BIOMECHANICAL SIMULATION OF THE ANTEROPOSTERIOR COMPRESSION INJURY OFTHE PELVIS - AN UNDERSTANDING OF INSTABILITY AND FIXATION

Seven fresh cadaveric pelvic specimens were biomechanically analyzed. Testing was first performed on intact pelves and then after progressiv e disruption of the (1) symphysis pubis, (2) unilateral anterior and i nterosseous sacroiliac ligaments and capsule, (3) ipsilateral sacrospi nous and sacrotuberous ligaments; and fixation with a 4.5-mm narrow dy namic compression plate at the symphysis pubis, or a 4.5-mm narrow dyn amic compression plate at the anterior sacroiliac joint with and witho ut the symphysis pubis plate, or a 7.0-mm sacroiliac lag screw anchore d into the S1 vertebral body with and without the symphysis pubis plat e. Symphyseal gapping occurred after isolated symphysis pubis disrupti on. With additional disruption of the unilateral sacroiliac joint liga ments, symphysis pubis displacement was unaffected; however, the injur ed sacroiliac joint gap displacement, and sacroiliac joint flexion ang ulation on both intact and injured sides increased as compared to the specimen in the intact state. Further disruption of the ipsilateral sa crotuberous and sacrospinous ligament complex produced little addition al motion at either symphysis pubis or sacroiliac joints. Plate fixati on of the symphysis pubis alone reduced symphysis pubis motion, but no t sacroiliac motion. Use of sacroiliac fixation alone without a symphy sis pubis plate did not affect symphysis pubis motion. The symphysis p ubis plate is the key to stabilizing symphysis pubis motion, and simil arly, sacroiliac joint fixation is required to control sacroiliac join t motion. Both single iliosacral screws and plates produced equivalent decreases in sacroiliac joint motion.