Effect of cam-type femoroacetabular impingement on hip joint kinematics

Cam-type femoroacetabular impingement is a painful disorder common in young adults, caused by decreased concavity of the femoral head-neck. It is associated with hip osteoarthritis, though the exact mechanism of joint damage is not fully understood. Gait analysis has shown that cam deformities cause changes to coupled motions in vivo, though it is unclear whether these changes are compensatory or due to direct bony contact. The objective of this study was to determine how cam deformities and surgical resection affect patterns of hip rotation, translation of the center of rotation, and force required to flex and abduct the hip. We assessed the relationship between deformity and coupled motions, translations of center of femoral rotation, and force required to create active unconstrained flexion and abduction ex vivo. Three deformities were simulated on each of six hemi-pelvis/proximal femur specimens. Four muscles were simulated by cables drawn from the distal tendon to the location of proximal attachment. Motion was created by actively shortening one of these cables while statically loading the others. Markers on the femur and pelvis were tracked, allowing for calculation of joint rotations and translations. A load cell on the active cable allowed for measurement of the applied force. We found that deformity resulted in increased external rotation, adduction and translation during flexion and increased internal rotation, extension and decreased translation during abduction. We also found that when a more severe deformity was present, more force was required to create both flexion and abduction to the same angle. Further, we found that resection resulted in increased internal rotation and translation during flexion and decreased internal rotation during abduction. Less force was required to create flexion and abduction following resection. Changes to motion patterns occur as a result of changed contact loads between the femoral head and acetabulum, resulting in loading of regions of articular cartilage which may not be optimized for these loads and may, therefore, begin a degenerative cascade leading to osteoarthritis. As coupled motions were observed within ranges of flexion and abduction required for daily living, it is recommended that resection be performed in an attempt to slow the progression of osteoarthritis by limiting contact between the femoral head-neck and acetabulum.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat