BIOMECHANICS OF IN-SITU ROD CONTOURING OF SHORT-SEGMENT PEDICLE SCREWINSTRUMENTATION IN THE THORACOLUMBAR SPINE

In situ rod contouring is proposed as a means of three-dimensionally c ontrolling the three columns of the spine. Our goal was to determine t he biomechanical effectiveness of the technique for both clinical appl ication and future research. Six cadaver specimens were tested with pe dicle screw instrumentation from T12. to L2 in an L1 corpectomy model with all longitudinal ligaments retained across the defect. Contouring moment, anterior longitudinal ligament (ALL) forces, and distraction and lordosis across L1 were monitored, Rods were contoured to 26 degre es, and axial distraction averaged 6.9 mm. Bone/screw-interface Failur e began during contouring in every case <10 degrees with no resulting increase in lordosis across L1. High tensile forces generated in the A LL resisted the moment applied by the rod benders and instead caused f ailure of the weaker bone/screw interface.