Experimental Study On Acute Stretch Injury Of Cervical Spinal Cord In Rabbits

Objective:The incidence of fracture-dislocation in lower cervical spinal increases as a result of increase of various high-energetic trauma. There are provid satisfactory recover enviroment for nervous system by reducing early and relieving compression of spinal nerves. Skull traction reduction under X-ray fluoroscopy monitoring immediately after trauma is generally thought to be an effective and reliable method to treat facet dislocations in lower cervical spine. Overstretching of cervical spinal cord must be averted at closed reduction, because it may cause spinal cord injury as dynamic coup and static compression of spinal cord.In this study, we firstly established an animal model of stretch injury in rabbits, and then we observed the cervical spinal cord blood flow, motor evoked potentials and neuronal cell apoptosis in the early stage after cervical spinal cord's stretch injury.Materials and Methods:Forty-two healthy adult rabbits of either sex were randomly grouped as group A (control, 6 rabbits), group B (in this group, the dislocation distance of the lower facet of the 5^th cervical vertebrae to the upper facet of the 6^th cervical vertebrae was about half of the height of upper facet and lasted for 5 minutes, 12 rabbits), and group C (in this group, the dislocation distance of the lower facet of the 5^th cervical vertebrae to the upper facet of the 6^th cervical vertebrae was more than one time of the height of upper facet and lasted for 5 minutes, 12 rabbits) and group D (in this group, the dislocation distance of the lower facet of the 5^th cervical vertebrae to the upper facet of the 6^th cervical vertebrae was two times of the height of upper facet and lasted for 5 minutes, 12 rabbits). After anesthesia, the anterior longitudinal ligament, intervertebral disc, interspinous ligament, supraspinous ligament, etc between the 5^th and 6^th vertebrae were removed to completely free the intervertebral space and then skull traction was performed with a homemade skull tractor to obtain exact dislocation distance as described above. At different time points, and just before and afterthe traction, the cervical spinal cord blood flow (SCBF), motor evoked potentials (MEP), neuronal cell apoptosis were measured. Also the expression of Bax and Bcl-2 was visualized by immunochemistry and the average optical density of these two proteins was also analyzed. Results:1. With the increase of traction weight employed on the cervical spinal cord, the SCBF of C5,6 decreased gradually, and recovered at different degrees in different groups after traction. Eight hours after traction, the SCBF of group B and group C was not differentiate significantly from that of group A and that of group B and group C before traction (P>0.05). In group D, the SCBF decreased obviously when traction was performed, and 8 hours after traction, the SCBF in this group was significant differentiate from that of group A and that of group D before traction (P <0.05).2. With the increase of traction weight employed on the cervical spinal cord, the amplitude of MEP Nl and PI decreased, the latent time increased, and they all recovered at different degree after the release of traction.3. As the results of pathological experiment showed, with the increase of traction weight employed on the cervical spinal cord, the injured spinal cord displayed ischemic and hypoxic changes at different degrees in different groups.4. With the aggravation of stretch injury, the number of apoptotic cells increased and reached a summit 24h after injury and then decreased gradually 72h after injury. The main type of apoptosis is astrocytes, with little part of them is neurons.5. The expression of apoptosis-associated protein, Bax, enhanced with the aggravation of stretch injury and reached a summit 24h after injury. The expression of Bcl-2 in all the groups was weak and it decreased 8 hours after injury in group D.Conclusions:1. The gradual decrease of SCBF along with the aggravation of stretch injury indicates that the decrease of SCBF is one of the early pathological changes after stretch injury of cervical spinal cord.2. Significant changes of MEP took place after stretch injury, and the changes correlated with the changes of SCBF and pathological changes.3. Apoptosis occurred in the anterior horn of cervical spinal cord, main type of whichis astrocytes and little part of which is neurons. The apoptosis index increased along with aggravation of stretch injury.4. The expression of Bax enhanced along with aggravation of stretch injury, while the expression of antiapoptosis-associated protein, Bcl2, was higher than that of normal control, but decreased with the aggravation of apoptosis.