Analysis of preexistent vertebral rotation in the normal quadruped spine.

STUDY DESIGN

In this CT study, vertebral rotation was analyzed in the transverse plane of the normal, nonscoliotic canine spine with a computer-based measurement method.

OBJECTIVES

To determine if a rotational pattern exists in the normal, nonscoliotic quadruped spine, similar to what is seen in humans.

SUMMARY OF BACKGROUND DATA

Idiopathic scoliosis does not occur in quadrupeds. In humans, the normal, nonscoliotic spine shows a preexistent pattern of vertebral rotation, which corresponds to the most prevalent curve types of idiopathic scoliosis. Since this rotational tendency has only been demonstrated in humans, it is not clear if it can be considered as a part of the pathogenesis of idiopathic scoliosis or as a normal anatomic feature.

METHODS

CT scans of the thorax of 42 dogs without clinical or radiologic evidence of scoliosis were used to measure axial vertebral rotation from T1-T13 with a previously developed computer-based CT measurement method.

RESULTS

The results of this study demonstrated a predominant rotation to the right of the upper, mid, and lower thoracic vertebrae of the normal canine spine. The mean vertebral rotation angles differed significantly from zero degrees rotation at level T1, from level T4-T7, and from T11-T13.

CONCLUSIONS

The normal spine of quadrupeds shows rotation of the thoracic vertebrae with a preferred direction to the right, similar to what is seen in humans. Since idiopathic scoliosis does not exist in quadrupeds, this preexistent rotation seems to be a physiologic process in normal spinal development, independent of the pathogenesis of scoliosis.