SHORT SEGMENT TRANSPEDICULAR COTREL-DUBOUSSET INSTRUMENTATION - A PORCINE CORPECTOMY MODEL

This study examines changes in stiffness in a three-level spinal const ruct utilizing transpedicular Cotrel-Dubousset instrumentation. In add ition, we evaluated the effect of adding offset laminar hooks at the s ame level as the superior transpedicular fixation. Porcine lumbar spin es(L-1 to L-5) were tested as (a)intact spine, (b) intact spine with i nstrumentation, and (c) instrumented spine after L-3 corpectomy. Instr umented constructs were tested with and without laminar hooks placed a t the level of superior transpedicular fixation. Constructs were teste d in modes of axial compression and torsion in a MTS materials testing machine. The fully instrumented intact spines demonstrated a 28.0% st iffness increase.over the intact spines in torsion (p < 0.005) and a 2 3.1% increase in the mode of axial compression (p < 0.0002). There was no statistically significant difference in axial or torsional stiffne ss in the instrumented intact spine constructs when hooks were added. In the corpectomy model, addition of the laminar hooks increased stiff ness in axial compression an average of 26.9% (p < 0.002) and in torsi on an average of 28.1% (p < 0.0005). This increase in stiffness may ai d in preventing the postoperative progression of kyphosis noted in stu dies utilizing similar constructs in clinical application for the trea tment of lumbar burst fractures.