Effect of spinous process excision on adjacent segment motion: A biomechanical study

Abstract

Adjacent Segment Disease (ASD) is associated with poor surgical outcomes and early revision surgery after spinal fusion. The relative contributions of rigid instrumentation and destabilization due to laminectomy as independent factors of ASD are unclear; clinical studies often include patients that have undergone both. The objective of this study is to compare the biomechanical effect of laminectomy versus posterior instrumentation on adjacent segment motion (ASM). Five fresh-frozen porcine lumbar spines were mounted on an Instron loading machine and cyclically flexed. Each specimen underwent a phase with instrumentation spanning the operative level followed by a phase without instrumentation, but with a modified laminectomy (spinous process excision without violation of the facet joints). In both phases, ASM was measured during application of a flexion moment. The study revealed that ASM after laminectomy was significantly higher than after inter-segmental instrumentation (3.64mm vs. 1.76mm more than control; p=0.04), and significantly higher than control (p=0.04). Although ASM after inter-segmental instrumentation was greater than controls, it was not significant (p=0.07). Modified laminectomy in this porcine model causes a significant increase in motion at the adjacent lumbar segment compared with both rigid instrumentation alone and controls. This emphasizes the role of the posterior spinal elements in lumbar stability and implicates laminectomy as a greater risk for causing ASM than fusion. © 2009 Springer Berlin Heidelberg.