The relative influence of vertebral body and intervertebral disc shape on thoracic kyphosis

Objective. The aim of this study was to quantify the morphology or shape of thoracic vertebral bodies and intervertebral discs, and to examine the ex vivo association of thoracic kyphosis with these shape parameters. Design. A quantitative, retrospective study design was applied to define vertebral body and disc influences on thoracic kyphosis. Background. Age-related progression of thoracic kyphosis is a well-defined process that is influenced by the morphology of vertebral bodies. However, little is known about the contribution of intervertebral disc shape to the thoracic curvature. Methods. Vertebral and disc morphology, as represented by antero-posterior height ratios, were quantified in 93 lateral spine radiographs and midsagittal computed tomography films of ex vivo spines. Kyphosis was indicated by the Cobb angle. Linear and stepwise regression were applied to examine relationships for cumulative (T1–T12) and regional (T4–T9) analyses. Results. Vertebral morphology was highly predictive of thoracic curvature, while a poorer association was noted for disc morphology. The combined influence of both accounted for >85% of the variability in kyphosis. There was a trend for a more pronounced anterior wedge configuration of the midthoracic vertebral bodies and discs. Higher associations between variables were also noted in this region. Conclusions. The normal kyphosis of the thoracic spine reflects the morphological adaptation of both the vertebral bodies and intervertebral discs.