| Traumatic atlantoaxial instability refers to excessive or abnormal activity of atlantoaxial joint under physiological load after being injured. It is not uncommon, accounting for about50%of the cervical spine trauma, with odontoid fracture as a common cause. If aggravated, it can cause anterior or posterior dislocation, which often combine with spinal cord and nerve root compression and stimulation and could even be life-threatening.Looking for a good spinal cord compression animal model induced by atlantoaxial instability has important meaning in order to record pathological characteristics of spinal cord injury and neural function qualitatively and quantitatively and to explore correlation between them. Therefore, we designed partial spinal cord injury model with atlantoaxial dislocation in rabbits, and observed hindlimb motor function and early pathologic changes of spinal cord dynamically, in order to provide a theoretical basis for clinical prevention and therapy of spinal cord injury induced by atlantoaxial instability.Experiment1Establishing partial spinal cord injury model with atlantoaxial in rabbits Objective To establish partial spinal cord injury model with atlantoaxial dislocation in rabbits by surgical operation.Methods16Japanese big ear rabbits were randomly divided into2groups:model group (group A), sham operation group (group B), each group of8, and were intraperitoneally anaesthetized with10%chloral hydrate (dose3-5ml/kg). Do skin preparation for rabbits in group A after anesthesia with C2as centre. Fix the rabbits supine on rabbit bench, do a incision about4cm in length right to the trachea with C2as centre in order to reveal the atlantoaxial front. Cut odontoid basal with scissors, release and separate atlantoaxial lateral joint capsule carefully. And anterior operation were done. Lie the rabbit prostrate on bench using custom-made gypsum and do a median incision on posterior neck with C2as centre in order to reveal C1side, spinous process of C2and C3.Cut connecting tissue of Cl and C2, causing in atlantoaxial instability. Anteflect and compress the atlas gradually under CSEP monitoring until evoked potential amplitude declined50%. Fix spinous process of C2and C1side with2titanium Kirschner pins. And Partial spinal cord injury model with atlantoaxial in rabbits were established. Only do incision, exposure and suture of neck skin for group B without causing spinal cord injury. And the incision length and position were the same as experimental group. Group B were CSEP monitored to exclude the consequence of anesthesia and operation on evoked potentials. Each group were examined by X-ray, CT three-dimensional reconstruction preoperative and postoperative. And the spinal canal compression ratio were calculated (spinal canal compression ratio=(preoperative spinal anteroposterior diameter postoperative spinal anteroposterior diameter)/preoperative spinal anteroposterior diameter x100%). Execute animal with excessive anesthesia method, take spinal specimens1.5cm in length, observe histological changes of spinal cord under light and electron microscopic. Results Evoked potential changes had no statistical significance within90minutes of the application of chloral hydrate anesthesia, before and after operation, and between two groups. Odontoid process base fracture, atlantoaxial dislocation,2titanium Kirschner pins could be observed through image examination in group A.The average spinal canal compression ratio was about37%. Postoperative histopathological examination:light micro scopy revealed that gray matter had small amount of bleeding lesions, gray and white matter had visible mild edema in model group. Electron microscope showed the neuron cell body were basically normal, myelin and axonal gap increased. Spinal neural structure were normal in sham operation group.Conclusion Partial spinal cord injury model with atlantoaxial dislocation in rabbits could be established by surgical operation successfully. Effect of anesthesia and operation on evoked potential changes were not found.Experiment Two Dynamic observation on early pathological changes of partial spinal cord injury model with atlantoaxial dislocation in rabbitsObjective To observe hindlimb motor function and early pathologic changes of spinal cord dynamically, in order to provide a theoretical basis for clinical prevention and therapy.Methods32rabbits were randomly divided into4groups:6h post spinal cord injury group(group A),24h post spinal cord injury group (group B),72h post spinal cord injury group (group C), sham operation group (group D),method of establishing model was the same with Experimental One. Examination of X-ray, CT three-dimensional reconstruction were done before and after operation. Do fluid infusion intraoperative and postoperative with penicillin800000units and dexamethasone10mg via intravenous drip. Do muscle injection with800000units of penicillin sodium on the third day after operation. Keep rabbits warm after they were awake and squeez urine each8h. Observe hindlimb motor function before execution. Execute animal6h,24h,72h post-operation and take spinal cord specimens. Observe under light and electron microscope after HE staining, Tunel staining.Results Image examination showed odontoid process base fracture, atlantoaxial anterior dislocation in model groups, with spinal cord compression ratio of36%averagely.1group A:The animal model had varying degrees of motor dysfunction6h post operation,87.5%scored3-4by modified Tarlov’s rating. histological examination: Gray matter hemorrhage, slight neuron vacuolar degeneration, white matter edema, mild cavernous transformation, no obvious neuronal necrosis were observed under the light microscope, HE staining. Tunel staining showed positive neurons, glial cells expressed large amounts of positive particles, nuclei pyknosis, irregular shape, brown granules scattered in nucleus, apoptotic body, owl’s eye. Myelinated nerve fiber myelin swelling, serious separation, myelin fracture, unmyelinated nerve fiber myelin disappearance were observed under electron microscope. Axons did not change significantly.2group B:87.5%scored2-3by improved Tarlov’ s rating24h postoperative. Histological examination:under the light microscope, HE staining showed large gray hemorrhage and affected white matter, white matter demyelination cavernous, neurons shrinkage, triangular. Tunel staining showed positive neurons, glial cells expressed large amounts of positive particles, which increased compared with group A, but no obvious change of appearance. Under electron microscope, obvious myelin swelling, fracture and stratification, visible edematous entrapment of axons, nerve structure of axon disappeared, formation of irregular blank point and the blank area. 3group C:the score of improved Tarlov’s rating continued to decline, located in2-3. Histological examination:under the light microscope, HE staining showed neurons shrinkage, triangular in shape, damage of large gray area, absorption of bleeding area, proliferation of phagocytic cells and glial cells. Tunel staining showed positive neurons, glial cells, expression of particles is still obvious, declined compared with group D. under electron microscope, myelin delamination and fracture of myelinated nerve fiber were observed, not significantly different than group D.4sham operation group (group D):double lower limbs motor function of rabbits recovered to normal after awake and scored5by the improved Tarlov’s rating. Under light microscopy, electron microscopy, spinal nerve structures were normal, Tunel staining showed positive particles.Conclusion when atlantoaxial were fixed (not relocated), clinical impairment of nerve function aggravates gradually in partial spinal cord injury model with atlantoaxial dislocation. Widespread neuronal apoptosis were observed6h post-operation, reached the peak24h post-operation, and continued until72h post-operation. |
PDF Full Text Request