To analyze the mechanism of chronic compression myelopathy in human spondylosis, ossification of ligaments, and spinal cord tumors, we tried to make a spinal cord continuous compression model in rats using uterine-cervical dilator Dilapan, which has the character of slow expanding, as compression-materials and investigated the lesions. The spine was pressured continuously with compression-material in the sublaminal epidural space at Th9 vertebral level for 1,2,3,7,14,30 and 90 days. The model was investigated morphologically, by histochemistry, immunohistochemistry, electron microscopy as well as conventional histology. The morphological data were analyzed quantiatively by morphometries.
In this model, Dilapan occupied 24.2% of spinal canal in the cross sections. All rats transiently became spastic paraplegia after the placement of compression-materials, but the palsy was recovered in 80% of the rats. Histologically, at the 1st day, hemorrhagic necrosis of the spinal cord occurred, whic
h was mostly localized in the pressured sites, i.e.posterior column. In the white matter, a spongy change appeared at 2nd day and lasted until 90th day. The spongy change was not localized at the compression site but distributed diffusely in the white matter of spinal cord, although the change was stronger in deeper parts of white matter than in superficial ones. Histochemistry and immunohistochemistry disclosed that the spongy change of white matter was associated with decrease of axon and neurofilaments, but not with demyelination. Examination of toluidine blue staining of thin sections and electron microscopy demonstrated that main change occurred in the lateral column was the degeneration of axon of myelinated fibers, such as edematous swelling, loss of axon causing myelin-tangles, and detachment from myelin sheath. These axonopathy had been continuously seen as long as 90th day. Changes of myelin, such as fragmentation, splitting, and thinning, were also seen in the lateral column but the frequency was low. Morphometry of diameters of myelinated fibers and thickness of myelin did not indicate any significant change of myelin. Furthermore, release of compression decreased the number of degenerated axons. These findings showed that continuous spinal cord compression model using Dilapan is suitable for the analysis of chronic compression myelopathy, indicating that axonopathy but demyelination may be one of the main changes in chronic compression myelopathy.