Conversion of patellofemoral arthroplasty to total knee arthroplasty

Background and purpose The long-term outcome of patellofemoral arthroplasty is related to progression of femorotibial osteoarthritis with need for conversion to total knee arthroplasty. We investigated whether prior patellofemoral arthroplasty compromises the results of total knee arthroplasty. Methods 13 patients who had had 14 Richards type II patellofemoral arthroplasties converted to total knee arthroplasty because of femorotibial osteoarthritis, were individually matched to a control group of 13 patients with 14 primary total knee arthroplasties. The mean follow-up times for the patients and the control group were 5.7 (2-13) years and 5.2 (2-13) years, respectively. Clinical outcome was assessed using Knee Society score (KSS), WOMAC score, range of motion, and complications. Results KSS and WOMAC scores were similar in the two groups (KSS in patient and control groups: 82 and 86 (p = 0.6); KSS function: 76 and 88 (p = 0.5); WOMAC score: 33 and 21 (p = 0.1)). Within 6 months after conversion, 3 knees had to be manipulated under anesthesia for limited motion. No patients in the control group required manipulation under anesthesia. Interpretation Patellofemoral arthroplasty appears not to have a negative effect on the outcome of later total knee arthroplasty.