A review of biomechanics of the central nervous system - Part I: Spinal canal deformations resulting from changes in posture

Objective: To discuss how the spinal cord deforms as a result of changes in posture or biomechanical alterations of the spine. Data Collection: A hand search of available reference texts and a computer search of literature from the Index Medicus sources were collected, with sp ecial emphasis placed on spinal canal changes caused by various postural ro tations and translations of the skull, thorax, and pelvis. Results: All spinal postures will deform the spinal canal. Flexion causes a small increase in canal diameter and volume as the vertebral lamina are se parated. Extension causes a small de-crease 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 wi thout stenosis. Conclusions: Rotations of the global postural components, head, thoracic ca ge, and pelvis cause changes in the diameter of the spinal canal and interv ertebral foramen. These changes are generally a reduction of less than 1.5 mm in extension, compared with a small increase in flexion of approximately 1 mm. These small changes do not account for the clinical observation of p atients having increased neurologic signs and symptoms in flexion.