ASSOCIATED PATELLOFEMORAL OSTEOARTHRITIS IS NOT A CONTRAINDICATION FOR UNICOMPARTMENTAL KNEE REPLACEMENT. REPORT OF 110 PROSTHESES WITH AN AVERAGE 6-YEAR FOLLOW-UP.

INTRODUCTION: Associated patellofemoral joint osteoarthritis (APFJ-OA) has typically been considered a contraindication for unicompartmental knee arthroplasty (UKA) in the treatment of femorotibial joint osteoarthritis. However, this contraindication is being challenged. The aim of this study was to assess clinical and functional outcomes, complications, and implant survival in medial or lateral UKA, regardless of clinical symptoms or radiographic signs of APFJ-OA.

METHODS: This retrospective, comparative study included patients treated with medial or lateral UKA regardless of preoperative symptoms or signs of APFJ-OA, with a minimum 2-year follow-up. Intraoperatively, knees were subdivided based on APFJ-OA grade, according to the Outerbridge classification. Clinical and functional outcomes were analyzed using the 2011 Knee Society Score (KSS) at the last follow-up control. APFJ-OA was treated systematically, in a tailored, stepwise fashion according to its severity. Complication and implant survival rates were evaluated. Two-sided paired T-test, ANOVA and Kruskal-Wallis tests were used with a significance level of 5%.

RESULTS: Finally, 110 UKAs were assessed, 81 (73.6%) medial and 29 (26.4%) laterals. Average follow-up was 6 years (2-19.5). According to Outerbridge, 22 knees (20%) were grade 2, 59 (53.6%) grade 3 and 29 (26.4%) grade 4. All 3 groups showed a statistically significant increase in KSS scores and range of motion. There were no significant differences in clinical KSS improvement and flexion contracture between Outerbridge groups (average 35.7 and -4.9 respectively). Group 3 showed statistically significant improvement in functional KSS when compared to group 2 (68.8 vs 61.2). In maximum flexion, groups 3 and 4 did significantly better than group 2 (20º vs 15º). Three prostheses (2.7%) needed revision after 7, 8.6 and 12 years due to aseptic tibial loosening. Implant survival was 100% at 5 (64 of 64), 97% at 7 (30 of 31), 93% at 9 (14 of 15) and 89% at 12 years, respectively (8 of 9).

CONCLUSION: Clinical and functional results, complications and survival of medial or lateral UKA were not negatively affected by APFJ-OA assessed intraoperatively using Outerbridge classification after an average follow-up of 6 years. We consider that APFJ-OA is not a contraindication for UKA when treated systematically according to its severity.

LEVEL OF EVIDENCE: IV.