An experimental study on the influence of spinal shortening on the spinal cord

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Spinal column shortening is one of the effective modality in reconstruction of total spondylectomy. We studied morphometric and physiologic changes of the spinal cord in spinal column shortening using animal models.[Methods] Total spondylectomy of T12 was performed after 2 above and 2 below spinal instrumentation in 16 dogs. Spinal column was gradually shortened until the lower endplate of the T11 contacted onto the L1 upper endplate (maximum of 20 mm).[Results] The dural sac and the spinal cord did not change their shapes until 8 mm (44%) shortening. From 8 mm to 11.5 mm (64%) shortening, the dural sac was deformed like an accordion while the spinal cord maintained its shape. In more than 11.5 mm shortening, the dural sac buckled and became like spanworm, and the spinal cord was compressed by the buckled dura in its concave side. In the spinal cord evoked potentials study, no significant changes could be seen until 11.5 mm shortening, but augmentation of amplitude was recorded at more than 11.5 mm shortening. At 20 mm (100%) shortening, positive going potentials were seen at the level of upper endplate of the L1 vertebra.[Conclusion] The morphometric change of the spinal cord and the dural sac in association with spinal column shortening can be characterized in three phases ; (phase 1) no deformity of the dural sac and the spinal cord, (phase 2) shrinking and buckling of the dural sac, (phase 3) spinal cord deformity and compression by the buckled dura. The phase 1 is the safety range of for the spinal cord. The phase 2 is the warning range, and the phase 3 is the critical range.