Influence of body mass index on sagittal hip range of motion and gait speed recovery six months after total hip arthroplasty

Purpose In practice, obesity leads to poor functional outcomes after total hip arthroplasty (THA). However, in clinical research, the influence of body mass index (BMI) on the gait recovery and kinematics for THA is not well documented. The purpose of this study was to assess the influence of BMI on gait parameters pre-operatively and six months after THA for hip osteoarthritis (OA) patients. Methods We included 76 THA for hip OA: non-obese group (G1): 49 (BMI < 30 kg/(2)) and obese group (G2): 37 (BMI >= 30 kg/m(2)) with a control group of 61 healthy people. Clinical evaluation (HOOS) and a 3D gait analysis (gait speed and flexion range of the hip (ROM)) were performed before and six months after THA: The gains between the two visits were calculated and we looked for correlations between outcomes and BMI. Results Preoperative gait speed and hip ROM were significantly lower in obese patients (speed G1: 0.81 +/- 0.22 m/s vs. G2: 0.64 +/- 0.23 m/s, p = 0.004 and hip ROM G1: 26.1 degrees +/- 7.3 vs. G2: 21.4 degrees +/- 6.6, p = 0.005), and obese patients were more symptomatic. At six months, gait speed and hip ROM were significantly lower for all patients compared with the control group. No correlation between gait velocity, hip ROM, and BMI was found. Biomechanical and clinical gains were comparable in the two groups. Conclusions All patients, including obese patients, have significant functional improvement after THA, objectively assessed by gait speed. Even if patients did not fully recover to the level of a healthy control person after THA, functional gain is comparable irrespective of BMI.