Dynamic changes in spinal cord compression by cervical ossification of the posterior longitudinal ligament evaluated by kinematic computed tomography myelography.

STUDY DESIGN: A prospective clinical study. OBJECTIVE: To investigate the dynamic causative factor in the pathogenesis of myelopathy in patients with cervical ossification of the posterior longitudinal ligament (OPLL) using kinematic computed tomography (CT) myelography. SUMMARY OF BACKGROUND DATA: Kinematic CT myelography is useful for dynamically evaluating the cervical spine with high-resolution images, particularly in bony compressive lesions. However, no studies have evaluated the dynamic factors in patients with OPLL using kinematic CT myelography. METHODS: From 2008 to 2013, 51 consecutive patients with OPLL who presented with myelopathy were prospectively enrolled in this study. The patients were examined with kinematic (flexion-extension) CT myelography using a multidetector CT scanner. The range of motion at C2-C7 from flexion to extension was measured in the sagittal view. The segmental range of motion, anterior-posterior diameter and cross-sectional area (CSA) of the spinal cord were measured at the level where the spinal cord was most compressed by OPLL. RESULTS: The neurological condition of the patients evaluated by Japanese Orthopaedic Association scores were 10.8 ± 2.4 points. The mean range of motion at C2-C7 and at the most compressed segment were 23.1 ± 11.7 and 7.0 ± 4.4°, respectively. Both the anterior-posterior diameter and the CSA at the most compressed levels were significantly decreased during neck extension compared with flexion. Interestingly, the anterior-posterior diameter and the CSA were decreased during neck flexion in 13.7% (7/51) of the patients. All 7 of these patients had massive OPLL with an occupying rate 60% or more. The dynamic change rate of CSA (flexion/extension) was significantly smaller in patients with an OPLL occupying rate 60% or more compared with patients with an occupying rate less than 60%. CONCLUSION: Although spinal cord compression was increased during neck extension in most of the patients, greater levels of compression could be placed on the spinal cord during neck flexion when the patients had OPLL with a high occupying rate. LEVEL OF EVIDENCE: 4.