To investigate the effect of patellofemoral osteoarthritis (PF-OA) on the knee functions aftermedialunicompartmental knee arthroplasty (UKA) for medial knee osteoarthritis on the Oxford active platform.

Seventy patients underwent UKA at the Luoyang Orthopedic-Traumatological Hospital (Orthopaedic Hospital of Henan Province) between May 2017 to April 2019 were retrospectively analyzed. Based on the Ahlback classification of patellofemoral degeneration, the patients were divided into the no patellofemoral degeneration group (non PF-OA group, 25 patients), the medial patellofemoral degeneration group (medial PF-OA group, 28 patients) and the lateral patellofemoral degeneration group (lateral PF-OA group, 17 patients). visual analogue scale (VAS), Oxford knee joint score (OKS) and hospital for special surgery knee score (HSS) were used to evaluate the pain and function of knee joint before and after operation. The VAS, OKS and HSS scores were compared between groups at the same time point using one-way ANOVA, and the LSD test was used for two-way comparisons between groups where the variance was the same, and the Game-Howell test was used for those data variance were not the same.

Compared to the preoperative period, the patients in the non PF-OA, medial PF-OA and lateral PF-OA groups at the final follow-up had significantly lower VAS scores (t=27.26, 31.80, 20.88, all P<0.05); lower OKS scores (t=-27.11, -28.43, -15.04, all P<0.05); HSS scores were also improved (t=-17.66, 11.08, 10.06, all P<0.05). At the end of follow-up, the differences in VAS scores and OKS scores among the three groups were not statistically significant (all P>0.05) and the differences in HSS scores among the three groups were statistically significant (Fw=10.28, P<0.01). HSS scores in the lateral PF-OA group were lower than those in the medial PF-OA group (ω²=0.36 P<0.01) and the non PF-OA group (ω²=0.30, P<0.01) at the last follow-up, and the difference was statistically significant (P<0.05); HSS scores difference between the medial PF-OA and non PF-OA groups was not statistically significant (P>0.05).

Degeneration of medial patellofemoral joint does not affect the clinical outcomes of UKA for medial knee osteoarthritis, and should not be regarded as a contraindication for UKA. Although the degeneration of lateral patellofemoral joint may have a negative effect on the clinical outcomes of UKA, the knee function after the operation is still markedly improved. UKA can still be performed in the specific population with lateral patellofemoral joint degeneration of AhlbackⅡ and Ⅲ grade.