The Effection On Spinal Growth And Development Of Different Month Age Rabbit With Different Range Posterior Spinal Fusion And Fixation In Experimental Study

Objective: The purpose of this study is to explore the effection on spinal growth and development of different month age rabbit with different range spinal fusion and fixation, and offer theoretical bases to the selection of spinal fusion range in treatment of scoliosis. Scoliosis is the common disease in spinal deformity of Children and teenagers, and the treatmental result correlate closely to the law of spinal growth. The clinical important topic and problem is grasp the best occasion of treatment, and tackle reasonably contradiction between spinal fusion and spinal growth. Because of growth potential in Children and teenagers'spine, sometimes although obtaining a good treatmental result and fusion, deformities become more severity after operation step by step, this is called Crankshaft Phenomenon. In this study, animal model similar to the patient after operation of scoliosis be made, posterior fusion of different range is proceed in different month age rabbits, with the purpose of observing the changes in rabbit's spine. The main observations include: gross appearance, light microscope(HE sections), radiological outcomes. Through these observations, the mechanism of crankshaft phenomenon and the relation between skeleton maturity or/and fusion range and crankshaft phenomenon can be explained, and the instruction to selection of operative occasion and fusion range in clinical can be analysed. Methods: 48 rabbits were divided into 2 groups, 24 each namely group A and group B. The rabbits in group A was 6 weeks old and 15 weeks old in group B. Each group was randomly divided into 3 subgroups, namely a₁, a₂, a₃ and b₁, b₂, b₃ .Three lumbar segments were fused and fixated with steel wire by posterior technique in subgroup a₁ and b-1 , five segments in subgroup a₂ and b₂ ,seven segments in group a₃ and b₃ .The allograft bones from allogeneic rabbits were grafted to the spinous process, lamina of vertebra and transverse process. The allograft bones were produced from iliac and scapula of 8 killed white rabbits under sterile technique, and were frozen at -86°C. For each rabbit, biplanar radiographs (posterioranterior and lateral) of the spine were done at 2 weeks after surgery and 6 months old, and the Cobb angle in the frontal and sagittal planes were measured. Observations were processed by statistics. At the time of sacrifice, the lumbar spine was carefully excised, then gross appearance was observed. The rabbits of nonunion were excluded before measuring the posterior and anterior length of vertebral body. When biting spinous process and lumina of vertebral, the fusion block was harvested, with dimension of 1*1 cm. The tissue blocks were fixed in 10%neutral buffered formalin for 72 hours. Another intact tissue blocks from each group were harvested included inferior endplate of L4 , superior endplate of L₅ and interverbral disc between both endplate, and were fixed in 10% neutral buffered formalin for 48 hours, and for histological hematoxylin. The observations gratified request were analysed by statistics , main include: (1) Difference of posterior and anterior length of vertebral body: Analysis of variance (ANOVA) and SNK-q test were used to specimens with different fusion range in same group, and t-test to specimens with same fusion range in double group, inorder to analyse whether having difference in statistics. (2) Cobb angle in the frontal and sagittal planes: The statistics method indentical to (1), were used to observe the changes of Cobb angle from 2 weeks after surgery to 6 months old. (3) Correlation between age, fusion range and Cobb angle in the sagittal plane: Multiple linear regression was used to analyse the correlation between age, fusion range and Cobb angle in the sagettal plane, and relative coutribution from age, fusion range to Cobb angle. Results: (1) Gross appearance: Posterior tethering and anterior column growth occurred in each group excluding nonunion and death because of infection and paralysis, producing different degree lordosis. There are no transparent scoliosis. Lordosis is most obvious in a₃ subgroup. Wedging of vertebral body produced in fusion spine, and most obvious in apex vertebrae. The ANOVA for difference of posterior andanterior length of vertebral body showed significant difference(p<0.01) after surgery in subgroup with same fusion range. There were overall difference between each subgroup in same group(p<0.05), the most difference in a3 and b3 , the less in a1 and b1 . The difference is more obvious in group A than group B. (2) Light microscope (HE): The anterior portion of vertebral endplate became thicker with more active cellproliferation than posterior portion. The posterior portion of the disc spaces and intervertebral disc in these rabbits were narrower than the anterior portion, with the intervertebral disc wedging. Bone-healing of allograft showed in section of tissue blocks, and entranced into bone-formation phase or moulding phase, and produced mass fibrous bone and lamellar bone. (3) Radiological outcomes: There were no significant difference in the frontal and sagittal Cobb angle(p<0.05) at 2 weeks after surgery. But there were substantial lordosis at 6 months old, no obvious scoliosis and spinal rotation, and no significant difference (p>0.5) in frontal Cobb angle between 2 weeks after surgery and 6 months old. The ANOVA for sagittal Cobb angle of each subgroup in double group which having same age and different fusion range, showed overall difference(p<0.01). The SNK-q test for sagittal Cobb angle of each subgroup showed substantial statistic significance(p<0.01). The difference in absolute value of q was maximum at two subgroup which fusion range was three and seven segments. The t-test for sagittal Cobb angle in subgroups with same age and different fusion rangeshowed significant difference (p<0.01). The multiple linear regression for age, fusion range and sagittal Cobb angle obtained the multiple linear regression formula: ?= 6.7915ï¹£0.5289 x1+2.4869 x2 . There was a positive correlation with fusion range and sagittal Cobb angle, and negative correlation with age and sagittal Cobb angle. The absolute value of standardized partial regression coefficient of the fusion range variable was greater than of age variable, namely the relative contribution of the former greater than the latter. The F-test for regression formula showed obvious statistic significance between age, fusion range and sagittal Cobb angle. Conclusion: (1) In this study, posterior spinal fusion and fixation operated on reptile, the resulting deformity is different of clinical, however, the fundamental mechanism is same. So, the the reptile can be used to model scoliosis. (2) Allograft that produced by profound hypothermia can be used to spinal fusion, the rate of nonunion is low, and obtain a better bone-healing. (3) Posterior spinal fusion in the skeletal immature patient, because of the potential of anterior spinal column growth, the deformity would be more severity step by step. The more the skeletal immaturity and fusion range, the more the spinal deformity after posterior spinal fusion and fixation. It same as the clinical result. (4) The skeletal maturity and fusion range correlate obvious to the spinal deformity after surgery, the relative contribution of fusion range is greater than skeletal maturity. So the fusion range should be decreased as far as possible on the important...