Unicompartmental Knee Arthritis: Patellofemoral Arthroplasty

David Backstein M.D., MEd, FRCSC
Toronto, ON

It is now recognized that isolated patellofemoral (PF) arthritis is a clinical entity of significant frequency, which is considerably disabling to those who suffer from it. Davies et al1 found a 9% (19/206 knees) prevalence of isolated PF arthritis in 174 consecutive patients over 40 years old and 13.6% in women over 60 years old. In a radiographic study of 273 symptomatic knees in women, McAlindon2 found an 8% prevalence of isolated PF arthritis. These data clearly indicate that this condition is worthy of some attention.

When symptomatic PF arthritis becomes recalcitrant to nonoperative management, surgical options other than patellofemoral arthroplasty have traditionally included: 1) arthroscopic debridement, 2) unloading anteromedial transfer of the tibial tubercle, 3) patellectomy and 4) cartilage grafting techniques. Total knee arthroplasty is also a viable option. However; in a young patient with isolated PF arthritis, it may be considered overly aggressive. Furthermore, residual anterior knee pain has been reported in 7-19% of TKAs done for isolated PF arthritis3,4,5.

Figure 1: Preoperative skyline view of isolate osteoarthritis patellofemoral joint OA.











Design Issues

PF arthroplasty has been a controversial treatment alternative. Implantation of early devices such as the Mckeever prosthesis had less than ideal outcomes due to their metal-on-cartilage articulation. Later, inadequate design features of the femoral component including the radius of curvature, inadequate proximal extension of the anterior flange, medial lateral breadth and the degree of constraint lead to catching, snapping, pain and general dissatisfaction. In addition, poor instrumentation made implantation challenging and component position somewhat unpredictable.


Figure 2: Postoperative patellofemoral arthroplasty AP view of the knee.

















In my opinion, however, newer designs and improved instrumentation now make PF arthroplasty a potential option for patients with isolated PF arthritis and pain of patellofemoral origin, after failure of nonoperative measures. Pain, which is patellofemoral in origin, is generally localized anteriorly in the knee or immediately adjacent to the patella. Symptoms are exacerbated by climbing stairs, squatting, prolonged sitting with the knee flexed or getting up from a chair. Candidates for PF arthroplasty should have tenderness on palpation of the involved facet, signs of patellar apprehension and patellar crepitus. There should be an absence of medial or lateral joint line tenderness that is indicative of medial or lateral tibio-femoral compartment degenerative disease. Contraindications to PF arthroplasty include inflammatory arthritis, chondroalcinoisis and significant patellar maltracking or malalignment. Mild patellar tilt is not considered a contraindication, although it may indicate the need for lateral release at the time of PF arthroplasty. Patients with high Q angles may require anteromedialization of the tibial tubercle prior to PF arthroplasty to insure proper tracking.

Preoperative radiographic evaluation should include standing anteroposterior and midflexion posteroanterior radiographs to assist in ruling out the presence of tibiofemoral arthritis. Lateral X-rays will reveal the presence of patellofemoral osteophytes, patella alta or baja. Skyline views may display the presence of patellar tilt and loss of patellofemoral joint space. However, it is not uncommon for the patellofemoral joint space to appear well preserved, with subchondral sclerosis and facet "flattening" as the only radiographic clues. When in doubt about the diagnosis, I have used MRI to further assess the chondral surface of the patellofemoral as well as tibio-femoral joints. Frequently, these patients have had prior arthroscopic debridement and descriptions or photos of the joint condition are available.

Figure 3: Postoperative patellofemoral arthroplasty lateral view of the knee.















The surgical technique is not complex but has been prone to technical error in the past due to poor instrumentation. A short midline incision is used which can be readily utilized for future TKA. An anterior femur cut is made flush with anterior cortex, parallel to the trans-epicondylar axis and perpendicular to the AP axis. The intercondylar area is contoured to fit the femoral component and the patella is resurfaced in the same manner as a standard TKA. In the past, much of the femoral contouring was performed free-hand; however, new systems provide for milling techniques through guides.

Several recent reports of PF arthroplasty results have been encouraging. Ackroyd6 reviewed 109 knees and found 80% good or excellent results at an average of five years follow-up. Development of OA in other compartments was the reason for 28% of failures. Merchant7 found good or excellent results in 94% of 16 knees at an average follow-up of 4.5 years. Kooijiman and Lonner reported good outcomes with 86% and 96% of patients having good or excellent results respectively8,9.

In a small series, Lonner examined conversion of PF arthroplasty to TKA and found no compromise of TKA outcomes. There was no need for stems, augments or bone grafts. Knee society scores improved significantly (57 to 96 clinical and 51 to 91 function) at an average of 3.1 years follow-up10.

Figure 4: Postoperative patellofemoral arthroplasty skyline view of the knee.












In my opinion, young patients (<55 years old) with a diagnosis of isolated patellofemoral OA based on symptoms and imaging, without tibiofemoral changes, are good candidates for PF arthroplasty once nonoperative measures have been exhausted. Elderly patients with debilitating patellofemoral OA are probably better managed with TKA due to the highly predictable nature of outcomes and since some degree of tibiofemoral chondral change is likely to be present.


  1. Davies A.P., Vince A.S., Shepstone L., Donell S.T., Glasgow M.M. The radiologic prevalence of patellofemoral osteoarthritis. Clin Orthop Relat Res. 2002; (402):206-12.
  2. McAlindon T.E., Snow S., Cooper C., Dieppe P.A. Radiographic patterns of osteoarthritis of the knee joint in the community: the importance of the patellofemoral joint. Ann Rheum Dis. 1992;51:844-9.
  3. Laskin R.S. van Steijn M. Total knee replacement for patients with patellofemoral arthritis. Clin Orthop Relat Res. 1999 Oct;(367):89-95.
  4. Mont M.A., Haas S., Mullick T., Hungerford D.S. Total knee arthroplasty for patellofemoral arthritis. J Bone Joint Surg Am. 2002 Nov;84-A(11):1977-81.
  5. Parvizi J., Stuart M.J., Pagnano M.W., Hanssen A.D. Total knee arthroplasty in patients with isolated patellofemoral arthritis. Clin Orthop Relat Res. 2001 Nov;(392):147-52.
  6. Ackroyd C.E., Newman J.H., Evans R., Eldridge J.D., Joslin C.C. The Avon patellofemoral arthroplasty: five-year survivorship and functional results. J Bone Joint Surg Br. 2007 Mar;89(3):310-5.
  7. Merchant A.C. Early results with a total patellofemoral joint replacement arthroplasty prosthesis. J Arthroplasty. 2004;19:829-36.
  8. Kooijman H.J., Driessen A.P., van Horn J.R. Long-term results of patellofemoral arthroplasty. A report of 56 arthroplasties with 17 years of follow-up. J Bone Joint Surg Br. 2003;85:836-40.
  9. Lonner J.H. Patellofemoral arthroplasty: pros, cons, and design considerations. Clin Orthop Relat Res. 2004 Nov;(428):158-65
  10. Lonner J.H., Jasko J.G., Booth RE Jr.. Revision of a failed patellofemoral arthroplasty to a total knee arthroplasty. J Bone Joint Surg Am. 2006 Nov;88(11):2337-42.

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