Upper cervical cord compression due to a C-1 posterior arch in a patient with ossification of the posterior longitudinal ligament and a kyphotic cervical spine in the protruded-head position

In this paper the authors report the case of a patient with ossification of the posterior longitudinal ligament (OPLL) below the axial vertebra (C-2) at the kyphotic cervical spine, with an atlas vertebra (C-1) posterior arch that compressed the spinal cord with the head in a pathognomonic position, similar to a protruded position. This condition appears to be very rare. The morphological findings between the kyphotic cervical spine and OPLL, the upper occipitocervical junction, and the protruded-head position are discussed. A 40-year-old man presented with severe pain radiating to both legs when he yawned, sneezed, or extended his jaw (a protruded-head position). A kyphotic cervical spine with OPLL below C-2 was observed using CT and radiography, yet sagittal T2-weighted MRI failed to identify abnormal findings in a neutral or extension position, except for a slight cervical canal stenosis. However, in a pathognomonic protruded-head position, sagittal T2-weighted MRI showed a C-1 posterior arch that severely compressed the spinal cord at the upper cervical level. Therefore, the authors believe that the severe pain radiating to both legs was caused by a spinal canal stenosis due to a C-1 posterior arch impingement. The C-1 posterior arch was resected, and after the surgery, the patient indicated that the intolerable pain had disappeared. In conclusion, in patients with OPLL and a kyphotic cervical spine, the authors propose that the pathognomonic protruded position is valuable for estimating disrupted compensatory mechanisms at the upper cervical junction.