltimore, MD, USA. E-mail: [email protected]

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but also in the functional importance of conserving the patellofemoral articulation both in isolated disease and TKA? The answer lies in the current better understanding of the contributing factors, diagnosis, and treatment of symptomatic patellofemoral articular degeneration. Most importantly, considerable progress has been made in optimizing prosthetic design and in the appropriate application of these devices. The following discussion will briefly review the evolution, indications, potential complications, factors in patient selection, key aspects of operative technique, and postoperative outcome of current PFA. As well, the author will touch on some of the controversy engendered by this treatment option vs TKA. It is proposed that at the present time, modern PFA plays a useful and versatile role in the current treatment algorithm of patellofemoral degenerative conditions (Fig. 1).

The Rationale for PFA As noted, the perceived need for prosthetic salvage alternatives for the patellofemoral joint is not a new development and preceded TKA.1 The present rationale or need for a prosthetic patellofemoral resurfacing operation stems from multiple observations. These include the prevalence and incidence of isolated patellofemoral arthritis (PA) and degeneration, and the negative effect of patellofemoral pain (PFP) on knee and lower extremity function. In addition, the importance of con-

Patellofemoral arthroplasty

Figure 1 Avon patellofemoral prosthesis (Stryker, Mahwah, NJ, USA). This prosthesis typifies the present evolution in PFA design. Platformed on the Kinamax TKA (Howmedica, Limmerick, Ireland) note the less contrained trochlea component for better patella capture and tracking, low profile, improved fixation and patella button that may be either asymmetric for stability or symmetric for more universal revision and more forgiving tracking. (Color version of figure is available online.)

serving optimum extensor mechanism function of the knee joint is now established, especially in those patients who ultimately require a TKA.3,4 Although there are several operative approaches, virtually all of these options for the painful degenerative patellofemoral joint have limitations and significant outcome failures.5 Finally, there has been a re-examining of the outcomes, patient satisfaction, and risks associated with TKA.6-8 Renewed interest in PFA is consistent with a persistent trend toward knee joint conservation using compartmental salvage methods.9

Prevalence of Isolated Patellofemoral Degenerative Disease Patellofemoral degenerative disease encompasses a spectrum of articular wear from severe chondrosis (Outerbridge III/IV with predominantly articular cartilage involvement) to advanced arthrosis (Outerbridge IV with exposed eburnated subchondral bone and remodeling). However, the Outerbridge classification technically refers to the morphologic stages of chondral injury or chondromalacia, whereas such classifications as the Ahlback10 or Kellgren and Lawrence11 are preferred to judge arthritis viewed on plain radiographs. Patellofemoral arthritis is often used as an encompassing term referring to all presentations of advanced articular wear.5 Patellofemoral joint pain is the most common problem involving the knee, affecting 25% of the general population.12 Isolated PA is found in 5%-10% of patients who present to physicians for diagnosis and treatment of arthritic knee pain.13 It is present in up to 15% of patients who are older than 60 years.14 When studies were stratified for patients over

149 50 years old with symptomatic osteoarthritis of the knee, the prevalence of isolated patellofemoral disease ranged from 5% to 8%.15,16 Because most reports to date use only plain radiographic criteria for the diagnosis of PA, the reported prevalence does not account for those patients with significant articular lesions documented by arthroscopy and magnetic resonance imaging (MRI). A common pathoetiology of patellofemoral degeneration is the overuse and overload exposure created by years of running and jumping athletic activity and some forms of fitness training such as knee lunges, squat weight-lifting, or high-impact step aerobics.17 The malaligned or dyplastic patellofemoral joint is particularly susceptible to this cumulative microinjury.5,18 Patients are commonly female and present in midlife with painful crepitation and bent knee disability. In our experience, despite conventional nonoperative and operative intervention, a large number of these patients will eventually progress to unacceptable daily pain and disability. Today, as with the prevalence of anterior cruciate ligament injury, these complaints may be more common because of the greater female participation in competitive and fitness athletics. These factors along with anatomic findings such as excessive femoral anteversion with compensatory external tibial torsion may be reflected in the greater bias of female patients receiving PFA.19-21 Furthermore, published prevalence figures for PA do not take into account the patients who can be expected to fail some type of earlier patellofemoral operative treatment for focal chondral injury or degenerative disease. For instance, the reported failure rate for autogenous cartilage implantation on the patella and/or bipolar trochlear lesions ranges from 4% to 29%, depending on defect traits and duration of follow-up.22-24

Functional Impact of Patellectomy, Extensor Mechanism Weakness, and PFP PFA was first introduced as an alternative to patellectomy.1 The patellectomized patient complains of knee extension weakness, fatigue, buckling, and pain.25 The power and functional endurance of knee joint extension depends on the integrity of the quadriceps muscle and the fulcrum provided by the patella sesamoid bone.26 Quadriceps torque decreases 20%-70% after patellectomy.27,28 Quadriceps muscle weakness and decreased voluntary muscle activation directly correlates with arthritic knee pain and related community disability.29 The effect of patella loss persists even after TKA and has a marked negative effect upon TKA outcomes.30 Diminished patella function negatively affects normal gait kinematics with alterations in both tibiofemoral joint stability and load distribution.30,31 Patients with PFP display deficiencies in knee joint position sense.32 Studies of patients with PFP have revealed protective maladaptations in the kinematics of stair descent.33 PFP slows walking speed and changes tibiofemoral loading because of a shortened stride and gait cadence.34 Patients with PFP suffer from increased stress across the patellofemoral joint during walking.35 Successful operative treatment of PA must succeed in reversing or significantly reducing these dysfunctional effects.

W.B. Leadbetter and M.A. Mont

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Limitations and Failure of Operative Alternatives to PFA All currently advocated operative treatments for advanced patellofemoral joint degeneration and arthritis remain con-

Table 1 Limitations of Current Operative Alternatives for Salvaging Patellofemoral Arthritis Procedure Arthroscopic chondroplasty

Limitations

Thermal articular cartilage necrosis,38-40 Unreliable functional improvement41 Lateral release Unreliable outcomes42 Lesion location and alignment specific May destabilize the patella43 Biological Age restrictions23,24,44 restoration/ Long recovery22-24 regeneration Not indicated for bipolar lesions24 Technically demanding37 Often requires unloading anteromedialization tibial tubercle osteotomy22,23 Cost22,24 Histologic success45,46 Off label in the patellofemoral joint22 Microfracture Unpredictable benefit Technically not suited to the patella24 Not indicated for large or bipolar lesions24 May jeopardize outcome for autogenous chondrocyte implantation47 Lesion location and alignment Unloading dependent48 anteromedialization Not indicated in crush injury48 tibial tubercle osteotomy 6 wks nonweight bearing post operation22 Technically sensitive Partial lateral Lesion location and alignment facetectomy dependent49 Impact on future patella resurfacing in patellofemoral arthroplasty/ total knee arthroplasty Seventeen percent failure shortterm50 Patellofemoral Requires extensor mechanism arthroplasty balancing and/or realignment51,52 Tibiofemoral joint arthritic progression51,53 Potential medial facet impingement in knee flexion52 Persistant pain or effusion54-56 Total knee Potential for serious arthroplasty complications57,58 Revision risk59,60 Durability in patients under 507,8 Sacrifice of the anterior cruciate ligament9 Functional compromizes61

troversial concerning indications, patient selection, technique, and outcome reliability.5,36 Complications of various patellofemoral surgeries have been well-documented.37 The limitations of common options for operative salvage for patellofemoral joint degeneration are listed in Table 1. The problem of outcome reliability has long been appreciated.62,48,114 Commentary referring to the patellofemoral joint as “the forgotten joint,” pejorative labeling of PFP as the “low back pain” of the knee, and caveats that “there are no heroes in patellofemoral surgery,” reflect a pessimistic precedent for the success of operative treatment.54 To be successful, an operation must be directed at the correct dominant pathoetiology. However, in PA there are often multiple factors contributing to onset, progression, and disability. All of these factors affect the patellofemoral joint by the promotion of excessive (eg, malalignment, excessive femoral anteversion) or deficient (eg, atrophic) mechanical load on articular surfaces. Adding to this challenge is the observation that the patellofemoral joint is a hostile environment, particularly for biological restoration. It is highly loaded, has minimal skeletal constraint, is functionally dependent on the integrity of muscle forces, and soft tissue balance. It is highly prone to dysplasia and congenital variation and is dynamically influenced by limb skeletal alignment. Is it any wonder that no one operation will regularly solve any 1 particular patellar problem? Published series tend to be retrospective with short-term (⬍5 years) follow-up, rarely achieving over 80% good results and even fewer excellent outcomes.41 Besides the temporary relief of degenerative related inflammatory events afforded by joint debridement, operative treatments have focused upon relieving patellofemoral degenerative pain by improving the distribution of forces on the joint by realignment by osteotomy. This reduces the articular surface overload. Alternatively, increasing available joint surface contact, thereby decreasing load per unit area, ie, pressure, can be accomplished as with biological restoration or prosthetic resurfacing. Arthroscopic debridement with mechanical shavers or thermal devices continues to be a mainstay in the initial operative treatment of patellofemoral chondral wear.63 However, there are major concerns for the potential for iatragenic damage to healthy articular cartilage.38,39 The use of such modalities is extremely technique-dependent.23 Studies of diffuse patellar chondral debridement usually document moderate short-term symptomatic and functional improvements that are even less achievable in patients with patellofemoral malalignment and advanced grades of chondrosis.41 The patellofemoral joint is not as responsive as the tibiofemoral joint to this form of treatment.40 The real limitation of such isolated treatment is that it does not address underlying promoting factors such as biomechanical malalignment or dysplasia. Thus, as Teitge64 has noted, “removal of articular cartilage is tantamount to accelerating the rate of arthritic development.” Today, most younger patients with early stages of symptomatic patellofemoral degeneration (ie, chondromalacia patella) that is refractory to nonoperative management are of-

Patellofemoral arthroplasty

Figure 2 Plain radiograph, left knee, patellofemoral view. Note inaccurate apparent normal patellofemoral alignment and morphology due to too much knee flexion (Settegast technique).

fered a “conservative” arthroscopic procedure. One highly abused and overused approach is to perform a lateral retinacular release. Often performed in the presence of unrecognized trochlear dysplasia and significant extensor mechanism malalignment (ie, tibial tuberosity-trochlear distance ⬎ 15 mm), this procedure has been found to be very ineffective in relieving arthritic pain. At its worst, lateral release may further destabilize coinicident patellofemoral instability.42,43 To achieve any success, invariably the patient must continue to be compliant after surgery with such measures as weight loss, behavior modification, and physical therapy as part of a comprehensive multimodal treatment program.65 Furthermore, although a majority of patients with PFP and/or moderate articular degeneration may respond and deserve an initial attempt at nonoperative and palliative measures,65,66 in our experience there remains a large number of patients who evolve to intolerable patellofemoral dominant disability. Post-traumatic diffuse chondral damage treatment does not have as good a prognosis for isolated debridement or unloading procedures.48,63 When acute patellofemoral trauma results in a crush to the articular surfaces, the disability of extensive PA can ensue very quickly, leaving few options other than patellectomy or arthroplasty. Patellectomy has fallen into disfavor as mentioned earlier. For example, in a series of 81 patients treated with patellectomy for isolated PA, Ackroyd and Polyzoides67 achieved only a good result in 53%, a fair result in 26%, and a poor result in 21% of 87 knees at a mean follow-up of 6.5 years (range, 2-22 years). Anteromedialization tibial tubercle osteotomy (AMZ) has remained a mainstay in the treatment of patellofemoral articular degeneration since 1983.68 However, lesion location and extent of patellofemoral malignment greatly influence outcome48 (Fig. 3). The operation is most effective in relieving pain in patients with bipolar lateral facet lesions accompanied by lateral patellofemoral malalignment.69 This group achieved 87% good to excellent results; however, in all other lesion locations the results declined (20%-55% good to ex-

151 cellent).48 Beck et al70 found that although AMZ may unload lateral trochlea lesions, the load effect upon the medial and central trochlea lesions is negligible or may increase. Such observations help in explaining why anteromedialization is unreliable and not recommended in post-traumatic crush injuries.48 Essentially, in a large number of cases, AMZ results will not be as good as those achieved by modern PFA.19 Similarly, although useful in select cases as an initial procedure, partial lateral facetectomy is best indicated for lateral patellofemoral dominant arthritis.49 Paulos et al50 reported a cumulative failure rate of 17% at 5 years after partial lateral facetectomy. Success with attempts at biological articular restoration in isolated PA has lagged behind success with femoral condylar lesions.71 The results of patellofemoral articular restoration using osteochondral grafts (mosiacplasty) with either autogenous or fresh frozen allografts is not well-documented, although such approaches in very young patients would appear reasonable, particularly with trochlear lesions.24 The technique is useful primarily in trochlear lesions and much less reported in patella facet lesions, presumably due to the dense recipient facet bone.72 Microfracture restoration is less helpful in the patellofemoral joint and requires a very specific rehabilitation including bracing.24 Recently, Minas et al47 have raised concern that antecedent microfracture may account for a higher failure rate of subsequent autologous cartilage implantation. Autogenous chondrocyte implantation (ACI) is not presently Food and Drug Administration approved for PFJ salvage.22 Although improving, such procedures can be technically demanding and costly. For example, biological restoration procedures such as ACI require relatively lengthy protected recovery.73 McNickle et al74 reported a 75% subjective patient satisfaction with ACI, with 17%

Figure 3 Same patient as in Figure 2. Patellofemoral computed tomography scan. Note pronounced proximal trochlear prominence indicating significant dyplasia and the true lateral patellofemoral malalignment.

152 unwilling to repeat the procedure. Age strongly correlated with failed ACI outcomes. One study reported good-excellent outcomes in only 55.9% in patients over 40 years of age.44 In one of only 2 existent reports, Mandelbaum et al75 claimed short-term “apparent” improvement at a mean follow-up of 59⫾18 months with ACI treatment of trochlea defects (mean size 4.5 cm2); however, there were no bipolar lesions. Minas and Bryant23 reported a 71% good to excellent result with patellofemoral ACI. However, while the lesions were extensive with a mean size of 4.86 cm2 on the patella and 5.22 cm2 on the trochlea, only 4 knees had both involved, ie, kissing lesions. These were extensive procedures with 64% of patients requiring either tibial tubercle osteotomy or high tibial osteotomy to unload and protect the implantation. Biopsy analysis of graft tissue revealed that the morphology and genetic expression of the reparative tissue differed markedly from normal articular cartilage.45,46 In summary, efforts to surgically treat the patellofemoral joint with present biological restoration techniques often appear compromised by the inherent hostile force/load milieu, distortions of joint congruency, and lack of reliable constraints.64 The Argument Against Total Knee Arthroplasty vs PFA in Younger Patients TKA can achieve marked improvement in younger patients with severe tricompartmental arthritis.76-78 Lonner et al61 reported a 91% good to excellent objective outcome in 32 knees in patients 40 years of age or younger who had a mean follow-up of 7.9 years. However, functional outcomes on the knee society score (KSS) were good to excellent in only 50% of patients. Futhermore, these results depend upon the reliability and validity of the KSS which has been called into question.43 Noble et al79 reported limitations in functional activities such as moving laterally, turning, carrying loads, playing tennis, and gardening in 52% of patients after TKA compared to 22% in age-matched patients who had no reported knee complaints. It was concluded that only about 40% of this deficit could be accounted for by normal aging effects. The decrease in muscle strength 1 month after TKA can be as high as 60%, and deficits of 20%-30% (compared with the contralateral limb or with health controls) may persist for several years.80 As many as 7%-19% of patients experience residual anterior knee pain when TKA is performed for isolated PA.81,82 The residual detriment to knee joint kinematics, stability and ligament balance caused by loss of the anterior cruciate ligament, and the required bone resection in present-day TKA has been documented.9 In older patients with isolated PA, the results of TKA have been reported as generally excellent with a range of 90%-95%.16,81-83 However, in these 4 reports, the mean patient age was 70 years (range, 47-88 years) and mean follow-up was only 6.4 years (range, 3-11 years). Lateral release was required in 27%-68% of knees. There was no assessment of specific recreational activity or significant quality of life limitations as previously mentioned by Noble et al.79 More recently, Meding et al84 attempted to compare the outcome of TKA vs PFA in younger patients. The study consisted of a retrospective cohort of 27

W.B. Leadbetter and M.A. Mont patients (33 TKAs) with average follow-up of 6.2 years (range, 2-12 years). The patients ranged in age from 38 to 60 years with a mean of 52 years. The authors used comparative historical data on PFA outcomes in 10 studies. Although the results of TKA were only “at least as good . . . compared to younger patients undergoing PFA,” it was concluded that TKA was the superior procedure. Without alluding to any first hand experience with PFA, the authors went on to make an indictment of PFA and labeled further comparative outcome study “questionably ethical”.84 There were many disturbing aspects to these conclusions. Notable, was the bias in the historical control. Of the 10 PFA papers reviewed, 6 involved first generation patellofemoral designs that have either been abandoned or totally redesigned85,86 and 2 papers reported the same prosthesis cohort only with longer follow-up.87-89 It was claimed that reported revision rates for PFA ranged as high as 51%, and that complications and/or reoperation rates were as high as 63%.84 This was grossly misleading, as the reported results for revision and complications of current widely used PFAs are much lower, ranging from 0% to 5% at a minimum 2 year to over 5 year follow-up.19,20,86,89,90,59 Long-term results with PFA reflect the limitations of selective compartment resurfacing. Ackroyd et al19 noted a 20% incidence of radiologic arthritic progression at 5 years or greater with the Avon prosthesis, but only 4% of patients required a revision operation at the time of follow-up. Cartier reported a survivorship of 75% at 6-10 years with the first generation Richards I/II prosthesis.2 The need for revision was primarily tibiofemoral disease progression, uncorrected extensor malalignment. Technical error, prosthetic loosening, wear, and infection were distinctly uncommon in contradistinction to various TKA experiences.91 Thus, an average of 75%-80% of patients continued to enjoy the benefits of isolated patellofemoral resurfacing while avoiding the technical and revision risks of modern day TKA. As of 2006 to the best of the authors’ knowledge, there have been 16 publications addressing PFA outcomes representing 773 patients (912 knees) who have a mean age of 56 years (range, 19-90 Table 2 Indications for Patellofemoral Arthroplasty 1. Degenerative osteoarthritis of the patellofemoral (ie, Outerbridge grade IV, loss of joint space with osseous spurring) 2. Severe activity of daily living disability referable to the patellofemoral joint and unresponsive to lengthy (>3 mo) nonoperative treatment and/or failed previous operations 3. Crush injury or post fracture patellofemoral arthritis 4. Extensive Outerbridge grade III chondrosis (ie, loss of joint space without osseous deformation of the patellofemoral joint space), particularly with pantrochlear, medial facet, or proximal half of patella distribution refractory to prior treatment 5. Failed extensor unloading procedure 6. Patellofemoral malalignment or dysplasia induced degeneration with correctible malalignment or extensor instability

Patellofemoral arthroplasty years), a mean follow-up of 6 years with a mean outcome of 88% improved function and pain relief (range, 42%-96%). The high number of patients and the persistent usage of PFA since 1979 tends to speak to its perceived value in salvaging isolated PA by some surgeons. The problems with the failed TKA is not to be downplayed. Revision rates for TKA have been correlated with younger age.7,8 Typically, TKA reports do not stratify results for specific activities and sports. Mont et al92 surveyed tennis players (mean age 64 years) with TKA at a mean follow-up of 7 years and found high subjective satisfaction, but cautioned that the accumulative effect on prosthetic survivorship of many years of such high performance activity has not been determined. One would assume that this cautionary advice would extend even more to a younger patient population. Yet, today more and more younger patients have high performance expectations that are tacitly encouraged by prosthetic consumer marketing. As we have seen no opinions that suggest that the recipient of a TKA at a younger age should be counseled not to expect at least 1 lifetime revision, the findings of Barrack et al57 regarding patient expectations after revision should be a concern to the surgeon. Generally, patients expect that their arthroplasty will last longer. More alarming was the finding that 66% disagreed with their surgeon as to the reason for failure and that only 69% were satisfied with their revision outcome.57 Revised TKAs have been noted to have a consistent failure rate of 10%-15% at five years.60 Feinglass et al93 have noted that TKA revision rates are growing rapidly. This would suggest that the present comparative outcome standard of TKA durability to which PFA is being held is faulty, ie, a large number of total knee arthroplasties placed in younger patients can be expected to fail. In contradistinction, Lonner et al58 has noted that revision of the failed PFA does not compromise TKA outcome. It should be noted that there are no reported cases of any failed PFA requiring a knee fusion or eventual amputation.94 The estimated mid-term accumulated failure rate for PFA has been calculated to be in the range of 20%-25%.51 However, Nicol et al55 in a review of 103 Avon PFA patients with a mean follow-up of 7.1 years (range 5.5-8.5 years) found a revision rate of 14%. Radiographic disease progression was noted in only the medial compartment in 7 of 89% of patients in the same study who had not required revision to TKA at a mean follow-up of 4.6 years.55 These results are comparable to reported mid-term failure rates of commonly advocated tibiofemoral joint unicompartmental arthroplasty, which ranges from 8% to 12%.95 Many younger patients fall into the expanded indication category for PFA for isolated severe grade III/IV Outerbridge articular disease related to trochlear dyplasia, trauma, or correctible extensor malalignment. The real prevalence of these cases is not well documented in the literature. However, based on reported failure rates of common operative treatments for patellofemoral chondral disease in previous discussion, between 14% and 30% of these cases will need further salvage. These patients will have been deemed suitable for joint conserving efforts.58 In our experience, neither surgeon nor patient is comfortable with the prospect of a TKA under these circumstances. Provided an informed choice, patients

153 invariably choose a PFA over a TKA and are willing to play the odds on durability vs risk, reserving a TKA as a backup. This is preferable to being told that, “you are too young for a TKA, so you’ll just have to live with your problem.” The issue is making available the choice. It is not surprising that some of the strongest advocates for PFA are also involved in biological restoration.96 If the surgeon has only 1 choice, ie, TKA, then the patient will only get that procedure. Although many arthroplasty and knee surgeons remain flexible on this issue,19,20,56,59,89,97 others are not.84 Ultimately, we believe the debate as to whether to choose a TKA or an apatellofemoral arthroplasty for the treatment of patellofemoral degenerative disease misses the point. The 2 operations should involve different subgroups of patients with marked differences in motive. TKA as reported today, can lay claim to efficacy in relieving disability in patients with isolated PA over age 65 years with reasonable hope of avoiding any further reoperations. TKA provides relief at least equal to PFA for advanced patellofemoral arthritic disease in younger patients, but at a cost. The challenge is how to help patients who suffer from symptomatic patellofemoral articular wear at an age when the survivorship of their TKA would have to extend well over 30 years. Unfortunately, younger patients who have failed repeated surgical interventions need a practical alternative to TKA for exactly the mid-term improvement that can be achieved with selective compartmental salvage. PFA has been documented to successfully address this challenge.2,19,20,59,86,89,90,98 Forestalling the “final solution” of a TKA in this group provides the option of electing to wait for TKA technology to advance to a time when operative error is more controlled(eg, navigation), bone resection is less, bearing surfaces improve even more, and cruxiate ligament function is routinely conserved. In over thirty years in practice, we have witnessed a time when no successful TKA existed to an era of tremendous advance in prosthetic innovation and efficacy. There is no reason to believe that these trends will not continue.

What to Consider Recommending or Performing a PFA A successful PFA operation must be predicated on accurate diagnosis, patient selection, surgical technique, and prosthetic design.21,51,52

Indications, Contraindications, and Additional Considerations The indications, contraindications, and additional considerations for recommending a PFA have been refined in recent reviews.21,51 (Tables 2-4). The best candidate for PFA has isolated arthritis related to trochlea dyplasia, extensor malalignment without instability or trauma.20,97,99 Such pathetiologies are less associated with tibiofemoral arthritic progression post PFA in the literature. All patients must complete a quality physical therapy program to eliminate unnecessary surgery and to demonstrate reasonable compliance with the

154 Table 3 Contraindications to Patellofemoral Arthroplasty 1. No attempt at nonoperative care or to rule out other sources of pain 2. Symptomatic arthritis involving the tibiofemoral joint greater than Kellgren-Lawrence I/II 3. Systemic inflammatory arthropathy 4. Osteoarthritis/chondrosis less than outerbridge grade III/IV 5. Patella infera 6. Uncorrected extensor malalignment or instability 7. Uncorrected tibiofemoral mechanical malalignment 8. Active infection 9. Fixed knee range of motion loss

surgeon’s expectations. In our practice, PFA is used as an initial treatment for isolated PA in very few patients over the age of 65 years. Younger midlife patients make up most cases. Often these patients have been psychologically, physically, and economically drained by the recovery burden of multiple failed prior procedures and have been told that nothing more can be done to help them. They are younger than 60 years of age and are unwilling to accept a TKA. The younger the patient, the more they must accept the bridging concept or “pre total knee” motive for PFA. Although activity achievement after PFA can be impressive, patients are counseled that PFA is a salvage only for activity of daily living. In patients under the age of 40 years, every effort is made to try to avoid PFA. That said, we have performed PFA successfully with short-term follow-up in patients as young as 25 years. The obese patient (BMI ⬎ 30) is never a good candidate for operative knee treatment.100,101 The risk of knee osteoarthritis increases by 36% for every 2 U of BMI (5 kg) of weight gain. Bariatric surgery results in a mean weight loss of 44 kg (43.7 kg); 89% of patients have been reported to achieve pain relief in at least 1 joint after undergoing bariatric surgery.102 If for some reason, voluntary weight loss or bariatric surgery is not an option, then in selected cases PFA may offer pain relief with less extensive operative morbidity. However, Leadbetter et al52 reported 2 cases of postoperative fall-induced patella tendon injuries in obese patients. To date, there has been no reported increased incidence of PFA prosthetic wear or loosening associated with the overweight patient.19,51

Salient Points on Patient Diagnosis and Selection The factors producing anterior and particularly patellofemoral arthritic pain are multiple, so likewise, are the solutions. Diagnosis of PFP presumes an accurate history and physical examination.66 Patients with symptomatic PA will share a great overlap of conditions that could produce similar symptoms coincident with an abnormal patellofemoral plain roentgenogram. In contradistinction, patients under the age of 50 often present with relatively normal radiographs, but can have prominent PFP and crepitation and are an even greater challenge for decision making.66,103 While much has been written about patient selection, not enough has been reported about surgeon selection. The op-

W.B. Leadbetter and M.A. Mont erating surgeon must be experienced or acquire training with various options for patellofemoral realignment because patients with PA often will present with coincident extensor malalignment and/or instability. Needed competency with arthroplasty salvage and revision technique is implied by the variety of postoperative complications and failures. It is incumbent upon the orthopedic surgeon to be familiar with the many nuances in the diagnostic evaluation of patellofemoral complaints, if inappropriate use of PFA is to be avoided.21 This includes both soft tissue as well as osseous assessment.104 Besides arthritis, a wide variety of conditions have been associated with the presence of PFP including transient synovitis, tendinopathy, quadriceps muscle inhibition, patellofemoral instability or malalignment, activity driven patellofemoral overload with loss of joint homeostasis, referred pain from the ipsilateral hip, discogenic pain, work or litigation-motivated secondary gain, psychogenic pain or depression, chronic regional pain syndrome, and neuromata.66,103,105 There is a frequent association between medial joint pathology and anterior knee pain. This must be differentiated by palpation, subjective symptom isolation, and selective imaging. As in unicompartmental arthroplasty planning, the “one finger test” can be helpful, where the patient is requested to put just 1 finger on the point of pain. Is important to ask the patient if their pain occurs mostly with bent knee activity, eg stair climbing, versus level walking. In our experience, patients with pain associated with both activities are not candidates for PFA. As with most operative treatment, it is prudent not to assure a complete relief of pain.

Radiologic Preoperative Assessment Because tibiofemoral osteoarthritic progression is the most common postoperative problem with PFA, an extensive delineation of the medial and lateral compartments of the knee must be performed preoperatively. At a minimum, initial radiographs should include a standing anteroposterior view Table 4 Additional Factors That May Adversely Affect or Contraindicate Patellofemoral Arthroplasty 1. Multiple antecedent procedures or extensive soft tissue trauma associated with severe residual quadriceps atrophy 2. History of arthrofibrosis with previous operations 3. Poor compliance with physical therapy 4. Anterior cruxiate ligament deficiency 5. Extensive chondrocalcinosis 6. A post-medial menisectomy knee 7. High demand patient 8. Unrealistic patient expectations 9. Psychogenic pain history, depression, or narcotic use 10. Primary osteoarthritis 11. Familial history of early onset knee osteoarthritis 12. Patella alta or infera 13. Workers compensation related complaint 14. A surgeon with lack of experience in patellofemoral pain diagnosis, arthroplasty, or knee extensor mechanism reliagnment 15. Complex regional pain syndrome

Patellofemoral arthroplasty

Figure 4 Operative image demonstrating potential for medial patella prosthesis impingement in knee flexion on the uncovered femoral condyle. (Photo courtesy of Wayne B. Leadbetter, MD) (Color version of figure is available online.)

(preferably a PA 45° Rosenberg view), true lateral, and Merchant patella view. If an adequate Merchant view cannot be reliably obtained, patellofemoral computerized axial tomography scans at 0°, 30°, and 60° flexion can provide useful information as to malalignment and subtle joint space loss106 (Figs. 2 and 3). The surgeon needs to be careful with patients who do not have a near neutral biomechanical axis. If there is concern about axial leg malalignment, a standing long leg film is required. The presence of 3°of genu varum accompanied by chondral wear and/or menisectomy creates significant load and pressure increases in the medial tibiofemoral compartment.107 Uncorrectable axial malalignment is a contraindication to PFA and an alternative for PFA must then be considered. Because malalignment corrections can require a huge patient commitment when added to a PFA, the older the patient, the more likely a TKA will be a more appropriate solution. Radionuclide imaging can be helpful in isolating patellofemoral arthritic activity and pain.54 Tomographic or spectrographic augmentation of such scans has improved accuracy of assessing compartmental sources of pain in our hands (personal observation, WBL). Nuclear bone scan activity is sensitive, but not specific for symptomatic PA.108 More significance can be placed on bone scan activity once transient overuse or acute trauma have been excluded and after patient compliance with a proper patellofemoral specific rehabilitative program. Scans are also useful in identifying complex regional pain syndrome that tends to be present as a more global uptake pattern. A negative scan can help exclude PA in psychogenic presentations or in cases involving secondary gain. MRI is an excellent and widely underutilized choice to reliably provide measurable parameters for extensor malalignment, patella tilt, patella alta/infera, and trochlear dysplasia and depth.99,109 A brief review will equip the surgeon with the basic approach. The most widely accepted radiographic criterion for assessing significant extensor malalignment is to measure the tibial tuberosity-trochlear groove distance.110 The distance between the tibial tubercle location and the center of the trochlear groove can be determined on

155 the axial images using the measurement scale at the bottom of each MRI image. A value of 10-15 mm is considered normal; a distance ⬎ 15-20 mm suggests distal medialization is likely needed.99 Patella height can be measured on the midsagittal view using the true Caton-Deschamps index. This measurement on MRI is the ratio between a line drawn defining the longest length of the actual patellar articular surface (not bony contour) and a line connecting the most distal point on the patellar articular surface to the anterior border of the tibial articular surface on a midsagittal view. Normal value is 0.95-1.0. Patella tilt on MRI should be assessed on axial views at the point where the adductor tubercle is more prominent as this correlates with the attachment site of the medial patellofemoral ligament attachment and the upper portion of the trochlear groove. Patellofemoral dysplasia can also be appreciated in this view (Fig. 4, left knee). Finally, dysplasia of the trochlea can easily be recognized by the method of Pfirrmann et al.109 It is strongly recommended that the reader review the original paper and master these principles.109 The MRI is useful but less sensitive than knee arthroscopy in accurately assessing arthritic extent.112 Used in combination, these tools provide reasonable assurance that a PFA may help the patient’s pain. Because almost all patients with symptomatic patellofemoral degeneration will be offered at least one palliative arthroscopic procedure, disease extent and progression can be reasonably documented.

Salient Points About Operative Technique Surgical PFA technique can be challenging.52 Fortunately, more reliable guide systems and a better understanding of soft balancing of the extensor mechanism have evolved.97 Technical aspects of the operation have been comprehensively described, and the reader is urged to consult these sources for various perspectives.51,52,59,86,99,109,113,115 Principles are similar to all knee arthroplasty. An incision that allows adequate exposure is the correct one. This may vary with the circumstances of the patient. It is often possible, and

Figure 5 Right knee lateral retinacular peel. The retinacular attachment to the lateral patella are released epiperiosteally as described by Shaw.111 (Color version of figure is available online.)

156 in most surgeons’ opinion desirable, to conserve a portion of the vastus medialis obliqus (VMO) attachment. This is important because most of these patients will present with quadriceps muscle dysfunction due to pain inhibition and disuse. Conserving some attachment of the VMO helps to maintain an important dynamic medial force vector on the patella postoperatively. Therefore, in most cases, we have not had to resort to a full paramedian incision. If exposure is compromised, then one can easily extend the vastus release proximally (a medial vastus snip) until lateral translation and/or eversion of the patella is possible. No deliberate attempt is made to imitate a pure minimal incisional approach, but with experience less soft tissue disruption that can retard recovery are easily accomplished.97 In patients who present with a prior Fulkerson type realignment and large lateral incision, we recommend using the same lateral incision to avoid wound healing problems. The deep approach to the joint can then proceed paramedially, but again one should conserve the VMO as much as possible. The surgeon should place the femoral prosthesis in slight external rotation guided by the transepicondylar axis to avoid tightening the lateral retinaculum in flexion as well as to discourage patella subluxation. Any significant preoperative extensor malalignment should be addressed. When the tibial tubercle-trochlear groove distance is ⬎20 mm, an extensor realignment should be considered in addition to PFA ie, tibial tubercle medialization, or medial patellofemoral ligament reconstruction with graft. An attempt at isolated lateral release in these circumstances will usually not suffice. Prepare the patella resection carefully with pre- and post-resection measurement to leave at least 10 mm residual thickness. We prefer an instru-

W.B. Leadbetter and M.A. Mont mented resection rather than free hand. One difference in PFA from TKA technique is not readily apparent. Namely, in flexion medialization of the patella prosthesis will encourage impingement on the medial femoral condyle in knee flexion. The surgeon can place the patella component slightly less medial as long as tracking is not adversely effected. As soft tissue balancing is critical to stability, one of us (WBL) routinely performs a peripatellar or “patellar retinacular peel” as described by Shaw111 (Fig. 5). This technique is useful in both TKA and PFA to avoid a formal lateral patellar release that can further destabilize patella tracking as well as add morbidity. We have found that the lateral patella chamfer cut to be useful to avoid lateral facet osteophytic impingement on the femur and to allow further decompression of the lateral retinaculum as well.53 Prosthetic design has been correlated with surgical success.85,113 At one point, the Lubinus prosthesis accounted for 27.9% of reported PFA failures.21 These failures were linked to the lack of adaptability of the femoral component and led to its abandonment.85,116 Lonner85 has delineated the features of more successful prosthetic design. The Avon prosthesis is typical of the second generation designs that incorporate better sizing, at a more forgiving and less constrained femoral flange for patella capture, and a lower lateral profile with a radius of curvature that better fits the femoral groove.113 (Fig. 6). A design that allows the use of an asymmetric patella component may offer some added resistance to subluxation.99 Onlay designs require less bone resection, although revision of inlay PFA to TKA has not been difficult.58 When severe patellofemoral dysplasia is encountered, a custom prosthesis such as the Kinamed or Performa (Biomet, Warsaw, IN) may be the best choice.117

Outcomes of PFA PFA: General Observations The number of patellofemoral arthroplasties remains low.118 This is not entirely inappropriate, as even with extended indications, the finite number of candidates for PFA is expected be relatively small compared to TKA. In our hospitalbased reconstructive joint practice with emphasis on patellofemoral surgery, PFA constitutes ⬍ 5% of our cases. Surgeons who attempt patellofemoral cartilage restoration can be expected to add to that percentage. Presently, philosophy on PA salvage can be roughly divided into 2 opinions. The first (TKA) emphasizes a more anatomic, arthritis extent, “final solution” based approach. The other approach (PFA) stresses a functional, bridging, less burdensome solution. Most reviewers to date have noted the marked outcome improvement trends of the second generation PFA prosthetic designs.94,118

PFA: Experience in Older Patients

Figure 6 Plain radiograph of Avon (Stryker, Mahwah, NJ, USA) prosthesis (lateral view).

Our most recent review of recent literature on PFA outcomes revealed 19 papers from 1979 to 2009. There were 794 patients with 934 knees. Mean patient age was 55.9 years of age (range, 19-90 years) with a mean follow up of 5.7 years

Patellofemoral arthroplasty

Figure 7 Gait kinematic study 4 months post right knee Avon PFA. Note near exact replication of the normal gait kinematics (operated knee indicated by blue line; green indicates multiple subject normative data pattern) Data from the Wasserman Gait Laboratory, Sinai Hospital, Baltimore. (Color version of figure is available online.)

(range, 0.16-24 years). While outcome measures varied, it was estimated that PFA was successful with a minimum good result in 88% of patients (range, 42%-96%). Higher outcome scores were reported using modern era prosthetic design. However, 3 of the 3 newer PFA designs, the Biomet Vangard (Biomet, Inc, Warsaw, IN), the Natural Knee II (Zimmer, Warsaw, IN), and the Journey PFJ (Smith and Nephew, Memphis, TN) have no outcomes reported in the literature. Outcomes of the Kinematch prosthesis (Kinamed, Camarillo, CA), LCS (DePuy, Warsaw, IN), and the Performa Custom (Biomet, Inc, Warsaw, IN), have been reported, respectively by only a single author.89,117,119 In recent literature, the Avon prosthesis (Stryker, Mahwah, NJ, USA) has the longest documented outcome with the largest number of patients.5,19,20,85,120 Leadbetter et al120 reported on the first multicenter retrospective study using the Avon prosthesis. The series included 70 patients (79 knees) with a mean follow-up of 3 years (range, 2-6 years). There were 66 knees that had KSS greater than 80 points (84%). Seventy-one knees (90%) functioned without pain in daily activity and stair climbing. In our experience, the gait kinematics achieved after PFA can be indistinguishable from that of the asymptomatic contralateral knee (Figs. 7 and 8).

157 in Bristol, England in 1996 and in the United States in 2001. Since that time, the Avon has been widely adopted for its improved design and clinical outcomes.85,113 Leadbetter and Ackroyd122 presented the results of their PFA in 32 patients (42 knees) 45 years old or younger (mean age of 37 years, range 25-45) who had a minimum 2 year follow-up. There were 28 women and 4 men. Using outcome instruments that have been validated for patellofemoral disorders, that is, the Bristol Pain Score, the Bristol Movement score, the Melbourne patellar score, and the Oxford knee score, 90.5% of patients achieved a good to excellent result with 95.6% prosthetic retention. There were no major complications or infections. Postoperative problems included residual pain or mechanical symptoms (9.5%), disease progression (7.1%), persistent maltracking/subluxation (4.7%), patient selection error (eg, excessive preoperation flexion contracture) (2.3%), patellofemoral retinacular pain thought to be due to “overstuffing” (2.3%), and femoral component malrotation (2.3%). Although none of the previously cited reports of TKA for isolated PA mention the specific postoperative recreational activity, these young PFA patients resumed such pursuits as downhill skiing, ballet, cycling, hiking, manual labor, police work, tennis, and aerobic exercise. Although it was stressed to the patients that such activities carry an unknown potential risk to the longevity of their prosthesis and the remaining tibiofemoral compartments, it remained their quality of life choice to engage in these activities.

Novel Applications of PFA PFA can be useful in some difficult clinical situations. Ackroyd et al123 has described salvage of the persistently painful knee with extensor subluxation after patellectomy. In 3 patients the trochlear portion of the Avon prosthesis was used to increase trochlear constraint. Salvage of the failed Fulkerson osteotomy with persistent arthritic pain has been moderately successful in our hands. Of 9 cases, 7 were rated objectively good and 2 were rated

PFA: Experience in Younger Patients The use of PFA in younger patients is not a new development. In the first report of successful PFA in 1979 by Blazina et al,54 the average patients age was 39 years with the youngest recipient of a PFA being 19 years of age. Characteristically, many of these patients had failed multiple operative procedures, particularly patelloplasty. Using a first generation prosthesis (RichardsI/II, Smith and Nephew, Memphis, TN), 78% improved results were attained at 1.8 years (range, 0.7-3.5). The results of the Avon PFA have been reviewed in younger patients.121,122 . This prosthesis was first introduced

Figure 8 Gait kinematic comparative control study. Same patient (unoperated Left knee indicated by red line). (Color version of figure is available online.)

158 fair. The longest follow-up has been in a woman who experienced fracture complications with nonunion of her original osteotomy at the age of 36 years. Despite the presence of patella infera, now aged 45 years, she still functions at a high level and has bilateral PFAs. The youngest such patient presented at 23 years of age with progressive patellofemoral degeneration due to dysplasia and malalignment. She also represented a case of iatragenic chondral injury secondary to thermal patella chondroplasty. Despite multiple strategies including attempts at extensor realignment and tibial tubercle osteotomy, she required bilateral prosthetic salvage. She has had immediate functional improvement at 4 years, with minimal residual symptoms. Interestingly, all PFA patients preferred their PFA recovery to their osteotomy experience. All were off crutch support within 2-3 weeks. Finally, PFA has been used as a combined salvage for both medial unicompartmental arthroplasty124 and with ACI cartilage restoration.125

Conclusions PFA is a compartmental salvage operation that has earned its place for PA treatment by long-established experience and continuing efforts at refinement. PFA has proven to have versatile applications. However, PFA should not be underutilized nor oversold. As our ability to radiologically detect the presence and predict the progression of osteoarthritis and cartilage degeneration improves, so will our success in compartmental salvage of knee arthritis. New developments in MRI hold that promise.126 In younger patients, PFA is a reasonable choice in selected cases to extend function and reduce pain, while avoiding what is undeniably a more complex TKA operation. While the argument has been made that TKA is the procedure of choice in these patients, I would submit that in the hands of the low volume orthopedic surgeon, such treatment is more likely to fail than a PFA.127 PFA is not a panacea and requires its own subset of abilities, not the least of which is conservative judgment and a genuine interest in PFP disorders. Like unicompartmental knee arthroplasty, it remains an intermediate solution for some patients. Because a normal knee will not be attained by any present surgical intervention, PFA remains an important option with lesser risks, reduced recovery burden, and as good or better midterm outcomes than other alternatives.

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