Ossification in the region of the posterior longitudinal ligament as a cause of cervical myelopathy.

In 1967, we operated on a patient for cervical cord compression caused by an unusual type of ectopic bone formation in the spinal canal which we tentatively identified as ossification within the posterior longitudinal ligament. Until that time we had believed that calcification of the vertebral ligaments is a phenomenon secondary to spondylosis (Oppenheimer, 1942) and does not cause symptoms by itself. However, about the same time, a description of no less than 18 similar cases was published by Onji, Akiyama, Shimomura, Ono, Hukuda, and Mizuno (1967). Additional cases were also found in Japan (Yokoi, 1963). It seems, therefore, that these cases, while probably rare, constitute a distinct pathological entity. Although calcification and ectopic bone formation have been described before in various ligaments of the spine (Oppenheimer, 1942; Cloward, 1967), they were found accidentally without giving rise to clinical symptoms. A search for similar cases was undertaken and six additional patients with such abnormalities were found.