[Experimental study on the spinal lesions in hyperostotic mouse (twy/twy): special reference to the pathogenesis of the ossification of the spinal ligaments and to the action of ethane-1-hydroxy-1, 1-diphosphonate (EHDP)].

The hyperostotic changes in the spine of the twy mouse and the action of ethane-1-hydroxy-1, 1-diphosphonate (EHDP) on those hyperostotic changes were studied histomorphometrically. The periosteal bone formation and the endosteal bone resorption in the anterior cortex of the vertebral bodies of the twy mouse continued even after maturation, resulting in the anterior cortex shifting to the anterior direction. In parallel with these changes, calcification in the enthesis (to which spinal ligaments and the outer layer of disc fibrosis are attached) continued, ending in ankylosis of the whole spine. It was similar to a membranous ossification. Moreover calcification in these regions was most sensitively inhibited by EHDP and reappeared as soon as the discontinuation of EHDP. These findings showed that the pathogenesis of the twy mouse was the hyperostosis which continued even after maturation in the genetical region of a membranous ossification, especially in the enthesis. Further they appeared to be similar to the initial changes in ankylosing spinal hyperostosis or the ossification of the spinal ligaments. In addition, our results provided evidence for the usefulness of EHDP in the twy mouse.