EFFECTS OF METHOD OF INTERNAL-FIXATION OF SYMPHYSEAL DISRUPTIONS ON STABILITY OF THE PELVIC RING

This study tested different methods of internal fixation of a symphyse al 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 Lit two levels of the posterior sacr oiliac complex, was measured using high resolution displacement transd sucers. The fixations tested were (1) double plating (4.5 mm reconstru ction plates), (2) wire loops around two 6.5 mm, fully threaded cancel lous screws, and (3) an absorbable suture material (polydioxanone). Ea ch pelvis was first tested intact, recording displacements in response to a cyclic axial load up to a maximum of 500 N applied through the p roximal 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 fracture with lag scr ews and sequential fixation of the symphysis with each of the test met hods. The results from eight pelves revealed that internally fixed sym physeal motion was generally greater than intact, regardless of fixati on method. The superior symphysis was usually compressed while there w as distraction inferiorly. Wiring resulted in significantly less symph yseal motion than the other methods (P < 0.02), provided four loops we re used reducing the separation inferiorly. There was no significant d ifference in sacral fracture motion between the three methods. The res ults indicate that in osteoporotic bone, as used in this study, symphy seal wiring is best able to oppose the tensile loads in the inferior s ymphysis that are associated with bilateral stance loading. These biom echanical findings must be interpreted within the broader context of s urgical management of these complex injuries.