Impact of high body mass index on functionally aligned image-based robotic total knee arthroplasty: Comparable functional outcomes but higher mechanical failures

Abstract

Objectives

Increased body mass index (BMI) poses challenges in total knee arthroplasty (TKA), including higher complication rates. Functional knee positioning (FKP) with robotic assistance provides a personalized approach to optimize alignment and soft-tissue balance, but its impact on patients with increased BMI remains unclear. This retrospective comparative study aims to evaluate the influence of obesity and its severity on clinical outcomes and complications in TKA performed with an image-based robotic system-guided by FKP principles.

Methods

This retrospective comparative study included 372 patients who underwent robotic-assisted TKA following FKP principles. Patients were stratified into two main groups based on BMI (<30 ​kg/m²; 238 patients and ≥30 ​kg/m²; 134 patients). Outcomes included Knee Society Scores (KSS), Forgotten Joint Scores (FJS), range of motion (ROM), implant positioning, and complications, evaluated at a minimum follow-up of two years.

Results

Patients with increased BMI (≥30 ​kg/m²) demonstrated similar functional outcomes to patients with BMI <30 ​kg/m² in terms of ROM, KSS, and FJS. However, the revision rate due to mechanical failures was significantly higher in the obese group (2.99% vs. 0.42%, p ​= ​0.04; hazard ratio ​= ​6.8; 95% CI, 1.09–42.31). Implant positioning was consistent across groups, except for reduced femoral external rotation in the increased BMI group (p ​= ​0.004).

Conclusions

Robotic-assisted TKA with FKP principles achieves comparable functional outcomes for obese patients at a minimum of a 2-year follow-up, demonstrating the system's ability to address anatomical and functional challenges. However, obesity remains a critical risk factor for mechanical failures.

Level of evidence

III.