Abstract: Objective To compare the stress distribution of posterior pelvic ring fixed with minimally invasive adjustable plate(MIAP)combined with one iliosacral(IS)screw and two IS screws.Methods Five embalmed specimens of adult pelvis were used.The soft tissue was removed from the specimens,and the spines from the fourth lumbar vertebra to the proximal one-third of both femurs were retained.The pubic symphysis,bilateral sacroiliac joints and ligments, bilateral hip joints,bilateral sacrotuberous ligaments and sacrospinous ligaments were intact.The strain gages were adhered to 32 sites distributed symmetrically.The specimens were placed in the biomecanical machine at a standing neutral posture.Vertical load up to 520 N was applied and the strain value of intact pelvic ring was recorded.The Tile C pelvic fractures were made.The symphysis pubis was fixed with plate,and the fracture of posterior pelvic ring was fixed with two kinds of internal fixators.The strain changes were recorded respectively.Results The symmetrical sites of the intact pelvic ring had similar strain changes(P >0.05).And the strain concentration sites ran along the sacrofemoral arch.Compared with the strain value of the intact pelvis,the strain changes of these sites(except site 5,6,10,11)in the pelvic fractures fixed with two kinds of internal fixation were not statistically significant(P > 0.05).Each strain value in the posterior pelvic ring fixed with MIAP combined with one IS screw was close to that in intact pelvis under 500 N vertical load.Conclusion In the intact pelvic ring,the conduction of vertical load runs along the sacrofemoral arch.The posterior pelvic ring fixed with MIAP combined with one IS screw can achieve better restoration of mechanical conduction than that fixed with two IS screws.

Key words: fracure fixation, biomechaincs, plevis