The Influence of Obesity on Unicondylar Knee Arthroplasty.

INTRODUCTION: Some prior studies suggest obesity increases unicondylar knee arthroplasty (UKA) failure risk. This study evaluated obesity's impact on UKA outcomes at a single institution. METHODS: We analyzed 4,973 primary cemented medial UKAs performed by eight surgeons from 2000 to 2022. The primary outcome was implant survivorship. Secondary outcomes included revision rates, reasons for revision, patient-reported outcomes, and clinical metrics. The mean age was 66 years (range, 33 to 96), 54.6% were women, body mass index (BMI) averaged 29.9 (range, 15.6 to 63.4), and follow-up averaged 5.1 years. Outcomes were stratified by BMI cutoffs (BMI: 30; 35; 40), yielding group sizes of ≤ 30 (N = 2,858), > 30 (N = 2,115), ≤ 35 (N = 4,137), > 35 (N = 836), ≤ 40 (N = 4,680), and > 40 (N = 293). RESULTS: At five and 10-years, implant survivorship was 95.7 and 92.8%, respectively. At five years, survivorship remained high but declined slightly with increased BMI for the 30 and 35 cutoffs (≤ 30: 96.7%, > 30: 94.2%, P < 0.001; ≤ 35: 95.8%, > 35: 94.9%; P = 0.005), while a slight, non-significant increase occurred for BMI > 40 (≤ 40: 95.7%, > 40: 96.0%; P = 0.325). Arthritis progression was the most common revision reason, increasing with BMI. Infection rates remained low across all BMI's. There was no difference in the percentage of patients achieving a minimal clinically important difference using the Knee Osteoarthritis Outcome Score, Joint Replacement (KOOS, JR) with each BMI cutoff, but KOOS, JR score changes were significantly greater in the higher BMI patients using the BMI 30 cutoff (P = 0.034). CONCLUSIONS: While higher BMI patients had marginally higher rates of revision, we remain enthusiastic about UKA in these patients due to low infection rates across all BMI cohorts and improvements in PROMs.