Histopathologic and morphometric study of spinal cord lesion in a chronic cord compression model using bone morphogenetic protein in rabbits.

Chronic compressive myelopathy was induced in domestic rabbits by implanting bone morphogenetic protein on the ligamentum flavum of the lumbar spine, and the resulting spinal cord lesion was studied histopathologically. In addition, morphometry of myelinated nerve fibers of the white matter in the pathologic specimens was performed to elucidate the mechanisms of cord injury. No loss of white matter nerve fibers was seen when the cord compression ratio (sagittal diameter/transverse diameter) was > 45%, although 6 months later myelin thinning was present throughout the white matter. When the cord compression ratio was < or = 45%, loss of fibers, particularly of large fibers, was seen in the superficial layer of the white matter, with the nerve fibers remaining after 6 months showing decreased diameters. No motor paresis was evident in any animal. These histologic changes represent the early pathologic condition induced by chronic cord compression.