A pre-operative approach of range of motion simulation and verification for femoroacetabular impingement.

BACKGROUND Femoroacetabular impingement (FAI) is increasingly recognized as a potential cause of hip osteoarthritis. A system capable of pre-operatively simulating hip range of motion (ROM) by given surface models from either healthy or FAI diseased bone is desirable. METHODS An impingement detection system using bounding sphere hierarchies was first developed. Both precision and accuracy of the impingement detection system were verified by a custom-designed phantom to imitate ball-and-socket hip movement. The impingement detection system was then implemented into the hip ROM simulation system to simulate the ROM of (1) healthy pelvis and femur, and (2) healthy pelvis and pathologic femur. The ROM simulation system was also verified by manipulating sawbones under the navigation of an optical tracking system. RESULTS The impingement detection system achieved a distance error of 0.53 ± 0.06 mm and an angular error of 0.28 ± 0.03°. The impingement detection accuracies were 100%, 100%, and 96% in three different phantom orientations, respectively. The mean errors between simulated and verified ROM were 0.10 ± 1.39° for the 'healthy pelvis and femur' group, and - 2.38 ± 3.49° for the 'healthy pelvis and pathologic femur' group. CONCLUSION The present study demonstrates a pre-operative approach to virtually simulate and predict the functional hip ROM based on the given bone models. The impingement detection and ROM simulation systems developed may also be used for other orthopedic applications.