To compare the difference of clinical outcomes after unicompartmental knee arthroplasty(UKA) between medial compartmental osteoarthrispatients with and without bonemarrow edema (BME) in the patella and to evaluate the effect of patellofemoral osteoarthritis (PFOA) on postoperative functionafter UKA.

A total of 141patients (146knees) undergone medial UKA were selected in Shanghai Tenth Hospital. Inclusion criteria: intact anterior cruciate ligament; varus deformity within 15° which can be corrected under valgus stress; flexion contracture within 15° and flexion over 90°. Exclusion criteria: previous fracture or operation history of lower limb on the operative side; postoperative complications; inflammatory osteoarthritis; anterior cruciate ligament injury. According to the Kellgren-Lawrence (K-L) scale and bonemarrow edema (BMEP) pattern grade of patellofemoral joints, patients were divided into three groups: Group A, non-PFOA (K-L=0); group B, PFOA without BME (K-L≥1, BMEP=0); group C, PFOA with BME (K-L≥1, BMEP≥1). The visual analog scale (VAS) scores, Hospital for Special Surgery (HSS) scores, and range of motions (ROMs)were used to assess the clinical outcomes atthe postoperative follow-up of three months and two years. The data comparison was performed with the analysis of variance, LSD test and chi-square test.

BME was highly correlated to poor outcome in patients with UKA. At follow-up of three months, group A was worse than the others in terms of knee pain VAS scores and active ROMs(F=30.767, 92.269, P<0.05). At follow-up of two years, the anterior knee painVAS scores and active ROMs were still worse thanthat of patients without BME(F=3.268, 10.220, P<0.05).

Clinical outcomes in patients without BME are no difference whether combining PF OA or not. The condition of BME in the patella should be taken serious consideration due to the adverse effect on theoutcome after UKA.