Experimental Study On Spinal Cord Injury Caused By Vertical Compression Of Vertebral Osteotomy

Objective: Vertebral osteotomy has been proved to be an effective procedure in spinal deformity ; however, there are some dangerous complications , such as spinal cord injury. Fixed by dual nerve roots and ligaments on both sides , spinal cord can be damaged from inevitable shortening with vertebral body osteotomy, which might lead to paraplegia. During the past years , lots of new techniques have emerged in monitoring the function of spinal cord intra-operation ,such as motor potential signal monitoring and ultrasound detecting spinal cord blood supply. This research has been trying to establish a mammal model to test the safety range of vertebral osteotomy .Methods: 10 adult goats were selected for (male and female, weight 32-36KG) the establishment of vertebral osteotomy longitudinal compression shortening animal model. Preoperative intravenous infusion and arterial puncture has been done to monitor the average arterial pressure. Anesthesia induction, tracheal intubation general anesthesia, intravenous propofol (20-25mg / kg) for anesthesia. The goat was fixed on the surgical operation table, and the spinal cord monitoring electrode was placed. The stimulation electrode needle was placed in the motor cortex area of skull; and the needle-shaped recording electrode was placed on the gastrocnemius muscle of the hind limbs on both sides. The reference electrode was placed under the corresponding neck subcutaneous . Sub-magnetic stimulation induced by the composite muscle action potential, before the start of surgery, determine of double hind limb gastrocnemius MEP to establish the baseline. Surgery procedure included pedicle screw fixation from T10-T13, and vertebral osteotomy at T11 and T12, and then longitudinal compression was done by pedicle screws and rods (figure 1). The MEP was monitored again after the decompression of spinal cord (before osteotomy),and the blood flow of the spinal cord was measured by laser Doppler flowmeter.Blood flow (osteotomy shortening of the spinal cord blood flow); ring spinal cord osteotomy during the monitoring of spinal cord MEP, to prevent intraoperative spinal cord injury, affecting the experimental results. After the completion of the osteotomy, measure the distance between T10 / 13, monitor spinal cord MEP and spinal cord blood flow.In this research, five stages were recorded , and the experimental data were put in record in each phase. The specific steps were as followsPhase 1: After the completion of osteotomy, through the pedicle screws and bilateral rods,we hold the device for longitudinal compression shortening, monitoring MEP,until the MEP amplitude dropped to 50% -75% of the baseline, then do the measurement of shortening Distance and SCBF.Phase 2: Continue the vertical compression shortening to measure the shortening distance and SCBF when the MEP amplitude decreased by> 75%.No. 3: continue to vertical compression shortening, to MEP amplitude dropped to 0,do the measurement of short distance and SCBF.Phase 4: during the period of MEP amplitude completely disappeared within 0.5h, in every 10 minutes, measuring the MEP and SCBF, to observe any possible change.Phase 5: during the period of MEP amplitude disappeared completely 0.5h, undo the shortening,and in every 10min, measuring MEP and CBF, to catch any possible changes in MEP and SCBF.At the end of the operation, biopsy of the spinal cord were done. The HE staining was observed under light microscope. The histological changes were observed by electron microscopy.The data were analyzed, and the effect of shortening distance of vertebral osteotomy on MEP and SCBF was clarified, and the safety range of shortening distance of vertebral osteotomy was determined.Result:Phase 1: The shortening distance was 70.1%±5.8% of the T10 /11,84.2% ± 4.3% of the average height of the thoracic and lumbar vertebral when the osteotomy was shortened to 50% -75% . It can be considered that as the osteotomy shortening distance is less than 70% of the height of the vertebral body, less than the average height of thoracolumbar vertebrae 85%, it will not lead to spinal cord injury.There was no significant difference in statistic between SCBF.Phase 2: When MEP decreased> 75% (incomplete spinal cord injury), shortening distance of T10 / 11 usually averaged heights of 82.8% ± 5.4% of vertebral height and 99.5% of height of the thoracic and 6.5% of lumbar spine .It seems that when the osteotomy shortening distance is equivalent to osteotomy at the vertebral height of 80% and the average height of thoracolumbar spine, there may be incomplete spinal cord injury.Meanwhile, SCBF was significantly decreased and decreased to 43.6% ±7.1%of normal blood flow.Phase 3: when MEP dropped to 0 (complete spinal cord injury), shortening distance of T10 /11 averaged 101.7% ± 2.9% of thoracic vertebral height,and the average 122.6% ± 9.3% of height of thoracolumbar spine .It can be concluded that when the osteotomy shortening distance is equivalent to osteotomy at the height of the vertebral body and the average height of 120% of thoracolumbar spine, there may be complete spinal cord injury.During this period, SCBF was further decreased and decreased to 58.4% ± 8.4%of normal blood flow.Phase 4: When the MEP amplitude has been down to 0 within 0.5h, no change of MEP were caught.This period of SCBF continued to decline, and normal SCBF and MEP positive(MEP decreased> 75%, incomplete spinal cord injury) compared to SCBF, were significantly decreased. At 10 min, 20 min and 30 min, MEP was decreased to 66.1 %±6.0%, 69.0%±6.2% and 70.2% ± 6.5% of normal SCBF, respectively. At 10 min and 20 min, the SCBF decreased significantly at the amplitude of MEP. At 30 min,the decrease of SCBF was not significant. The results showed that the blood supply of spinal cord decreased significantly in the first 20 min after vertebral osteotomy lead to complete spinal cord injury. After 20 min, the blood supply of spinal cord decreased gradually.Phase 5: When MEP amplitude has been down to 0 over 0.5h, restoring the line would not bring back monitoring MEP. Indicating that 0.5h after complete spinal cord injury, even if the recovery of short distance, restore normal spinal cord morphology, complete spinal cord injury could stay permanent.SCBF has been recovered, but still significantly lower than normal SCBF. There was no significant difference in SCBF between 20 min and 30 min in SCBF compared with MEP positive (MEP decreased>75%, incomplete spinal cord injury).Indicating that SCBF can restore spinal cord blood supply to incomplete spinal cord injury after a short distance to normal distance of 20 min.At the 10 min, 20 min and 30 min, the SCBF decreased to 50.2% ±9.1%, 45.1%± 7.1% and 44.5% ± 8.6%, respectively. Compared with normal SCBF, still showed a significant decline. The results showed that the SCBF recovered significantly within 20 min before the shortening of the shortening distance. After 10 min, the recovery of SCBF was not obvious and became stable.Histological observation of the spinal cordHE tissue staining observation: normal spinal cord can be seen under the normal spinal cord structure, nerve fiber arranged in rules, and no obvious bleeding, edema was caught in spinal gray matter and white matter.Otherwise ,in the sample from shortned spinal cord , obvious bleeding, edema,visible gray matter within the more exudation was caught; and visible microvascular rupture of the spinal cord,bleeding; meanwhile,gray matter can be seen within thesmall bleeding, local nerve cells appear swelling; white matter after the lateral fiber arrangement confusion, some areas can be seen spotted bleeding, and even into a film necrotic area.Electron microscopy: In normal spinal cord electron microscopy, it showed neuronal cell membrane integrity, and intracellular structure is clear, mitochondria,nuclear membrane and rough endoplasmic reticulum integrity, nuclear chromatin particles distributed evenly, no chromatin agglutination. Articular myelin arrangement, structural integrity, no stratification and disintegration; neuronal structure is normal, mitochondrial structure can be seen completely.Shortening of the spinal cord can be seen more central gray matter of necrotic neurons,blurred structure,the nucleus dissolved,organelles swelling,the emergence of nuclear membrane and cell membrane disintegration, transparent vacuoles.Myelinated lamellar structure disorder, myelin and axonal gap increased, nerve fiber edema significantly. Part of the axon within the structure disappeared, wearer axon sheath thinning, the structure is not obvious, visible demyelination.Conclusion: Vertebral osteotomy longitudinal compression shortening can cause acute spinal cord injury. It is feasible to establish a mammalian spine osteotomy spinal cord shortening model, and the experimental results are reliable.As vertebral osteotomy shortening distance less than 70% of the height of the thoracic vertebral body, less than 85% of the average height of thoracolumbar spine,it will not cause spinal cord injury. At this point,it can lead to a slight increase in spinal cord blood flow. When the shortening distance is equivalent to the osteotomy of the vertebral height of 80% and the average height of the thoracic and lumbar spine, it can lead to incomplete spinal cord injury, and spinal cord blood flow decreased significantly. When the shortening distance is equivalent to the height of the vertebral body, the average thoracolumbar height of 1.2 times, it can lead to complete spinal cord injury, spinal cord blood flow decreased more significantly.A significant correlation between the vertebral osteotomy longitudinal compression shortening and monitoring of motor evoked potentials and spinal cord blood flow were proved, indicating that tortuous spinal cord distortion, spinal cord blood flow changes caused by osteotomy could lead to spinal cord injury.