A 21 % conversion rate to total knee arthroplasty of a first-generation patellofemoral prosthesis at a mean follow-up of 9.7 years

Purpose: To evaluate the mid- to long-term results of the Richards’ type II patellofemoral arthroplasty (PFA) in terms of functional scores, number and type of complications, patient satisfaction and survival. Methods: We retrospectively studied patients that received a Richards’ type II PFA at our institution between 1998 and 2007. Patients with a functioning PFA at the time of this study were evaluated. Outcomes included survival rates with endpoint loss of prosthesis, number and type of complications, Knee Society Scores (KSS) and Visual Analogue Scale (VAS) for pain. In addition, patients were asked how surgery influenced their original symptoms. Results: Twenty-four patients (33 prostheses) were included. Follow-up ranged from 2.2 to 18.8 years with a mean of 9.7 years. Survival at 10 years was 73 % (95 % CI, 57–93 %). Median KSS score was 163 (range, 110–200). Median VAS Pain was 30 (range, 0–80) and VAS Satisfaction median was 90 (range, 50–100). Thirteen (62 %) PFAs were rated excellent, six (28 %) as good and two (10 %) as fair. Twelve (36 %) of the cases required further surgery within 4 years after implantation. Seven of these (21 %) were converted to TKA after a mean time of 5.5 years, five out of seven were converted because of ongoing tibiofemoral osteoarthritis (TFOA). Conclusions: We found a rate of 21 % (7/33) conversion of the Richards’ II PFA to TKA after a mean of 5.5 years; 71 % (5/7) of cases were because of TFOA. We strongly advise not to use PFA if there is any sign of joint disease in other compartments than patellofemoral.