No influence of obesity on survival of cementless, posterior-stabilised, rotating-platform implants

This study compares survival and outcomes in four total knee arthroplasty (TKA) populations defined by baseline body mass index (BMI). We hypothesised that there would be no difference in survival between the groups.

Using an initial cohort of 1059 TKAs, BMI was systematically measured prior to surgery. A retrospective study was conducted and patients were accordingly allocated to four groups: normal or underweight (BMI < 25; n = 111), overweight (25 ≤ BMI < 30; n = 417), moderately obese (30 ≤ BMI < 35; n = 330) and severely or morbidly obese (BMI ≥ 35; n = 201). The pre- and postoperative clinical and radiographical profiles of the four groups were compared, along with any postoperative complications and the survival of each group. The minimum follow-up was 24 months. All implants had an ultra-congruent cementless posterior-stabilised rotating-platform design (Amplitude^®). The primary endpoint was implant survival using Kaplan-Meier analysis. Statistical analysis was conducted using Chi-squared and Kruskal-Wallis H tests to compare the data with p < 0.05.

A total of 94 knees from normal weight or underweight individuals were analysed, 346 from overweight, 281 from moderately obese and 159 from severely or morbidly obese. All knees had been operated on between 2002 and 2011 with an average follow-up of 61.7 (12-146) months. A greater degree of obesity was significantly correlated with young age at intervention (p < 0.001), as well as with a low average preoperative maximum flexion angle (p < 0.001) and KSS (p < 0.001). Postoperatively, there were no significant differences between the groups in terms of patient satisfaction (p = 0.9) or mechanical axial deviation evaluated with whole-leg standing radiography (mFTA, p = 0.3; mFA, p = 0.1; mTA, p = 0.3). The greater the degree of obesity, the lower the average postoperative maximum flexion angle (p < 0.001), KSS knee score (p < 0.001) and function score (p = 0.005). There was no significant difference between the groups in terms of total rate of postoperative complications (p = 0.9) or implant revision (p = 0.9), or in terms of 10-year implant survival (p = 0.4).

Obesity does not affect mid-term implant survival, irrespective of BMI, but has a negative influence on functional outcomes and potential risk of postoperative complications.