The Effection Of Different Month Age Rabbit With Different Range Posterior Spinal Hemifusion And Fixation On Spinal Growth

Objective: The purpose of this study is to explore the effection of different month age rabbit with different range spinal hemifusion and fixation on spinal growth, and offer theoretical bases to the selection of spinal fusion range in treatment of scoliosis. Scoliosis is the common disease in spinal deformity in Children and teenagers, and the treatmental method correlates closely to the law of spinal growth. The clinical important topic and problem is grasp the best way 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 hemifusion 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 hemifused and fixated with steel wire by posterior technique in subgroup a1 and b1 , five segments in subgroup a2 and b2 ,seven segments in group a3 and b3 .The allograft bones from allogeneic rabbits were grafted to the left side of 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,anterior,right and left border length of vertebral body. When biting spinous process and lumina of vertebral, the fusion block was harvested, with dimension of 1*0.5 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,right and left border 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 paralysis, producing different degree lordosis and scoliosis. Lordosis and scoliosis are 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 and anterior,right and left border 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 and right portion of vertebral endplate became thicker with more active cellproliferation than posterior and left portion. The posterior and left portion of the disc spaces and intervertebral disc in these rabbits were narrower than the anterior and right 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 and scoliosis at 6 months old, and significant difference (p<0.01) in angle between 2 weeks after surgery and 6 months old. The ANOVA for sagittal and frontal Cobb angle of each subgroup in double group which having same age and different fusion range, showed overall difference(p<0.05). The SNK-q test for sagittal and frontal Cobb angle of each subgroup showed substantial statistic significance(p<0.05). 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 and frontal Cobb angle in subgroups with same age and different fusion range showed significant difference (p<0.05). The multiple linear regression for age, fusion range and sagittal,frontal Cobb angle obtained the multiple linear regression formula: ?1= 1.6701﹣0.9376 x1+1.0338 x2;?2= 4.5494﹣2.0469 x1+2.2928 x2. There was a positive correlation with fusion range and sagittal,frontal Cobb angle, and negative correlation with age and sagittal,frontal Cobb angle. 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 hemifusion and fixation operated on quadruped, the resulting deformity is different of clinical, however, the fundamental mechanism is same. So, the the quadruped 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 hemifusion in the skeletal immature patient, because of the potential of 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 and the time of arthrodesis should as late as possible on the important premise of therapeutic efficacy in clinical. (5) To avoid the inevitability of the crankshaft phenomenon, recommendiations were made that a combined anterior and posterior fusion be done in skeletal immature patient. (6)For young patients with scoliosis who have large potential of growth ,operation of expand on concave side or tether on convex side can be used to decrease the effect of early arthrodesis on spine and thorax.