Experiment Studies On The Corelation Of The Function And Decompression Time In The Cervical Spinal Cord Under Anterior And Posterior Stabilizing Mechanical Compression

With the development of aging population , CSM (cervical spondylotic myelopathy) has been one of the common diseases to affect the old people's health. CSM is a kind of degeneration diseases in cervical spinal, which is encountered a series of myelopathy for spinal cord nerve cells or its blood vessls compressed by cervical disc herniation , spinal cord stenosis , ossification of the posterior longitudinal ligament(OPLL) and so on.Various animal experiments on spinal cord injury have been conducted in order to deepen the understanding on the pathology of compressed lesions. However, these experiments usually utilized the models of acute symptoms produced by weight bearing and/or clamps , and these have been a few studies on chronic compression. Major symptom of cervical spondylotic myelopathy is spinal paralysis which is generated by the osteoarthropathic changes of the spine , and the spine presents such morphological characteristics as cervical disk degeneration, osteophyte formation, hypertrophic yellow ligament, cervical spinal stenosis, and abnormal mobility of the cervical spine, in regard to the generation process of cord symptoms , there have been two major assumptions . one emphasizes tissue damages caused by mechanical compression given to the spinal cord , and the other one proposed a combination of these two hypothesis . However pathology of myelopathy has remained unclear because of the absence of an appropriate animal model for the studies. Objective:In this study, we tried to establish a goat model with typical clinical characteristics of cervical compressive myelopathy, in which disk and facet were maintained in order to preserve mobility of the cervical spine , and compression was given to a single intervertebral space using a Titan screw from the front produced and a Ti plate from the dorsal side. In this model, spinal cord compression is produced when the cervical spine moves. With MRI, electrophysiological test, and histological examination and nerve cells apoptosis observed, we confirmed that this model efficiently produces delayed myelopathy. Materials and methods:Twenty 20-24 month old goats (body weights: 13-17 kg, mean: 15 kg) were divided into three groups in this study: control group(n=4) , compression 3 months(n=8) and 6 months (n=8)group, and every compression group was divided into decompression 1 month(n=4)and 3 month group(n=4). All animals were given an ordinary diet and water. Surgery was performed under the i.v. anesthesia using 40 mg/kg of pentobarbital sodium. All compression group animals underwent cervical cord compression produced by anterior Titan screw and posterior plate implanted. An X-ray film of the cervical spine was taken intraoperatively to ascertain the pressure level and depth of screw . A hole was produced slightly below the center of the C5 vertebral body by using an electric drill with a bur ( 6mm in diameter), its depth was measured with a micrometer, a Titan screw ( 6mm in diameter , 1mm of pitch) was placed into the hole at a rate of Imm/min to produce approximately 3-4 mm compression measured from the posterior side of the vertebral body. This was determined as anterior compression. During the surgery , electrophysiological monitoring of the spinal cord was conducted, and no changes in wave patterns were confirmed. After the surgery , antibiotics were i.v. administered. In the following days , walking pattern was monitored , and no paralysis was confirmed. Two weeks after anterior compression, the goats were anesthetized in the same manner , a longitudinal incision was made on the back centered on the spinous process of the fifth cervical spine and the paravertebral muscles were stripped from the spinous process. The spinous process of the sixth cervical spine was resected , the vertebralarch was slightly shaved . the yellow ligament between the vertebral arch of C5 and C6 was resected , and then a Ti plate (12mm height 6mm width 1mm thickness) was inserted horizontally below the arch of C5 to produce posterior compression. Before and during this s...