A non-invasive technique for assessing innominate bone motion

Objective. To determine the suitability of a magnetic tracking device to measure pelvic bone range of motion based on palpated and digitized pelvic landmarks. Design. A repeated measures study was conducted in two experiments to determine the reliability and validity of innominate bone range of motion measured with a magnetic tracking device in healthy subjects through passive hip abduction and external rotation. Background. Because of the anatomical position of the pelvic joints, kinematic analysis of joint motion is difficult. Accurate and precise measurements typically require highly invasive techniques involving implantation of titanium markers and exposing the subject to multiple radiographs. There is a need for a practical and accurate measurement method that will allow researchers and clinicians to accurately and reliably evaluate motion in the pelvis. Methods. Innominate bone angles were measured for two static hip postures from the 3D spatial coordinates of the pelvic landmarks. By palpating and subsequently digitizing pelvic landmarks using an electro-magnetic tracking device the 3D coordinates were obtained. Palpated results were validated using CT scans and a metallic bead attached to the palpated landmarks. Results. The mean range of innominate bone motion was between 3° and 4° (transverse plane) for each side with large variability across the subjects in the range of motion. Despite this variability, the measurements were found to be reliable and valid.