Different optimal alignment but equivalent functional outcomes in medial and lateral unicompartmental knee arthroplasty

Introduction Several differences in kinematics, functional outcomes and alignment exist between medial and lateral unicompartmental knee arthroplasty (UKA). Therefore, the purpose of this study was (1) to compare functional outcomes between both procedures with the hypothesis that both have equivalent outcomes and (2) to assess the role of preoperative and postoperative alignment on functional outcomes in both procedures. Methods Patients who underwent UKA were included when overall function — using Western Ontario and McMaster Universities Arthritis (WOMAC) score – and joint awareness – using Forgotten Joint Score (FJS) — were available preoperatively and at minimum two-year follow-up. A total of 143 medial UKA and 36 lateral UKA patients reported outcomes at mean 2.4-years follow-up (range 2.0 to 5.0year). Results Preoperatively and postoperatively, no differences were seen between medial and lateral UKA in overall function (89.8±11.7 vs. 90.2±12.4, respectively, p =0.855) and joint awareness (71.2±24.5 vs. 70.9±28.2, respectively, p =0.956). With neutral postoperative alignment (−1° to three degrees), less joint awareness was noted following medial UKA than lateral UKA (72.6±22.6 vs. 55.3±28.5, p=0.024). With undercorrection (three degrees to seven degrees), however, following lateral UKA less joint awareness (85.3±19.5 vs. 68.2±26.8, p=0.020) and better functional outcomes (96.0±5.4 vs. 88.5±11.6, p=0.001) were noted than medial UKA. Conclusion Equivalent functional outcomes were noted between medial and lateral UKA at short-term follow-up but different optimal alignment angles seem to exist for both procedures. Level of evidence Level III therapeutic study.