A review of biomechanics of the central nervous system. Spinal canal deformations due to changes in posture. A hand search of available reference texts and a computer search of literature from the indexed medicus sources were collected with special emphasis placed on spinal canal changes caused by various postural rotations and translations of the skull, thorax, and pelvis. All spinal postures will deform the spinal canal.
Flexion causes a small increase in canal diameter and volume as the vertebral lamina are separated.
Extension causes a small decrease in canal diameter and volume as the vertebral lamina are approximated. Lateral bending and axial rotation cause insignificant changes in spinal canal diameter and volume in cases without stenosis. Rotations of the global postural components, head, thoracic cage, and pelvis cause changes in the diameter of the spinal canal and intervertebral foramen. These changes are generally a reduction of less than 1.5 mm in extension, compared to a small increase in flexion of approximately 1mm. These small changes do not account for the clinical observation of patients having increased neurological signs and symptoms in flexion.