In ossification of the posterior longitudinal ligaments (OPLL), axonal disruption results in motor and sensory function impairment. Twy (tiptoe-walking Yoshimura) mice develop spontaneous calcification in the cervical ligaments, thereby causing chronic compression of the spinal cords. To determine whether in vivo diffusion tensor tractography (DTT) can evaluate the axonal disruption of the chronic compressive spinal cords in twy mice, 6-, 15-, and 20-week-old twy mice were chronologically subjected to DTT. MRI was performed using a 7.0-Tesla magnet with a surface coil (CryoProbe). Diffusion tensor images were analyzed using TrackVis (Massachusetts General Hospital, MA, USA). We succeeded in depicting in vivo high-resolution DTT of the twy mice. The progress of the ligamentous calcification was observed at C2-3 level in each twy mouse, and the number of RT-97 or SMI31 positive fibers was decreased depending on the severity of the compression of the spinal cord. Quantitative analysis of sequential DTT enabled to detect subtle damage of the compressed spinal cord prior to the deterioration of neurological function in twy mice. Thus, in a clinical setting, DTT could be a new effective imaging modality in patients with cervical OPLL.
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