In vivo effects of axial loading on healthy, adolescent spines.

Five healthy adolescents were studied using a three-dimensional radiographic technique to analyze the in vivo effects of standing, supine and supine Cotrel traction positioning on the orientation of spinal segments. In general the configuration of these spines was found to be relatively unaffected by changes in subject position and column loading. The major effects of supine positioning appeared to be lessening of standing lumbar lordosis while supine traction tended to diminish this effect. Measurement of rotation relative to a common reference body, L4, was influenced by the degree of AP and ML wedging throughout the column. The standing curve was found to be slightly rotated by a small but constant amount at each level and tended to derotate as a whole with supine and supine traction positioning. Measurement of successive intervertebral rotation showed effects independent of wedging with each vertebral body randomly rotated and unaffected by subject orientation. With the exception of central vertebral disk heights, all parameters measured possessed relatively wide limits of variability which appeared to be the result of true intersubject scatter as opposed to measurement error.