The effects of intervertebral fusion in patients with myelopathy due to ossification of the posterior longitudinal ligament of the cervical spine.

Fifty patients with ossification of the posterior longitudinal ligament of the cervical spine were treated by anterior intervertebral body fusion and compared with 30 other patients treated conservatively. We found that patients with narrowing of the cervical canal to 0.5 of the normal diameter were improved by simple intervertebral fusion without excision of the ossified ligament. Patients with more extensive ossification and narrowing of the spinal canal to less than 0.4 of the normal diameter might have either severe symptoms or unexpectedly minor symptoms and the latter were attributed to the spontaneous fusion and loss of mobility that had occurred. Conversely, patients with less severe ossification but abnormally increased intervertebral mobility often had severe symptoms but were greatly improved following intervertebral fusion. It was concluded that narrowing of the spinal canal in the presence of mobility of the neck produced unfavourable dynamic compression of the spinal cord and that reduction in the mobility of the spine was effective in reversing many of the signs of cervical myelopathy.