Inter-joint coordination of kinematics and kinetics before and after total hip arthroplasty compared to asymptomatic subjects.
While differences in joint kinematics and kinetics between control subjects and patients before and after total hip arthroplasty (THA) has often been studied, inter-joint coordination has not been fully characterized. We hypothesized that in patients undergoing THA, inter-joint coordination (i) is different from control subjects before surgery, (ii) changes from pre-operative to post-operative, and (iii) remains different from control subjects after surgery. Seventy-eight subjects underwent gait analysis before and ∼1 year after primary unilateral THA. 109 control subjects were age, sex, and BMI matched to the THA group. We selected a representative trial at each subjects' self-selected walking speed from a motion analysis data repository. To assess kinematic coordination, we constructed sagittal plane hip-knee angle cyclograms, and calculated total, stance, and swing phase plot area (deg2). To assess kinetic coordination, we calculated the support moment (MS, %wt ∗ ht), the time-integral of support moment (MS impulse, %wt ∗ ht ∗ t), and the relative contribution of each joint to MS impulse (%Hip, %Knee, %Ankle). We used t-tests to compare groups. Total and swing-phase cyclogram area was smaller preoperatively, but improved to control values after THA. Swing-phase area was smaller than control values after THA. MS impulse was larger in THA subjects than controls both before and after surgery. While, the relative contribution of the hip to MS impulse was not different from control values, the contributions of the knee and ankle were smaller. Inter-joint coordination, as measured by hip-knee angle cyclograms and MS impulse, may be used to distinguish differences in gait mechanics between osteoarthritis and THA. Future work focusing on coordination among joints may be needed to fully restore gait function.