Simulated Cam Morphology of the Hip Changes Sacroiliac Motion During Hip Motion and Loading in a Cadaveric Model

Abstract

Purpose: To determine the relationship between cam morphology of the hip and ipsilateral sacroiliac motion compared to the native hip in a cadaveric model. Methods: A simulated cam state was created using a 3-dimensional printed cam secured to the head-neck junction of 5 cadaveric hips. Hips were studied using a computed tomography–based optic metrology system and a 6 degree-of-freedom robot to exert an internal rotation torque at 3 different torque levels (6 N-m, 12 N-m, 18 N-m). Outcomes included translational and rotational movement about 3 axes and composite (total) translational motion at the ipsilateral sacroiliac (SI) joint. Statistical analysis included a linear mixed model regression with repeated measures. Results: The presence of a simulated cam was associated with medial motion in the coronal plane (P = .03) and posterior motion in the sagittal plane (P < .01) but not composite motion (P = .37). Motion in the axial plane was in an inferior direction (P = .08). Cam morphology significantly changed rotation in the sagittal plane (P < .01) but not in the coronal (P = .63) or axial plane (P = .18). Composite motion was related to the amount of torque applied to the hip (P < .01). The amount of torque applied to the hip was related to rotation in the coronal plane (P < .01), axial plane (P < .01), and sagittal plane (P < .01) with increased effects as torque increased. Torque was not associated with translation movement in any of the anatomic planes. Conclusions: The presence of simulated cam morphology is associated with motion in a more medial, inferior, and posterior direction at the ipsilateral SI joint relative to a native state. Increasing torque affects the magnitude of translation, but not its direction, which in this study is primarily influenced by cam morphology. Clinical Relevance: This biomechanical connection between cam-type femoroacetabular impingement syndrome and the ipsilateral SI joint provides insight into SI joint dysfunction in patients with femoroacetabular impingement syndrome.