Biomechanical rational for development of cervical kyphosis deformity: a finite element analysis

Alterations in cervical curvature can redistribute stress and strain among intervertebral discs (IVDs), facet joints, and neck muscles, potentially initiating degenerative changes that contribute to the development of cervical kyphosis. This study aims to investigate the biomechanical effects of cervical kyphotic deformity, with a particular focus on the stress and strain variations in facet joints and IVDs, to elucidate the underlying mechanical mechanisms of cervical kyphosis.

A finite element (FE) model of the lordotic cervical C2-C7 motion segment was constructed based on computed tomography (CT) images of a healthy adult. The model was modified to represent three distinct cervical spine alignments: lordotic cervical spine, straightened alignments, and cervical kyphosis. Under physiological loadings conditions, stress and strain were analyzed across these states to assess their biomechanical impact on the facet joints and IVDs.

In a lordotic cervical spine, the highest stress and strain were concentrated at the C3-C4, C4-C5, and C5-C6 facet joints. In contrast, under cervical kyphosis, the C2-C3 and C6-C7 segments demonstrated a substantial increase in stress and strain. Facet joint stresses increased by up to 71.10-fold at C2-C3 and 356.12-fold at C6-C7 compared with the lordotic model. Furthermore, kyphotic alignment elevated IVD stress, which was consistently concentrated in the anterior region of the C2-C3 disc across all loading conditions.

The C2-C3 and C6-C7 segments are subjected to increased mechanical loads in straightened cervical alignment and kyphotic deformity, thereby increasing their susceptibility to facet joint degeneration. Furthermore, cervical kyphosis is associated with accelerated disc degeneration, with stress concentration predominantly occurring in the anterior regions of the discs. These findings provide biomechanical insights into the progression of cervical spinal deformities and may help guide clinical diagnosis and treatment strategies.