Patellofemoral arthroplasty.

Isolated patellofemoral arthritis can occur in as many as 9% of patients older than 40 years and is particularly common in women, who often have subtle patellofemoral maltracking or malalignment. In fact, 24% of women with symptomatic knee arthritis have localized patellofemoral arthritis. Arthroplasty options can provide predictable pain relief, whereas other surgical measures for refractory patellofemoral arthritis--arthroscopic debridement, cartilage grafting, patellectomy, tibial tubercle unloading procedures--often have unsatisfactory results. While total knee arthroplasty (TKA) yields excellent results in >90% of patients with isolated patellofemoral arthritis, it is not desirable in patients who are young and active. Therefore, patellofemoral arthroplasty has a legitimate role in the treatment of isolated anterior compartment arthritis. Early patellofemoral implants were plagued by a high incidence of patellar maltracking, catching and subluxation, due to design features of the trochlear components, inadequate soft tissue balancing, and component malposition. Most importantly, contemporary onlay style trochlear components, implanted perpendicular to the anteroposterior axis of the femur, have substantially reduced the patellar maltracking that was so prevalent with inlay style prostheses for 3 decades. With onlay trochlear designs, early patella instability problems have been reduced, leaving late tibiofemoral degeneration as the primary cause of failure of patellofemoral arthroplasties. Several long-term studies have shown a rate of tibiofemoral degeneration of approximately 20% at 15 years. Finally, the results of TKA do not seem to be compromised by the presence of a prior patellofemoral arthroplasty.