Biomechanical study of adjacent intervertebral motion after lumbar spinal fusion and flexible stabilization using polyethylene-terephthalate bands.

Thirty fresh-frozen calf cadaveric spinal specimens (L3-L6) were used to investigate the effect of flexible stabilization and fixation on the adjacent intervertebral motion segment. The intact spine that had not been subjected to injury was used for comparison as control. The destabilized spine was made up of specimens from which the bilateral facet joints and the supraspinous and interspinous ligaments were removed. The flexible stabilized spine was applied with pedicle screws and polyethylene-terephthalate bands, and the fixed spine was applied with pedicle screws and rods at the L4-L5 segment. The range of motion (ROM) was measured under flexion, extension, and bilateral bending moments, and the ROM ratio (ROM of each model versus ROM of the comparison model) was calculated at L3-L4, L4-L5, and L5-L6 segments. In the flexible stabilized spine, the restriction of motion was high under flexion and bilateral bending moments, and the mobility of the adjacent intervertebral motion segments approximated the normal lumbar vertebra. In the fixed spine, the ROM ratio increased at the cranial and caudal adjacent segments.