Effect of limited range of motion of the hip joint and leg-length discrepancy on gait trajectory: an experiment to reproduce the asymmetric gait that occurs in patients with osteoarthritis of the hip joint

Purpose: Although some symptoms that often occur with hip joint osteoarthritis (OA) may be involved in the appearance of gait disturbance, the main cause has not been identified. We hypothesised that the abnormalities in gait trajectory of patients with hip joint OA are mainly caused by limited range of motion of the hip joint or the presence of leg-length discrepancy, or both. To investigate this hypothesis, we examined whether the abnormal gait trajectory in patients with hip joint OA can be reproduced in healthy individuals by asking them to wear a hip orthosis and shoe orthotic (insole). Methods: We recruited 2 groups of participants: patients with hip joint OA (OA group, 38 patients) and healthy individuals who imitated patients with OA of the hip joint by wearing a hip orthosis or shoe orthotic (10-mm or 20-mm insole) or both (simulated OA group, 6 individuals). For gait analysis, we used a portable, wearable gait analyser with inertial sensors to evaluate 3-dimensional (3D) changes in gait trajectory. Results: In the OA group, the patterns of gait trajectories that were drawn on the 3 planes (coronal, sagittal, and horizontal planes) could be roughly divided into 3 types. The gait trajectories that were drawn when wearing a hip orthosis in the simulated OA group were very similar to 1 of the 3 patterns of gait trajectory that occurs in the OA group. Conclusions: We were able to reproduce the abnormal gait trajectory that is observed in ⅓ of patients with hip OA in healthy individuals, so we propose that an extreme reduction in hip joint ROM is 1 of the causes of abnormal gait pattern in patients with OA of the hip joint. A difference in leg length of 20 mm alone has little effect on gait trajectory.