STABILITY OF OPEN-BOOK PELVIC FRACTURES USING A NEW BIOMECHANICAL MODEL OF SINGLE-LIMB STANCE

Objective: A new biomechanical model of single-limb stance was develop ed to test the stability of intact, injured, and internally fixed pelv es. Design: Single-limb stance was simulated by applying muscle forces and body mass loading to cadaver pelves. We created a rotationally un stable ''open-book'' pelvic injury in nine embalmed pelves by dividing the ligaments of the pubic symphysis, pelvic floor, and anterior and interosseus sacroiliac joint. All pelves were devoid of gross structur al abnormalities. Intervention: Two methods of internal fixation of th e pubis symphysis were compared: (a) a curved six-hole 3.5-millimeter reconstruction plate across the superior pubic symphysis, and (b) the same six-hole 3.5-millimeter reconstruction plate plus a perpendicular ly oriented four-hole 3.5-millimeter reconstruction plate placed acros s the anterior symphysis. Main Outcome Measurements: We measured verti cal shear displacement at the pubic symphysis and horizontal displacem ent at the anterior sacroiliac joint. The results for the injured and fixed specimens were compared with each other and with the results for the intact specimens. Results: The injured unfixed specimens showed m arked instability that was prevented by both methods of fixation of th e pubic symphysis. No significant differences could be demonstrated be tween single and double plating of the disrupted pubic symphysis when using this single-limb stance model. Conclusion: This model of single- limb stance suggests that a single symphyseal plate across the pubic s ymphysis can stabilize the open-book injury under short-term quasi-sta tic loads.