A Comparative Analysis of Medial Versus Lateral Unicompartmental Arthroplasty: A Case-Matched Analysis of Patient-Reported Outcomes.

Introduction Unicompartmental knee arthroplasty (UKA) is a bone-preserving alternative to total knee arthroplasty (TKA) for isolated compartmental osteoarthritis (OA). The medial compartment is most frequently affected due to varus malalignment, while lateral disease, associated with valgus alignment, is less common. Although UKA offers faster recovery and improved function compared to total knee replacement, direct comparisons between medial and lateral UKA outcomes are limited. This study aims to compare patient-reported outcomes between medial and lateral UKA using a retrospective case-matched design. Methods A retrospective case-matched study was conducted on patients who underwent fixed-bearing UKA performed by a single fellowship-trained surgeon between 2008 and 2023. All procedures followed a standardized surgical and rehabilitation protocol. Lateral UKA cases were matched 1:1 with medial UKA cases for age (±1 year), sex, and follow-up duration (±6 months). The primary outcome was the Forgotten Joint Score-12 (FJS-12) at the latest follow-up. Statistical comparisons used independent t-tests for continuous variables and chi-squared or Fisher's exact tests for categorical data, with significance set at p < 0.05. Effect sizes were quantified using Cohen's d. Results The cohort included equal numbers of medial (n = 25) and lateral (n = 25) UKA cases with no significant differences in demographics. The mean age was 59.3 years, and the mean follow-up was 7.6 years. The mean normalized FJS-12 scores were 56.8 (standard deviation {SD}: 37.7) for medial UKA and 57.4 (SD: 36.0) for lateral UKA (p = 0.86), with a negligible effect size (Cohen's d = 0.05). The item-by-item analysis of the 12 components of the FJS-12 revealed no statistically significant differences between groups across activity-specific domains, including walking, standing, climbing stairs, and sports participation. The graphical distribution of FJS-12 scores showed substantial overlap between the two cohorts. No implant revisions or major complications were recorded in either group. Conclusion In this case-matched analysis of medial and lateral UKA performed by a single surgeon, patient-reported outcomes were equivalent at mid-term follow-up. Both medial and lateral UKA demonstrated comparable joint "forgettability" and functional integration, with no revisions observed. These findings indicate that, when performed with appropriate patient selection and consistent surgical technique, lateral UKA can achieve outcomes equivalent to medial UKA. The results support the safe and effective use of lateral UKA as a viable option for isolated lateral compartment disease.