[[Studies of Ossification of the posterior longitudinal ligament in the cervical spine using microradiography and histochemistry (author's transl)].

ossification of the posterior longitudinal ligament (OPLL) is seen by X-ray as a condition which shows a heterotopically formed bony shadow at the posterior part of vertebral bodies of the cervical spine. OPLL causing severe myelopathy is called a Japanese disease. Recently, it has been shown that this condition is not only seen in Japan, but also in other countries especially in Asia. In order to obtain information of pathogenesis of this condition, the present author carried out histochemical investigations on 2 autopsy cases which had been treated as OPLL myelopathy, and 12 surgical materials. Totally 30 spinal vertebrae were examined. They were prepared for study with undemineralized ground sections mainly. The following results were obtained. 1) Microradiography revealed that the calcified tissue on the ligament had two marked structures, one was highly calcified tissue, and the other was bony tissue with lower density. 2) Most of the highly calcified tissue with variable distribution ranging from a sparse to a dense one contained round radiolucent spots probably consisting of cartilage-like cells. This type of calcified tissue is accompanied by the organic matrix, which was stainable with van Gieson stain, PAS reaction, Alcian blue stain and toluidin blue metachromasia. 3) A part of highly calcified tissue showed linearly distributed pattern without radiolucent round spots. This type of calcified tissue was also stained with van Gieson stain and PAS reaction. However, this organic matrix was not accompanied by marked reaction of acid mucopolysaccharides. 4) No essential histochemical difference was found between the highly calcified tissue on the ligament and other various types of heterotopically formed calcified tissue. 5) Microradiography revealed the remnant of resorption process at the boundary between the highly calcified tissue and the bony tissue. This finding of the resorption lacunae indicated that the highly calcified tissue was formed initially, followed by bone tissue formation. The process of internal remodeling was also observed in the bony tissue. 6) The distribution of the highly calcified tissue, bony tissue and resorption cavities indicated several patterns of remodeling process which was characterized by the new bone formation at the region near the vertebral body. These characteristics were apparently due to the mechanical stresses acting on this bony structures, as seen in some other heterotopic bone formations such as the healing process of fracture or tooth extraction socket.