Pathogenesis of myelopathy in patients with ossification of the posterior longitudinal ligament

Object. The goal of this study was to clarify, the pathogenesis or myelopathy in patients with us ossification of the posterior longitudinal ligament (OPLL) based on the relationship between static compression factors and dynamic factors. Methods. There was a total of 247 patients. including 167 patients who ere conservatively followed for a mean of II years and 2 months and 80 patients who had myelopathy at initial consultation and underwent surgery. The changes in cUnical symptoms associated with OPLL in the cervical spine were examined periodically. During the natural course of OPLL in the cervical spine, 37 (22%) of 167 patient,, developed or suffered aggravated spinal symptoms. All of the patients with a space available for the spinal cord (SAC) less than 6 min suffered myelopathy, whereas the patients with an SAC diameter of 14 min or greater did not. No correlation as found between the presence or absence of myelopathy in patients whose SAC diameter ranged from 6 mm to less than 14 mm. In patients with myelopathy hose minimal SAC diameter ranged from 6 mm to less than 14 mm. the range of motion of the cervical spine was significantly greater. Conclusions. These results indicate that pathological compression by the ossified ligament above a certain critical point may be the most significant factor in inducing myelopathy, whereas below that point dynamic Factors may be largely involved in inducing myelopathy.