• Koji Matsumoto, Anoli Shah, Amey Kelkar, Muzammil Mumtaz, Yogesh Kumaran, and Vijay K Goel.
• 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.
• World Neurosurg. 2022 Nov 1; 167: e962e971e962-e971.

BackgroundSagittal 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.MethodsThree 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.ResultsThe 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.ConclusionsThis 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.Copyright © 2022 Elsevier Inc. All rights reserved.

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