Park Dong-Hyuk, Ramakrishnan Prem, Cho Tai-Hyoung, Lorenz Eric, Eck Jason C, Humphreys S Craig, Lim Tae-Hong
Department of Neurosurgery, Korea University Hospital, Seoul, Korea.
J Neurosurg Spine. 2007 Sep;7(3):336-40. doi: 10.3171/SPI-07/09/336.
Symptomatic multisegment disease is most common at the C5-6 and C6-7 levels, and two-level anterior cervical discectomy and fusion (ACDF) is performed most often at these levels. Therefore, it may be clinically important to know whether a C5-7 fusion affects the superior C4-5 segment. A biomechanical study was carried out using cadaveric cervical spine specimens to determine the effect of lower two-level anterior cervical fusion on intradiscal pressure and segmental motion at the superior adjacent vertebral level.
Five cadaveric cervical spine specimens were used in this study. The specimens were stabilized at T-1 and loaded at C-3 to 15 degrees flexion, 10 degrees extension, and 10 degrees lateral bending before and after simulated two-level ACDF with plate placement at C5-7. Intradiscal pressure was recorded at the C4-5 level, and segmental motion was recorded from C-4 through C-7. Differences in mean intradiscal pressures were calculated and analyzed using a paired Student t-test. When the maximum calibrated intradiscal pressures were exceeded ("overshot") during measurements, data from the specimens involved were analyzed using the motion data with a Student t-test. Values for pressure and motion obtained before and after simulated ACDF were compared.
During flexion, the mean intradiscal pressure changes (+/- standard deviations) in the pre- and post-ACDF measurements were 1275 (+/- 225) mm Hg and 2475 (+/- 75) mm Hg, respectively (p < 0.05). When the results of pre-ACDF testing were compared with post-ACDF results, no significant difference was found in the mean changes in the intradiscal pressure during extension and lateral bending. The maximum calibrated intradiscal pressures were exceeded during the post-ACDF testing in four specimens in extension, three in flexion, and two in lateral bending. Comparison of pre- and post-ACDF data for all five specimens revealed significant differences in motion and intradiscal pressure (p < 0.05) during flexion, significant differences in motion (p < 0.05) but not in intradiscal pressure during extension, and significant differences in intradiscal pressure changes (p < 0.05) but not in motion during lateral bending.
Simulated C5-7 ACDF caused a significant increase in intradiscal pressure and segmental motion in the superior adjacent C4-5 level during physiological motion. The increased pressure and hypermobility might accelerate normal degenerative changes in the vertebral levels adjacent to the anterior cervical fusion.
有症状的多节段疾病最常见于C5 - 6和C6 - 7节段，两级颈椎前路椎间盘切除融合术（ACDF）最常在此节段进行。因此，了解C5 - 7融合是否会影响上方的C4 - 5节段可能具有临床重要性。本研究使用尸体颈椎标本进行生物力学研究，以确定下两级颈椎前路融合对相邻上位椎体节段椎间盘内压力和节段运动的影响。
本研究使用了5个尸体颈椎标本。在T - 1处固定标本，并在C5 - 7节段模拟两级ACDF并放置钢板前后，在C - 3处加载，使其进行15度前屈、10度后伸和10度侧弯运动。记录C4 - 5节段的椎间盘内压力，并记录C - 4至C - 7节段的节段运动。使用配对学生t检验计算并分析平均椎间盘内压力的差异。当测量过程中超过最大校准椎间盘内压力（“超限”）时，对涉及的标本数据使用运动数据并通过学生t检验进行分析。比较模拟ACDF前后获得的压力和运动值。
在前屈过程中，ACDF术前和术后测量的平均椎间盘内压力变化（±标准差）分别为1275（±225）mmHg和2475（±75）mmHg（p < 0.05）。将ACDF术前测试结果与术后结果进行比较时，后伸和侧弯过程中椎间盘内压力的平均变化未发现显著差异。在ACDF术后测试中，后伸时有4个标本、前屈时有3个标本、侧弯时有2个标本超过了最大校准椎间盘内压力。对所有5个标本的ACDF术前和术后数据进行比较发现，前屈过程中运动和椎间盘内压力存在显著差异（p < 0.05），后伸过程中运动存在显著差异（p < 0.05）但椎间盘内压力无显著差异，侧弯过程中椎间盘内压力变化存在显著差异（p < 0.05）但运动无显著差异。
模拟C5 - 7 ACDF在生理运动过程中导致相邻上位C4 - 5节段的椎间盘内压力和节段运动显著增加。压力增加和活动过度可能会加速颈椎前路融合相邻椎体节段的正常退变。
