Biomechanical study of the influence of different degrees of pubic symphysis diastasis on stress distribution of the posterior pelvic ring

Objective To evaluate the effect of different degrees of pubic symphysis diastasis on the stress distribution of posterior pelvic ring. Methods Eight embalmed pelvis and articulated proximal 1/3 of the femurs were harvested for this study. The samples were positioned as both legs standing straight and loaded to 600 N on the on the CSS-44020 biomechanical machine. The strain gages were adhered to 38 sites distributed symmetrically on the two sides of sacroiliac joint, anterior sacrum and posterior ilium. The strain gages were connected to WS3811 digital strainometer to record strain changes of the intact pelvic ring and at 1,2, 2.5 cm of pubic symphysis diastasis. Results Elastic changes occurred in the cortical bone of the pelvis under 600 N load. The symmetrical sites had similar strain changes without significant difference in the intact pelvic ring and at 1,2, 2.5 cm of pubic symphysis diastasis ( P ＞0.05 ). The sites with more strain changes were distributed on the iliofemoral arch in the intact pelvis.The strain changes were increased significantly frona the posterolateral sites to the iliofemoral arch. But the strain changes on the iliofemoral arch were decreased significantly during pubic symphysis diastasis.Conclusion The conduction of vertical load runs along the sacrofemoral arch in the intact pelvic ring and redistributes posterolaterally during pubic symphysis diastasis. Key words: Pubic symphysis diastasis;  Biomechanics;  Strain