Vertebral column development and its relation to adult pathology.

Normal notochordal and vascular attrition leaves weak spots in intervertebral discs through which intravertebral prolapse of disc material frequently occurs. Some varieties of prolapse cause somatic spinal pain. Asym-metrical and asynchronous growth of normal vertebral arches rotates thoracic vertebral bodies slightly to the left in infants and to the right in adolescents. Primary vascular asymmetry could cause the observed vertebral asymmetry. Luschka's joints develop in the cervical spine during childhood and give some protection against postero-lateral disc prolapse, but cervical zygapophyseal joints give little protection to the disc in sagittal plane movements. The lumbar zygapophyseal joint plane changes from a coronal orientation in infants to a biplanar coronal and sagittal orientation in adults, which enables the joints to restrain both rotation and excessive flexion. This explains the observed pattern of stress related age changes in the joints.