The etiology of ossification of the spinal ligaments remains obsure. We selected the ossification of the supraspinous ligament (OSSL) as a method to clarify the etiology of ossification.
We perform to calculate the stress on the supraspinous ligament and to discuss causative factors of ossification of the spinal ligaments from the view point of the local mechanical factors.
OSSL can be divided into three types (type I, type II and type III) according to the shape and the size.
The subject of our study are 30 cases with type I, 20 cases with type II, 20 cases with type III and 30 normal persons as a contrpl.
The following results are obtained:
1) stress on the supraspinous ligament mainly depends on the body weight and the distance from the center of gravity to the center of the intervertebral disc,
2) in type II and type III of the ossification, the apex of thoracic kyphosis is chiefly seen at the Th7 and Th8, but biggest ossification is almost always found at Th11 and Th12,
3) in type III, thoracolumbar kyphosis (T10-L2) is increased and lumbar lordosis (L1-L5) is decreased, and
4) OSSL has more relation to general factors than local factors.
