Internal fixation of bilateral sacroiliac dislocation with transiliac locked plate: a biomechanical study on pelvic models

The purpose of this study was to analyze and compare the mechanical characteristics of a new iliosacral fixation technique (bilateral S1 pedicle fixation through a transiliac locked plate) for bilateral sacroiliac dislocations with other previously described methods. Bilateral sacroiliac dislocations were created in 21 pelvic models and divided into three different fixation method groups. Group 1 was fixed using posterior tension band plating with a 3.5 mm locked plate combined with fixed-angle locked 3.5 mm screw fixation of bilateral S1 vertebra pedicles through suitable holes of the plate. Group 2 underwent posterior tension band plating with a 3.5 mm locked plate combined with bilateral spongious iliosacral screw fixation and Group 3 bilateral iliosacral spongious screw fixation alone. The ultimate load to failure and load for 10 mm of displacement for all three groups were compared. The average loads to failure for Groups 1, 2 and 3 were 1775, 2084 and 2230 N, respectively, and average loads for 10 mm of displacement were 1033, 1884 and 2013 N, respectively. Group 2 and 3 had the strongest fixation constructs although there was no statistically significant difference between these two groups (p=0.452). Group 2 and 3 were superior to Group 1 in terms of loads for 10 mm of displacement. There was no significant difference between Group 2 and 3 in this regard (p=0.397). Iliosacral screws are superior to bilateral S1 pedicle fixation through posterior tension band plating. However, the combination of tension band plating with iliosacral screw fixation does not improve the stability of the posterior pelvic ring.