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2018 Abstracts

Kinematics of Hip Joints with Cam Femoroacetabular Impingement

Joseph Hartle, University of Utah

Femoroacetabular impingement (FAI) is one of the most prevalent causes of osteoarthritis of the hip. Cam FAI is an orthopaedic pathology characterized by abnormal bony growth on the femoral head-neck junction. Cam FAI is thought to limit range of motion, which may result in chondral lesions and extensive labral tears. The purpose of this project was to quantify the variance in kinematics and the location of the hip joint center (HJC) between hip joints with cam FAI and asymptomatic controls using dual fluoroscopy (DF). For this DF study, 6 cam FAI patients and 11 control subjects were recruited. For each subject, hip joint kinematics were determined using DF. First, computed tomographic (CT) images were obtained for each subject. The images were segmented to delineate the bony surfaces and converted to 3D digitally reconstructed radiographs (DRRs). For the capture of bone movement, subjects performed activities in the combined field of view of two fluoroscopes, which collect x-ray video data. Specifically for identification of the HJC, subjects performed the StarArc pattern with their leg. This activity provided a large range of motion that allowed accurate determination of hip joint kinematics and the HJC location. After data capture, the DRR was matched to the DF data during the markerless tracking process. The data was processed in Matlab to provide visualization of the kinematics using subject-specific bone reconstructions in Postview. Abnormal, aspherical morphology of the femoral head in patients with cam FAI may cause the femoral head to translate more within the joint while also limiting the range of movement. Therefore, patients with cam FAI are expected to display a greater degree of translational motion of the HJC and a lower degree of rotational motion than control subjects. DF techniques provide arthrokinematics of the hip, which is how the joint moves in vivo relative to subject-specific bone anatomy. Using this data as a gold standard, errors in the calculation of the hip joint center using standard motion capture techniques can be measured. This method can be applied to help us better understand the kinematics of cam FAI and how the asphericity of the femoral head can cause pain and cartilage erosion which is associated with osteoarthritis.