Sex Differences and Impact of Body Mass Index on the Time Course of Knee Range of Motion, Knee Strength, and Gait Speed After Total Knee Arthroplasty

Objective Quadriceps strength deficits and gait speed limitations remain significant issues after total knee arthroplasty (TKA), yet detailed longitudinal data characterizing these measures and their predictors are limited. This study aimed to describe the time course of knee range of motion, quadriceps strength, and gait speed post‐TKA, and to assess whether sex and body mass index (BMI) influenced the time recovery of these measures. Methods A total of 1,025 patients (mean ± SD age 67 ± 8 years) undergoing primary TKA participated. At 4‐, 8‐, 12‐, and 16‐weeks postsurgery, knee range of motion, quadriceps strength, and gait speed were quantified. The associations of the knee and gait measures profile over time with sex and BMI were assessed using generalized least squares modeling. Results The various knee and gait measures improved nonlinearly over time, with substantial improvements observed in the first 8–10 weeks postsurgery. Sex and BMI influenced the time course of quadriceps strength (P < 0.001 for all interactions): improvements in quadriceps strength over time were slower in women and in patients with higher BMI. Post‐TKA gait speed was consistently lower in women than in men, while BMI was negatively and nonlinearly related to gait speed. Conclusion Although the various knee and gait measures improved over time, women and patients with higher BMI had poorer functional outcomes. The present study highlights the need for a mechanistic understanding of the results and targeted management of these patient subgroups.