Lebl Darren R, Meyers Kathleen N, Altorfer Franziska C S, Jahandar Hamidreza, Pazionis Theresa J C, Nguyen Joseph, O'Leary Patrick F, Wright Timothy M
Department of Spine Surgery, Hospital for Special Surgery, New York, NY, USA
Department of Biomechanics, Hospital for Special Surgery, New York, NY, USA.
Int J Spine Surg. 2024 Jul 4;18(3):249-257. doi: 10.14444/8605.
Anterior cervical discectomy and fusion (ACDF) is known to elicit adverse biomechanical effects on immediately adjacent segments; however, its impact on the kinematics of the remaining nonadjacent cervical levels has not been understood. This study aimed to explore the biomechanical impact of ACDF on kinematics beyond the immediate fusion site. We hypothesized that compensatory motion following single-level ACDF is not predictably distributed to adjacent segments due to compensation from noncontiguous levels.
Six fresh-frozen cervical spines (C2-T1) underwent fluoroscopic screening and sagittal and coronal reformats from computed tomography scans and were utilized to grade segmental degeneration. Each specimen was tested to 30° of flexion and extension intact and following single-level ACDF at the C5-C6 level. The motions of each vertebral body were tracked using 3-dimensional (3D) motion capture into an inverse kinematics model, facilitating correlations between the 3D reconstruction from computed tomography images and the 3D motion capture data. This model was used to calculate each level's flexion/extension range of motion (ROM).
Single-level fusion at the C5-C6 level across all specimens resulted in a significant motion reduction of -6.8° ( = 0.002). No significant change in ROM occurred in the immediate adjacent segments C4-C5 ( = 0.07) or C6-C7 ( = 0.15). Hypermobility was observed in 2 specimens (33%) exclusively in adjacent segments. In contrast, the other 4 spines (66%) displayed hypermobility at noncontiguous segments. Hypermobility occurred in 42% (5/12) of the adjacent segments, 28% (5/18) of the noncontiguous segments, and 50% (3/6) of the cervicothoracic segments.
Single-level ACDF impacts ROM beyond adjacent segments, extending to noncontiguous levels. Compensatory motion, not limited to adjacent levels, may be influenced by degenerative changes in noncontiguous segments. Surprisingly, hypermobility may not occur in adjacent segments after ACDF.
Overall, the multifaceted biomechanical effects of ACDF underscore the need for a comprehensive understanding of cervical spine dynamics beyond immediate adjacency, and it needs to be taken into consideration when planning single-level ACDF.
已知颈椎前路椎间盘切除融合术（ACDF）会对紧邻节段产生不良生物力学影响；然而，其对其余非相邻颈椎节段运动学的影响尚不清楚。本研究旨在探讨ACDF对融合部位以外节段运动学的生物力学影响。我们假设，由于非连续节段的代偿作用，单节段ACDF后的代偿运动不会以可预测的方式分布到相邻节段。
对6个新鲜冷冻的颈椎（C2-T1）进行荧光透视筛查，并对计算机断层扫描进行矢状位和冠状位重建，用于对节段退变进行分级。每个标本在完整状态下以及在C5-C6节段进行单节段ACDF后，分别测试至30°的屈伸运动。使用三维（3D）运动捕捉将每个椎体的运动跟踪到逆运动学模型中，以促进计算机断层扫描图像的3D重建与3D运动捕捉数据之间的相关性。该模型用于计算每个节段的屈伸活动度（ROM）。
所有标本在C5-C6节段进行单节段融合后，运动显著减少了-6.8°（P = 0.002）。紧邻的C4-C5节段（P = 0.07）或C6-C7节段（P = 0.15）的ROM没有显著变化。在2个标本（33%）中，仅在相邻节段观察到活动过度。相比之下，其他4个脊柱（66%）在非连续节段表现出活动过度。活动过度发生在42%（5/12）的相邻节段、28%（5/18）的非连续节段和50%（3/6）的颈胸节段。
单节段ACDF会影响相邻节段以外的ROM，延伸至非连续节段。代偿运动不限于相邻节段，可能受非连续节段退变变化的影响。令人惊讶的是，ACDF后相邻节段可能不会出现活动过度。
总体而言，ACDF的多方面生物力学影响强调了全面了解颈椎动力学的必要性，而不仅仅是紧邻节段，在计划单节段ACDF时需要考虑这一点。
