Engineering Center for Orthopedic Research Excellence (E-CORE), Departments of Bioengineering and Orthopaedic Surgery, University of Toledo, Toledo, Ohio, USA; Department of Orthopaedic Surgery, Nihon University Itabashi Hospital, Tokyo, Japan.
Engineering Center for Orthopedic Research Excellence (E-CORE), Departments of Bioengineering and Orthopaedic Surgery, University of Toledo, Toledo, Ohio, USA.
World Neurosurg. 2022 Nov;167:e962-e971. doi: 10.1016/j.wneu.2022.08.119. Epub 2022 Sep 5.
Sagittal balance is an important clinical parameter of the spine for its normal function. Maintenance of the sagittal balance is crucial in the clinical management of spinal problems.
Three different finite element models with spinal alignments based on Schwab's classification were developed: (1) Balanced/Normal model (sagittal vertical axis [SVA] = 0 mm, lumbar lordosis [LL] = 50°, thoracic kyphosis [TK] = 25°, pelvic incidence [PI] = 45°, pelvic tilt [PT] = 10°, sacral slope [SS] = 35°); (2) Balanced with compensatory mechanisms/Flatback model (SVA = 50 mm, LL = 20°, TK = 20°, PI = 45°, PT = 30°, SS = 15°); and (3) Imbalanced/Hyperkyphotic model (SVA = 150 mm, LL = -5°, TK = 25°, PI = 45°, PT = 40°, SS = 5°). All 3 models were subjected to the follower loads simulating bodyweight/muscular contractions along with the moments to simulate flexion, extension, lateral bending, and axial rotation. The maximum cortical vertebral stress, annular stress, and intradiscal pressure (IDP) were calculated and compared.
The results showed that the hyperkyphotic model had higher stresses in the vertebrae (25% higher), the annulus fibrosus (48% higher) and the IDP (8% higher) than the normal models in flexion. The segments near the thoracolumbar junction (T10-L1) showed the highest increase in the vertebral body stress, the annulus fibrosus stress, and the IDP.
This study showed that the imbalance in sagittal alignment might be responsible for disc degeneration and atraumatic vertebral fractures at the thoracolumbar regions, supporting clinical findings.
矢状平衡是脊柱正常功能的一个重要临床参数。维持矢状平衡对于脊柱问题的临床治疗至关重要。
根据 Schwab 分类，建立了三种具有不同脊柱排列的有限元模型：（1）平衡/正常模型（矢状垂直轴[SVA]=0mm，腰椎前凸[LL]=50°，胸椎后凸[TK]=25°，骨盆入射角[PI]=45°，骨盆倾斜角[PT]=10°，骶骨倾斜角[SS]=35°）；（2）平衡与代偿机制/平背模型（SVA=50mm，LL=20°，TK=20°，PI=45°，PT=30°，SS=15°）；（3）不平衡/过度后凸模型（SVA=150mm，LL=-5°，TK=25°，PI=45°，PT=40°，SS=5°）。所有 3 种模型均受到模拟体重/肌肉收缩的随动载荷以及模拟屈伸、侧屈和轴向旋转的力矩的作用。计算并比较了最大皮质骨椎体应力、环形应力和椎间盘内压（IDP）。
结果表明，在屈伸时，过度后凸模型的椎体（高 25%）、纤维环（高 48%）和 IDP（高 8%）的应力均高于正常模型。胸腰椎交界处（T10-L1）附近的节段，椎体骨应力、纤维环应力和 IDP 的增加最高。
本研究表明，矢状排列的不平衡可能是导致胸腰椎区域椎间盘退变和无创伤性椎体骨折的原因，支持临床发现。
