Total knee arthroplasty in patients with severe obesity: outcomes of standard keeled tibial components versus stemmed universal base plates

BACKGROUND: Patients with severe obesity [body mass index (BMI) ≥ 40 kg/m(2)] potentially overload the tibial component after total knee arthroplasty (TKA), risking tibial subsidence. Using a cemented single-radius cruciate-retaining TKA design, this study compared the outcomes of two tibial baseplate geometries in patients with BMI ≥ 40 kg/m(2): standard keeled (SK) or universal base plate (UBP), which incorporates a stem. METHODS: This was a retrospective, single-centre cohort study with minimum 2 years follow-up of 111 TKA patients with BMI ≥ 40 kg/m(2): mean age 62.2 ± 8.0 (44–87) years, mean BMI 44.3 ± 4.6 (40–65.7) kg/m(2) and 82 (73.9%) females. Perioperative complications, reoperations, alignment and patient-reported outcomes (PROMS): EQ-5D, Oxford Knee Score (OKS), Visual Analogue Scale (VAS) pain score and satisfaction were collected preoperatively, and at 1 year and final follow-up postoperatively. RESULTS: Mean follow-up was 4.9 years. SK tibial baseplates were performed in 57 and UBP in 54. There were no significant differences in baseline patient characteristics, post-operative alignment, post-operative PROMs, reoperations or revisions between the groups. Three early failures requiring revision occurred: two septic failures in the UBP group and one early tibial loosening in the SK group. Five-year Kaplan–Meier survival for the endpoint mechanical tibial failure was SK 98.1 [94.4–100 95% confidence interval (CI)] and UBP 100% (p = 0.391). Overall varus alignment of the limb (p = 0.005) or the tibial component (p = 0.031) was significantly associated with revision and return to theatre. CONCLUSIONS: At early to mid-term follow-up, no significant differences in outcomes were found between standard and UBP tibial components in patients with BMI ≥ 40 kg/m(2). Varus alignment of either tibial component or the limb was associated with revision and return to theatre.