Computer aided design and evaluation of new anatomic fixation system on entire pelvic model

Abstract

This paper presented a special computer aided procedure to design a new sacroliliac anatomic bar-plate internal fixation system, and evaluated its biomechanical properties on an accurate patient-specific finite element model of entire pelvis, compared with two conventional internal fixation methods. Based on virtual anatomical measure of 30 digital pelvic models reconstructed from CT, an anatomic plate was designed according to the complicated structure of the outer table of the posterior ilium, and was integrated into the complete fixation system. Then, an ad hoc semi-automatic mesh generator was employed to construct a patient-specific finite element model of whole pelvis, including elaborate sacroiliac joints, important pelvic ligaments, and interpubic disc, as well as position-dependent cortical thickness and trabecular bone elastic modulus. Following, one side of sacroiliac joint related ligaments were deleted to simulate a complete unilateral sacroiliac joint disruption. Then the new anatomic fixation system was integrated to fix the fracture, and two comparing models including iliosacral screw fixation and front reconstruction plate fixation were also generated. Finally, all models were simulated under same loading conditions. The results demonstrated that the mechanical stability of the new anatomic fixation system was superior, with obviously improved stress distribution and little displacement, which implied an effective internal fixation method for potential clinical application.