Effects of method of internal fixation of symphyseal disruptions on stability of the pelvic ring

Abstract

This study tested different methods of internal fixation of a symphyseal disruption, in comparison with the mechanics of the intact pelvis. Unembalmed cadaveric pelves were tested in simulated bilateral stance in a servohydraulic materials-testing machine. Motion of the superior and inferior pubic symphysis, and at two lefels of the posterior sacroiliac complex, was measured using high resolution displacement transdsucers. The fixations tested were (1) double plating (4.5 mm reconstruction plates), (2) wire loops around two 6.5 mm, fully threaded cancellous screws, and (3) an absorbable suture material (polydioxanone). Each pelvis was first tested intact, recording displacements in response to a cyclic axial load up to a maximum of 500 N applied through the proximal sacrum. The pubic symphysis was then sectioned and the sacrum fractured to produce an unstable pelvis (Tile C-type). Recordings were then repeated, following fixation of the sacral fructure with lag screws and sequential fixation of the symphysis with each of the test methods. The results from eight pelves revealed that internally fixed symphyseal motion was generally greater than intact, regardless of fixation method. The superior symphysis was usually compressed, while there was distraction inferiorly. Wiring resulted in significantly less symphyseal motion than the other methods ( P<0.02), provided four loops were used, reducing the separation inferiorly. There was no significant difference in sacral fracture motion between the three methods. The results indicate that in osteoporotic bone, as used in this study, symphyseal wiring is best able to oppose the tensile loads in the inferior symphysis that are associated with bilateral stance loading. These biomechanical findings must be interpreted within the broader context of surgical management of these complex injuries.