Mid-term clinical outcomes of mobile-bearing UKA: a retrospective study on the influence of patellofemoral joint disease, lower limb alignment, and implant positioning

BACKGROUND: Unicompartmental knee arthroplasty (UKA) has become an effective treatment for medial compartment osteoarthritis of the knee. However, its use in patients who also have patellofemoral joint osteoarthritis (PFOA) before surgery remains controversial. Restoring postoperative lower limb alignment and achieving accurate implant positioning are also important factors for the success of UKA, but there is still a lack of studies that combine both patient-related factors and surgical technique-related factors in the Chinese population. METHODS: This study retrospectively analyzed 69 Chinese patients (79 knees) with medial compartment osteoarthritis who underwent Oxford UKA between May 2017 and December 2020. The severity and location of PFOA were assessed by MRI. Postoperative coronal alignment was categorized by the femorotibial angle (FTA) into neutral, mild varus, moderate varus, and extreme/out-of-range groups. Implant positioning was classified as ideal or non-ideal according to established radiographic target ranges for aLDFA, aMPTA, PTS, and component alignment angles. Functional outcomes were evaluated using VAS, KSS, WOMAC, and Kujala scores, with multifactorial interactions analyzed via multivariate analysis of covariance (MANCOVA). RESULTS: At a mean follow-up of 66.5 ± 9.6 months, Oxford UKA markedly improved overall patient function. While no cases of prosthesis loosening or revision were observed, three patients reported persistent postoperative pain and two presented with valgus deformity. Postoperative functional scores did not differ by PFOA severity or lesion location. Regarding lower-limb alignment, neutral and mild varus (< 6°) knees had higher KSS function scores than moderate varus and extreme/out-of-range knees and lower WOMAC scores. KSS knee scores were higher in neutral and mild varus than in the extreme group. Implant positioning (ideal vs non-ideal) was not associated with postoperative scores. CONCLUSION: Mid-term follow-up showed that Oxford UKA achieved satisfactory clinical outcomes. The severity and location of PFOA before surgery did not significantly affect postoperative knee function. Maintaining postoperative alignment within the target range (neutral to slight varus; within 6° of varus) may be associated with better functional recovery.