[Pre-operative assessment of the patellofemoral joint in unicompartmental knee replacement using Oxford Phase III and its influence on outcome].

OBJECTIVE: To determine whether anterior knee pain and/or radiological evidences of degeneration of the patellofemoral joint influence the outcome of unicompartmental knee arthroplasty (UKA).

METHODS: Between January 2006 and December 2010, 95 consecutive patients (100 knees) with unicompartmental knee osteoarthritis were treated with Oxford UKA, including 34 males and 61 females. The mean age was 68.2 years (range, 55-82 years). The average Body Mass Index was 26.3 kg/m(2)(range, 24-28 kg/m(2)). Pre-operative there were 43 knees (43.0%) with anterior knee pain and 57 knees (57.0%) without it. Pre-operative radiological status of the patellefemoral joint were defined using Ahlback and Altman systems. The pre- and post-operative results of Oxford Knee Score (OKS), American Knee Society Score (AKS) and Western Ontario and Macmaster (WOMAC) were compared using paired t-test, the results between different groups were compared using grouped t-test.

RESULTS: All cases were followed up for average 50 months (24-84 months). At the last follow-up, none had complications of infection, fat embolism, deep vein thrombosis, malposition of prosthesis, dislocation or loosing. The mean femoral component alignment was -0.7° ± 5.2° (valgus/varus), -0.8° ± 4.5°(flexion/extension); the mean tibial component alignment was -0.1° ± 2.2°(valgus/varus), -0.4° ± 2.4° (flexion/extension). The clinical outcomes were significantly improved compared with pre-operation regardless of presence (OKS: t = 19.04, P < 0.01; AKS knee:t = 38.56, P < 0.01;AKS function:t = 39.29, P < 0.01;WOMAC:t = 43.22, P < 0.01) or absence (OKS: t = 31.57, P < 0.01; AKS knee:t = 40.34, P < 0.01; AKS function:t = 43.62, P < 0.01; WOMAC: t = 47.06, P < 0.01) of anterior knee pain. The results were significantly improved compared with pre-operation (P < 0.01) regardless of whether degeneration of the patellofemoral joint. There was no statistically significant difference in outcome between patients with evidence of degeneration in the medial patellofemoral joint and those without (P > 0.05) . Patients with lateral patellofemoral degeneration had a worse score than those without, OKS (t = 2.56, P = 0.01) and WOMAC (t = 2.20, P = 0.03) by the Altman score, OKS (t = 2.29, P = 0.02) by the Ahlback score. For AKS measures there was no statistically significant difference in outcome (P > 0.05) .

CONCLUSIONS: Neither anterior knee pain nor radiological evidence of medial patellofemoral joint degeneration would influnence the outcome of UKA, lateral patellofemoral joint degeneration have an increased risk of a poor result.