Total knee arthroplasty alters trunk alignment and reduces lumbar erector spinae activity during gait.

BACKGROUND

Patients with knee osteoarthritis often walk with increased forward trunk posture. Although trunk posture may change after total knee arthroplasty, changes in trunk and pelvic alignment and erector spinae activity during gait after total knee arthroplasty, and their associations with knee biomechanics, remain unclear. This study investigated changes in trunk and pelvic alignment and erector spinae activity during gait before and after total knee arthroplasty and examined their associations with knee joint biomechanics.

METHODS

Twenty-four patients who underwent primary total knee arthroplasty were evaluated preoperatively and 1 year postoperatively. Three-dimensional motion capture, force plates, and surface electromyography were used to quantify the dynamic sagittal vertical axis (C7-S1 anteroposterior distance), trunk inclination, pelvic tilt, knee kinematics, peak external knee flexion moment (normalized to body mass), and erector spinae activity (% maximum voluntary contraction).

FINDINGS: After total knee arthroplasty, the mean dynamic sagittal vertical axis and forward trunk inclination during gait decreased (p < 0.01), whereas the mean anterior pelvic tilt increased (p < 0.01). Moreover, erector spinae % maximum voluntary contraction decreased (p < 0.01), and peak external knee flexion moment increased (p = 0.03). Changes in the dynamic sagittal vertical axis were negatively correlated with changes in the peak external knee flexion moment (r = -0.49, p = 0.02).

INTERPRETATION: After total knee arthroplasty, dynamic sagittal vertical axis, trunk inclination, and erector spinae activity decreased during gait. Postoperative changes in trunk posture during gait were associated with knee joint kinetics but not with sagittal plane knee extension kinematics.