Kinematics of the Human Pelvis Following Open Book Injury

Abstract

The objective of this study is to determine the three dimensional kinematics of the human pelvis including both sacroiliac joints following a simulated open book fracture induced on cadavers by applying anterior-posterior compressive loads to the pelvis. An electromagnetic digitizing and motion tracking system was utilized to measure the morphology of the pelvis and the relative movements of its bones during this simulated open book fracture. The screw displacement axis method was used to describe the relative motions between the sacrum and each hip bone. Morphologically, it was found that the articular surfaces forming the sacroiliac joints can be approximated with planar surfaces directed from proximal and lateral to distal and medial and from posteromedial to anterolateral. The kinematic data indicate that the motion of the hip bone with respect to the sacrum on the side of the sacroiliac joint (SIJ) opening is almost a pure rotation which translates clinically on the A-P x-rays as pure opening of the SIJ without vertical displacement. The average axis of rotation was found to be almost parallel to the SIJ planar articular surface.