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 ( = .03) and posterior motion in the sagittal plane ( < .01) but not composite motion ( = .37). Motion in the axial plane was in an inferior direction ( = .08). Cam morphology significantly changed rotation in the sagittal plane ( < .01) but not in the coronal ( = .63) or axial plane ( = .18). Composite motion was related to the amount of torque applied to the hip ( < .01). The amount of torque applied to the hip was related to rotation in the coronal plane ( < .01), axial plane ( < .01), and sagittal plane ( < .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.