Obesity Is Associated With Earlier Mechanical Failure Following Total Ankle Arthroplasty Independent of Tibial Stem or Keel Augmentation

Abstract

Background: Obesity and elevated body mass have been associated with increased rates of aseptic loosening and implant failure following total ankle arthroplasty (TAA). The purpose of this study was to investigate the role for primary stemmed or keeled tibial implants as a protective factor against aseptic loosening in this patient population. Methods: We performed a retrospective cohort study of 699 modern primary TAAs with a minimum 2-year follow-up performed at a large academic institution between 2010 and 2023. Patients were stratified by body mass index (BMI <30 vs ≥30) and implant design (stem/keel vs low-profile). The primary outcome was mechanical failure requiring revision of metal components. Secondary outcomes included patient-reported outcomes (FAAM-ADL and VAS). Kaplan-Meier analysis and multivariable cox proportional hazards were used to assess revision risk. Results: Of 699 primary TAAs, 39 (5.6%) experienced mechanical failure at a mean follow-up of 5.6 years. After adjustment for age, implant type, and subtalar fusion, BMI ≥30 was associated with a greater than 2-fold increased hazard of mechanical failure (HR 2.27, 95% CI 1.07-4.81, P = .033). Kaplan-Meier survivorship was similar for low-profile (93.7%) and stem/keel (96.1%) implants at 5 years. When stratified by both BMI and implant type, with the numbers available, no significant difference could be detected in mechanical failure, time to revision, or patient-reported outcomes were observed ( P > .05). Obese patients had worse preoperative FAAM-ADL and VAS scores but achieved comparable postoperative outcomes. Conclusion: After adjusting for age, implant design, and subtalar fusion, BMI ≥30 was independently associated with a significantly higher hazard of mechanical failure and shorter time to revision. Despite the proposed biomechanical advantages of increased tibial fixation, the stemmed or keeled implants used in this cohort were not associated with improved survivorship or patient-reported outcomes at mid-term follow-up. Level of Evidence: Level III, retrospective cohort study.