The relationship of coronal trunk motion on the hip abductor moment impulse in pre-operative hip pathology patients during walking

Background: Compensatory mechanisms for hip pain, pathology, and weakness include excessive trunk lean towards the stance limb, counteracting pelvic drop to maintain stability during single leg stance. Trunk lean shifts the center of mass towards the hip joint center to decrease the moment arm and reduce hip abductor demand. The purpose of this study was to evaluate whether adolescent patients with symptomatic hip pain demonstrate excessive trunk lean and the effect on the hip abductor moment impulse. Methods: Self-selected speed walking data collected through an approved study were reviewed on pre-operative patients clinically diagnosed with a hip deformity. Instrumented motion analysis was performed to analyze trunk kinematics and the hip abductor moment impulse. Findings: There was a weak, but significant correlation between hip abductor moment impulse and trunk lean. Patients diagnosed with Acetabular Dysplasia demonstrated an increased trunk lean and a decreased hip abductor moment impulse (r = − 0.311, p = 0.001). Of those who presented with excessive trunk lean, 62% of these patients had a normal hip abductor moment impulse. There was no correlation between hip abductor moment impulse and hip abductor strength. Interpretation: Excessive trunk lean was not seen uniformly across adolescent patients with symptomatic hip deformities, despite pain being reported in 80% of patients. Furthermore, a majority of those that presented with excessive trunk lean did not present with a reduced moment, suggesting that although the amount of lean was greater than normal, it was not enough to significantly reduce the demand on the hip musculature.