Radiological pathogenesis of cervical myelopathy in 60 consecutive patients with cervical ossification of the posterior longitudinal ligament

Study design: The radiological pathogenetic factors for cervical myelopathy in 60 consecutive patients with cervical ossification of the posterior longitudinal ligament (OPLL) were investigated retrospectively. Objective: To clarify which patients with OPLL will develop cervical myelopathy. Methods: Sixty consecutive patients with OPLL were radiologically assessed comparing the myelopathic patient group (M group, n=41) and the mild or non-myelopathic patient group (non-M group, n=19). Results: The narrowing ratio of the spinal canal in the M group (47.1%) was significantly greater (P=0.026) than that in the non-M group (38.3%). The two groups showed a significant difference (P=0.0016) with regard to the Pavlov ratio (M group, 0.73; non-M group, 0.84). The total range of motion of the cervical spine did not differ between the two groups but the per cent range of motion was significantly greater (P=0.037) in the M group than in the non-M group. Conclusion: This study suggests that factors important in the onset or aggravation of myelopathy are factors related to pathological compression by OPLL, cervical soft disc herniation, developmentally narrow spinal canal, and local or non-proportional hypermobility.