可注射硫酸钙强化椎弓根螺钉内固定的实验研究

Augmentation of pedicle screw fixation strength using an injectable calcium sulfate cement:an in vivo study

目的：评估可注射硫酸钙用于强化椎弓根螺钉内固定的有效性及可行性。方法：将15只110±5kg的成年雌性猪随机分为即刻组、6周组、12周组,三组均行L1～L5双侧椎弓根螺钉置入术,L1左侧与L5右侧直接拧入螺钉作为空白对照,L1右侧与L5左侧用聚甲基丙烯酸甲酯（PMMA）强化作为PMMA对照,L2～L4双侧椎弓根螺钉均用可注射硫酸钙强化。至指定时间点处死动物取材,所有腰椎均行正侧位X线拍片及骨密度检查。每只实验动物的L2、L4、L5用于最大拔出力实验;L1及L3经塑料包埋及切片后在扫描电镜下观察并测量螺钉周围骨组织层的厚度。统计学方法使用OnewayANOVA。结果：正侧位X线片显示椎弓根螺钉位置理想,定位准确。大体观察无感染,无异常骨反应。各组椎体的骨密度经方差分析无显著性差异。即刻空白组最大拔出力为1.03±0.16kN,硫酸钙组为1.92±0.27kN,PMMA组为3.63±0.55kN;6周时空白组为1.26±0.09kN,硫酸钙组为1.85±0.28kN,PMMA组为3.75±0.56kN;12周时空白组为1.32±0.10kN,硫酸钙组为2.04±0.34kN,PMMA组为3.72±0.61kN,各时间点三组间的差异均有统计学意义（P〈0.001）。扫描电镜下测量螺钉周围骨组织层的厚度,即刻空白组为231±33μm,硫酸钙组为244±28μm,PMMA组为255±25μm,三组无显著性差异（P〉0.54）;6周时空白组为256±24μm,PMMA组为267±37μm,两组比较无显著性差异（P〉0.69）,硫酸钙组边界不清,无法测量;12周时空白组为244±44μm,PMMA组为253±29μm,两组差异无统计学意义（P〉0.59）,12周硫酸钙组为972±62μm,显著大于空白组及PMMA组（P〈0.002,P〈0.001）,也显著大于即刻硫酸钙组（P〈0.001）,硫酸钙完全被吸收。结论：可注射硫酸钙可有效强化椎弓根螺钉内固定的强度,其强化作用不随时间推移而降低,且在12周内可完全被自体骨替代。

Objective：To investigate the long-term in vivo biomechanical performance of pedicle screws augmented with calcium sulfate cement.nethod：10 pedicle screws were implanted into the lumbar vertebrae of 15 adult female landraces weighing 105-115kg.The pedicle srcrews in the left pedicles of the L1 vertebrae and the eight pedicles of the L5 vertebrae were not augmented as control groups,the pedicle srcrews in the right pedielcs of the L1 vertebrae and the left pedicles of the L5 vertebrae were augmented with polymethyl methacrylate （PMMA） as PMMA groups,the pedicle srcrews in the pedicles of the L2,L3 and IA vertebrae were augmented with the calcium sulfate cement as calcium sulfate groups.The landraces were randomly divided into 3 groups based on study periods including immediate（n=5）,6 weeks（n=5） arid 12 weeks（n=5）.At the end of each assigned study period ,the animals were sacrificed and axial pull out tests and histological analyses were conducted on the isolated specimen vertebrae.The bone mineral density of the vertebral bodies were measured using dual-energy X-ray absorptiometry before the biomechanieal tests.The Oneway ANOYA was used to evaluate the difference in the bone mineral density,pull-out strength and the thickness of the bone walls around the screws.Result：Mean bone mineral densityof all groups was similar.The maximum pull out strength （POS） of the immediate control group,calcium sulfate group and PMMA group was 1.03±0.16kN, 1.92±0.27kN and 3.63±0.55kN respectively.The maximum POS of the 6-week control group,calcium sulfate group and PMMA group was 1.26±0.09kN,1.85±0.28kN and 3.75±0.56kN.The maximum POS of the 12-week control group,calcium sulfate group and PMMA group was 1.32±0.10kN,2.04±0.34kN and 3.72±0.61kN.Among which significant differences were found at each time point （P〈0.001）.Histologically,the thickness of the bone tissue in the immediate control group,calcimn sulfate group and PMMA group was 231±33μm,244±28μm and 255±25μm respectively,among which no significant difference was found （P〉0.54）.The thickness of the bone tissue in the 6-week control group and PMMA group was 256±24μm and 267±37μm respectively, no significant difference was found between them （P〉0.69）.The thickness of the bone tissue in the 12-week control group,calcium sulfate group and PMMA group was 244±44μm,972±62μm and 253±29μm respectively,no significant difference found between control and PMMA groups, however the bone tissue in the 12-week calcium sulfate group was significantly thicker than that of the other two groups （P〈0.002,P〈0.001）,and also significantly thicker than that of the immediate calcium sulfate group（P〈0.001 ）.Conclusion：The injectable calcium sulfate cement can significantly improve the immediate pull out strength of pedicle screw fixation,and this effect can be maintained even if the calcium sulfate cement has been absorbed completely as it can be substituted by autogenous bone ingrowth,Calcium sulfate cement may be a good alternative to PMMA for the augmentation of pedicle screw fixation.