Position of axis for rotation at the intervertebral joint in rats

To elucidate whether the position of axis for rotation at the intervertebral joint is related to the spinal curvature, the authors investigated the spinal columns of rats. The spinal column of the rat was composed of 7 cervical, 13 thoracic, 6 lumbar, 4 sacral, and 27 coccygeal vertebrae. It was observed that the position of axis for rotation at the intervertebral joint was shifted on the superior and inferior views of the 2nd thoracic vertebra and was next shifted on the superior and inferior views of the 10th thoracic vertebra. X-ray examination demonstrated that lordosis was seen in the cervical and lower lumbar (L4-L6) spine, whereas kyphosis was seen in the thoracic and upper lumbar (L1-L3) spine. The present study did not support the possibility that the position of axis for rotation at the intervertebral joint was dorsal in the spinal site of lordosis, whereas it was ventral in the spinal site of kyphosis.