Functional scores and prosthetic implant placement are different for navigated medial UKA left in varus alignment

PURPOSE: The purpose of this study was to analyze the clinical outcomes and radiologic position of the knee in two groups of patients after medial unicompartmental knee arthroplasty (UKA): one group with residual varus axis (RVA) alignment and other one with neutral mechanical axis (NMA) of the lower limb. METHODS: All patients who underwent UKA between January 2015 and January 2018 were evaluated retrospectively. Inclusion criteria were: medial UKA for isolated medial femoro-tibial osteoarthritis, a varus deformity of < 15°, and a minimal follow-up of 2 years. All patients had a preoperative and postoperative clinical examination with functional scores (New International Knee Score (NewIKS) and Knee injury and Osteoarthritis Outcome Score (KOOS) and radiographs. Preoperative and postoperative values for continuous outcomes were compared using the Student's t test for paired data and differences between the groups were compared with the Mann-Whitney U test. p < 0.05 was considered statistically significant. RESULTS: The RVA group consisted of 48 cases of medial UKA in 48 patients (22 females). Mean postoperative hip-knee-ankle (HKA) angle was 174.3° ± 2.8 and the corresponding mean AKI angle (tibial mechanical angle) was 82.9° ± 2.9. The NMA group consisted of 35 cases of medial UKA in 35 patients (14 females). Mean postoperative HKA angle was 178.9° ± 3 and the corresponding mean AKI angle was 85.5° ± 3.1. A significant difference was found between the two groups for the KOOS score and for global NewIKS, with a better score in the RVA group. CONCLUSIONS: RVA alignment after medial UKA results in a significant improvement in functional knee scores at 2-year post-surgery. Return to sport and recreational activities was better than in patients with postoperative NMA. LEVEL OF EVIDENCE: Level 3; retrospective cohort study.