| [Background]Scoliosis is a kind of spinal deformity with a Cobb angle of more than 10° in the coronal plain. It can be divided into three groups such as congenital scoliosis, idiopathic scoliosis and degenerative scoliosis according to the pathogenesis. Idiopathic scoliosis (IS) is the most common one which can occur in the thoracic vertebra, thoracolumbar and lumbar with the morbidity of 1%-3%. Adolescent idiopathic scoliosis accounts for 80% of the idiopathic scoliosis. IS mainly performs one or several curves to the lateral of several vertebras in the coronal plains with kyphosis and/or rotation. Patients with progressing scoliosis would be less mental health due to the disturbed self-image caused by IS. If there was still no effective therapy, Thoracic Insufficiency Syndrome would occur which led to pulmonary and cardiac complaints in life, even worse death. So it’s significant to study the pathogenesis of IS and develop ways to prevent and cure the disease.The pathogenesis of IS is still not clear so far. Studies demonstrate that asymmetric load plays an important role in idiopathic scoliosis. Hueter-Volkmann law shows that increasing of the load will inhibit the bone growing and the bone growing is promoted on the contrary. In patients with scoliosis, the load focuses on the concave side of the spine, especially the apex so that the concave side of the vertebra grows more slowly. The end-plate is a kind of structure which formed by the superior and inferior surface of vertebra after the osteoepiphysis stops ossifying. It, which can be divided into cartilage end-plate and bone end-plate, originates from the secondary ossification center of vertebra and is important to the growth of the vertebra. Besides, there is no vascular in the intervertebral disc since the 4th year after being born and the vascular in the end-plate supplies the most nutrients for the intervertebral disc. So any factors which will affect the end-plate will affect the intervertebral disc. When the asymmetric force is loaded on the end-plate, the structure of it will change and so is the nutrients supplement of intervertebral disc which aggravate the asymmetric changes of it. Although a lot of work relevantly is demonstrated, further studies are still needed and a proper scoliosis model is necessary.A good scoliosis model is important to develop the pathogenesis of scoliosis and new therapies to it. As some literature shown, Von Lesser is the first one who reported a scoliosis model which was built in rabbits by unilateral phrenic resection. From then on, knowledge about scoliosis has been promoted due to plenty of scoliosis models were built. The model building ways can be divided into 3 types such as local procedures, systemic intervention and immobilization and tethering. Unilateral phrenic resection, the way Von Lesser used, is belonged to local procedures. Pinealectomy on chicken, belonging to systemic intervention, was put forward by Thrillard in 1959. They performed the pinealectomy on chicken resulting in a thoracolumbar scoliosis. Based on that, Machida et al. pursued this theory and found that melatonin and serotonin played an important role in this procedure. This led to the hypothesis that neurohormonal system in the pineal body was the major contributing factor in this type of experimental scoliosis. Although pinealectomy on chicken is a classical experimental scoliosis, it could not work well on mammalian. Besides those, immobilization and tethering is also a common way, especially the asymmetric tethering model due to its convenience and reproducibility which lead to be one of the most commonly used way. In the past, the researchers used rigid tethering which depended on the potential of growth. When the animal was mature, the way would not be so effective. So the elastic tethering appeared which could be more stable and effective than rigid tethering. Braun succeeded in experimental scoliosis on female sheep by elastic tethering on left T5 to L1 used artificial ligament and proved it could regulate the spinal growth. So did Schwab who performed on 11-week pigs. But the pedicle screws used in this way would make destruction on facet joints and affect the stabilization of spine. An improved way is still needed.In our study, we created a new experimental scoliosis model by applying asymmetric load on unilateral transverse process using 316L stainless spring. And we observed the Cobb angle by X-ray examination. A further investigation on the change of Cobb angle after asymmetric load removing was performed to prove the sustainable asymmetric load is important to the progress of scoliosis in the type of experimental scoliosis. We also tried to explain the effect that the asymmetric load worked on vertebra by observing the BV/TV of end-plate using MicroCT.[Objective]1. To develop a new experimental scoliosis model in rabbits by asymmetric load using 316L stainless spring.2. To explain the effect that the asymmetric load worked on vertebra by observing the BV/TV of end-plate using MicroCT.[Methods]1. Scoliosis was induced in 10 two-month-old New Zealand rabbits using 316L stainless steel springs. Operations were performed to put the springs between the unilateral transverse processes of L2 and L5 in all 10 rabbits. Serial radiographs were documented before the operation, so were in the 1st,4th,8th,9th and 12th week after that. After the radiographs were recorded in the 8th week, all the rabbits were randomly divided into 2 groups:in group SR(n=5), the spring was removed after 8 weeks and in group SK(n=5), the spring would be kept till the end.2. After 12th week, all rabbits were sacrificed by air embolism. The apex, the upper vertebra and the lower vertebra were obtained completely to have a MicroCT scan. After that, we could get the BV/TV of the superior end-plate and the inferior end-plate in concave side and convex side separately.3. Statistical analysis was performed using SPSS13.0 statistical software. Measurement data using X±D. Comparison between two groups, if they were measurement data, unpaired t test would be used. While the BV/TV in different side were compared, paired t test would be used. If they were enumeration data or ranked data, we would apply Mann-Whitney. Comparison between the groups and multiple comparisons were conducted using variance analysis and LSD respectively. The criterion for statistical significance was P<0.05.[Results]1. Till the end of the experiment, all rabbits survived with greater Cobb angle than 10°. There was significant difference between the Cobb angles documented before operation and that in 1 week post-operation,4 weeks post-operation and 8 weeks post-operation (p<0.05), so is the kyphosis. At the eighth week, the Cobb angle, the kyphosis and the length of the spring between Group SR and Group SK were no difference(p>0.05).Then removed the springs in Group SR, the Cobb angle and the kyphosis decreased significantly than that in Group SK in the next 4 weeks(p <0.05). From the 9th week to the end of the study, the Cobb angle and the kyphosis in Group SR decreased.2. According to the Micro-CT, the BV/TV of concave side was greater than that of convex side (0.76±0.09 vs 0.73±0.10, using paired t test, t=2.627, p=0.017).3. During the procedure, the change of the length of the spring was no difference(p> 0.05).[Conclusion]1. A novel experimental scoliosis model induced by asymmetric load using 316L stainless spring is established which scoliosis can be formed in a short time respectively. Also it can demonstrate that sustainable asymmetric load plays an important role in this procedure and the asymmetric force can modulate spinal growth and result in scoliosis.2. The asymmetric load causes concave side of the vertebral end-plates tends to form a thin and dense bony plate which may adversely affect the growth of concave side of the vertebra and the nutrition supplement for the intervertebral disc. |
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