• Raj D Rao, Mei Wang, Linda M McGrady, Thomas J Perlewitz, and Kenny S David.
• Department of Orthopaedic Surgery, Medical College of Wisconsin, Milwaukee, WI 53226, USA. rrao@mcw.edu
• Spine. 2005 Dec 15; 30 (24): 2788-92; discussion 2793.

Study DesignIn a human cadaveric model, the effects of plate supplementation on the mechanical behaviors of adjacent segments were investigated.ObjectivesThe objective was to determine the effects of anterior cervical fusion and plating on the adjacent segments.Summary Of Background DataIncreases in intradiscal pressure and intervertebral motion at adjacent segments have been reported in the lumbar spine following an instrumented fusion. It is unclear if the same phenomenon presents in the cervical spine.MethodsSeven human cadaveric cervical spines (C2-T1) were used, and fusion of the C5-C6 segment was chosen for the purpose of this study. Two miniature pressure transducers were implanted within each adjacent disc. Flexion, extension, lateral bending, and torsion loads up to 2.5 Nm were applied to the intact spine, and following each of the two procedures, anterior discectomy and grafted fusion, and anterior plating of the C5-C6 motion segment.ResultsAt the surgical level, a significant increase in segmental stiffness was observed after plating in all directions. Following the grafted fusion, there were no statistically significant changes at the superior adjacent segment, and there was a 13.7% increase in axial rotation in the inferior adjacent segment. Once anterior plating was applied, slight increase (<12%) over the intact spines was noted in lateral bending in both adjacent segments. However, there was no significant difference between the grafted fusion and anterior plated fusion at either adjacent segment. At both adjacent disc levels, the differences in intradiscal pressures between grafted fusion and plated fusion were less than 30% in all directions, and none of these differences was statistically significant.ConclusionsIntradiscal pressures and intervertebral motion at the adjacent levels are not significantly affected by the instrumented anterior fusion. The clinically observed degenerative change at adjacent segments in the cervical spine is more likely to be attributed to natural progression of the spondylotic process as opposed to biomechanical effect of the instrumentation or fusion.

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