Kinematics of the whole lumbar spine. Effect of discectomy.

The biomechanical effects of discectomy on the motion behavior of whole lumbar spine are investigated using a Selspot II system. Fresh human ligamentous specimens were potted at the sacrum and clinically relevant loads (flexion/extension, right/left lateral bending, and right/left axial torsion moments) applied through a loading frame attached rigidly to the topmost vertebra of the specimen. The resulting three-dimensional motions of each vertebra for the intact specimen were recorded. The specimen was injured sequentially on the right side of the L4-5 level: partial laminectomy, partial facetectomy, subtotal discectomy, and total discectomy. The motion behavior of the specimen after each injury was recorded. The results of the injured tests were normalized with respect to the corresponding intact results. The normalized data for eight specimens were pooled for statistical analysis. Subtotal discectomy induced significantly less motion at the injury site than total discectomy, in all loading modes. At L3-4, the motion segment above the injury level, anteroposterior translation in flexion and lateral translation in left lateral bending show significant increases irrespective of the amount of nucleus excised. The clinical relevance of these findings are discussed.