Mid-Term Evaluation of the Unicompartmental Knee Arthroplasty in Patients with BMI of 40 or Greater

Limited evidence is available on mid-term follow-up for patients with body mass index (BMI)>= 40 receiving a unicompartmental knee arthroplasty (UKA). The primary objective of this study was to investigate survival of the UKA in patients with BMI >= 40. Secondary objectives were to assess functional and patient reported outcome measures (PROMs). Survival analysis with endpoint revision of any component for any reason was conducted using Kaplan-Meier technique on 121 knees (103 patients) that underwent UKA with Oxford Phase 3 implant (Oxford Knee, Biomet, Swindon, United Kingdom) between September 2001 and March 2014 by seven surgeons. Survivorship differences were compared using Log Rank (Mantel-Cox) tests, and Cox Proportional Hazard Model was used to assess predictors of failure. Preoperative PROMs were compared at 2 and 5 years postoperatively using paired t -tests. Mean age of patients was 58 years (43-75), mean BMI 43kg/m (2) (40-51), and mean follow-up 7 years (2 months to 15 years). Survival rate for the whole cohort was 92% at 2 years and 86% at 5 years. Females had a significantly higher revision rate than males ( p =0.043). A total of 19 knees required revision (16 to TKA, 2 polyethylene liner exchanges, and 1 femoral component and liner revision). With respect to PROMs, there was a significant improvement at 2 and 5 years ( p <0.001) on 4 of 5 knee injury and osteoarthritis outcome score subscales. The mid-term survival rate for the Oxford UKA in patients with morbid obesity is similar to that of other nondesigner patient series with BMI<greater than or equal to>30, which provides further evidence for the safety of the implant in this patient population with significant improvements on PROMs at short and mid-term follow-up.