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

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 ( 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.