Effect of long-term axial spinal unloading on vertebral body height in adult thoracolumbar spine.

The human spine is influenced by mechanical loads. To our knowledge, this is the first study to assess the effect of long-term axial unloading on morphology of healthy vertebras in adults. The objective of this study is to quantify the effects of long-term relative axial unloading on thoracolumbar vertebral body height in adults. In this study, 218 vertebras on 200 plain lateral radiograms of patients with thoracolumbar vertebral body fracture, which underwent long segment instrumentation and fusion and had a relative axial unloading on five vertebrae of thoracolumbar spine were evaluated. Anterior vertebral body height (AVBH) and posterior vertebral body height (PVBH) proximal and distal to the fractured vertebrae were measured before and at least 1 year after the unloading operative procedures. AVBH of the first distal adjacent vertebrae and summative AVBHs of the first distal and proximal adjacent vertebras to the fractured vertebrae were significantly increased after 1 year of unloading, whereas the PVBH changes were not noticeable and the mean of cumulative height of two levels of proximal and distal adjacent vertebras to the fractured vertebrae did not show significant difference. Vertebral body height of lumbar was more influenced by unloading when compared with thoracic spine. Long-term relative axial unloading can affect the height of healthy vertebral bodies in adult spine.