| Objective:To set up a kind of animal model of lumbar corpectomy spinal fusion, observe bone fusion conditions upon implantation of titanium cages of different diameter on vertebra resection, analyze relevant factors that impact graft of bones in spinal supporting, probe into the minimum area ratio of titanium cage section to vertebral section without impact to bone healing and biomechanical property, to guide selection of appropriate diameter titanium cage to be implanted in clinical lumbar corpectomy fusion operation.Since spinal fusion operation technology was firstly reported by Hibbs in 1911, along with development of both internal fixation technology and internal fixation materials, spinal fusion has been widely applied in treatment of spinal diseases. In the wake of social population aging and increase of incidence of tuberculosis and traffic accident, spinal tumor, spinal tuberculosis and spinal bursting fracture follow the trend; therefore vertebra resection internal fixation keeps abreast. Prior to any new bone-replacement material, internal fixation and new technology etc. are introduced to human being, at first a corresponding animal spinal fusion model need to be set up to test and study all kinds of indices, and further clinical experiment is allowed after safety of the indices are confirmed.At present there are a great variety of animal spinal fusion models with different patterns, among which small animal models are more applies than that of large animal models, and fusion effect and operation complication are different. It is reported that death rate and complication rate of New Zealand white rabbit as spinal fusion model is as much as 20%, while using large animal as spinal fusion model is more complicated. It is rather difficult to set up large animal fusion models, at present, goat is often used as spinal fusion model but is limited on cervical fusion while lumbar fusion is seldom reported as the difficult points are complicated and long time of operation, long anesthetic time, massive bleeding and more after-treatment complications. There are three patterns of animal spinal vertebra fusion model operation, namely anterior, posterior 360°and posterolateral approach. Anterior and posterior 360°model wound animals more largely, while posterolateral approach reaches vertebra via exterior of peritoneum that wounds animals relatively smaller as well as vertebra resection can be conducted by direct viewing. Therefore we probe into an effective large animal lumbar corpectomy titanium cage implantation fusion model with sound repetitiveness. For a long time, titanium cage is often used for treatment of bone defect; reasonable tailor and formation is made to titanium cage then bone block is filled, and it is implanted to targeted area to provide supporting. The technology apparently improves fusion rate of spinal implantation.However there is not a uniform specification on diameter of titanium cage implanted in clinical vertebral resection, which caused a number of problems, for instance, low healing rate after implantation, insufficient strength, bone re-fracture after removing of interior fixation, or misjudgment on healing condition and removing interior fixation before completely healed. Blindly choosing thick titanium cages makes filled bone mass increase for either autogenous or allograft bone, which causes increase of complications in bone supply area as well as economic waste to patients. Vise versa blindly choosing thin cages may lead to low bone healing rate or insufficient strength, and the cages are easily sank, which fails to strength the interior fixation and causes operation failure. By virtue of observation of implanted bone fusion condition of animal model cage of lumbar corpectomy spinal fusion, this experiment analyzes relevant factors that impact growth of bones in spinal supporting, probes into the minimum area ratio of titanium cage section to vertebral section without impact bone healing and biomechanical property and analyzes measures that can evaluate bone fusion conditions in titanium cages effectively.Methods:We set up a lumbar corpectomy spinal fusion animal model by means of titanium cage implantation plate interior fixation of posterolateral approach vertebral resection via posterolateral peritoneum. Choose nine mature goats no matter male or female at 1.5-3 years of age and 35±2.5 kg of weight; Individuality of each goat is similar to guarantee size of lumbar of goats are basically equal; the goats are divided into three groups at random with three goats in each group. All goats in three groups are single vertebral cut off and implanted diameter 10mm,12mm and 16mm titanium cages respectively; 10mm is group A,12mm is group B and 16mm is group C. The goats are feed four months after the operation and examined by X-ray on a monthly basis to observe location of the titanium cage and fusion condition. After the goats are slaughtered, their spinal samples are taken to examine by X-ray and three-dimension CT, measure CT values of contact area of titanium cage and the spine as well as CT values in different locations of the titanium cage, observe bone healing status and calculate area ratio of titanium cage section to vertebral section based on result of three-dimension CT to determine the minimum area ratio of titanium cage section to vertebral section, which is looked for in this experiment. The spine samples are taken biomechanical examination under conditions of flexion, extension, lateral and torsion to evaluate bone healing strength. In the meantime, finite element model is set up to further verify in vitro biomechanical result and analyze impact of titanium cage and lamina terminalis stress distribution to fusion of different diameter cages implantation. Samples are taken histological slice to observe contact area and implanted bone fusion status in titanium cage. Draw venous blood of the goats respectively before the operation and at the third, fifth, seventh day, two weeks and one month after the operation to separate serum, then use enzyme linked immuno assay kit to determine bone formation adjustment cytokine and metabolism markers (BMP-2,TGF-β,VEGF,BGP,BALP) serum value, observe secretion and metabolism conditions of the indices upon vertebral resection and implantation of titanium cages with different diameter, whether occurrence of peak value time and quantity of peak value are related with bone healing, as well as to observe relationship of the indices. Statistic analyses are made to all examination results.Results:Successfully set up goat lumbar corpectomy spinal fusion animal model, all goats in experiment groups survive the operation, one goat is incision infected and heals after dressing on incision; one goat's both posterior limbs paralyze incompletely but thoroughly resume after three days. Examined by postoperative three-dimension CT and measured area ratio of titanium cage section to vertebral section and CT value of contact area of titanium cage and vertebra, the result shows that area ratio of titanium cage section to vertebral section of 10mm group is 1/3, area ratio of titanium cage section to vertebral section of 12mm group is 1/2 and area ratio of titanium cage section to vertebral section of 16mm group is 2/3. Result of ratio between CT value of contact area of titanium cage and vertebra and CT value of adjacent normal vertebra shows that there are no apparent statistic differences between group B and C, but there are statistic differences between group A and B, and group A and C. There are no apparent statistic differences on biomechanical examination between group B and C, but there are statistic differences on biomechanical examination between group A and B, and group A and C. Histological slice observation shows contact area and bone trabeculae of group B and group C are compact and thick than that of group A, among which graft of group B is the best; all three groups show that the further to the contact area, the bone trabeculae is thinner and without sclerotin area. Serology bone formation adjustment and metabolism indices (BMP-2,TGF-β,VEGF,BGP,BALP) of three groups all start to increase three days after the operation and reach peak value within five days to two weeks then decrease. There are no statistics differences on peak value occurrence time, but peak value of group A is lower than that of group B and group C, and occurrence time of peak value of TGF-β,BG and BALP of group A is earlier than that of group B and C.Conclusion:The experiment successfully set up animal model of goat lumbar corpectomy spinal fusion with easy operation and sound repetitiveness, which is a relatively better way to set up spinal fusion animal model. At the time of lumbar corpectomy and titanium cage implantation, area ratio of titanium cage to vertebral section should reach 1/2 that are without apparent impact to bone healing time and strength. Occurrence time and scale of peak value of bone formation adjustment and metabolism markers have certain correlation with bone healing strength. Three-dimensional CT examination can be the first choice to evaluate bone fusion condition. |
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