In-vitro validation of a non-invasive dual fluoroscopic imaging technique for measurement of the hip kinematics.

Measurement of accurate in vivo hip joint kinematics in 6-DOF is difficult. Few studies have reported non-invasive measurements of the hip kinematics. The objective of this study was to validate a non-invasive dual fluoroscopic imaging system (DFIS) for measurement of hip kinematics. Bi-lateral hip joints of a cadaveric pelvic specimen were CT scanned to create bone models of the femur and pelvis, and subsequently tested in static and dynamic conditions inside the DFIS. The poses of the hip in space were then determined by matching the bone models with the fluoroscopic images. The pose data was compared to those obtained using a radio-stereometric analysis to determine the accuracy of the DFIS. The accuracy ± precision for measuring the hip kinematics were less than 0.93 ± 1.13 mm for translations and 0.59 ± 0.82° for rotations in all conditions. The repeatability of the DFIS technique was less than ± 0.77 mm and ± 0.64° in position and orientation for measuring hip kinematics in both static and dynamic positions. This technique could thus be a promising tool for determining 6-DOF poses of the hip during functional activities, which may help to understand biomechanical factors in hip pathologic conditions such as osteoarthritis and femoroacetabular impingement before and after surgical treatment.