钕铁硼磁体模拟脊柱后路不对称栓系对小型猪脊柱生长的影响——小型猪脊柱侧凸模型的构建

Effect of Mimic Posterior Asymmetric Tether by Magnetic Force on Spinal Growth of Immature Mini-pig(Establishment of an Experimental Scoliosis Model)

目的构建脊柱侧凸动物模型,探讨特发性脊柱侧凸病因学和发病机制,验证脊柱生长失衡假说。方法利用钕铁硼磁体的相互吸引力模拟后路经椎弓根不对称栓系相邻椎体,观察后路栓系对小型猪脊柱生长的形态学三维影响,提出导致脊柱发生畸形的可能阈值范围。16只1月龄雌性小型猪〔体质量为(7.54±0.46)kg〕分为对照组和实验组,每组8只。实验组于T8、T9、T10胸椎后路左侧经椎弓根植入直径为25 mm螺钉和磁体,保持相邻磁体间极性相吸和维持5 mm内距离。对照组仅植入螺钉。每隔4周复查脊柱正侧位片,直至12周。测量体质量、冠状位Cobb角、胸椎后凸角、顶椎(T9)两侧高度及椎体间磁力值的范围,采用完全随机设计量总体均数比较的t检验,确定2组的统计学差异。结果12周后小型猪平均体质量增加约2倍,实验组:(21.05±1.67)kg,对照组:(21.75±1.67)kg,P=0.769,2组差异无统计学意义。对照组小型猪1月龄时T9椎体高度为(6.5±0.60)mm,12周后为(13.06±1.37)mm,平均增加约1倍。实验组小型猪T8-T10的脊柱冠状位Cobb角为11.75°±2.87°,对照组为0.94°±0.86°,差异有统计学意义(P<0.000 1)。实验组矢状面出现胸椎前凸畸形,平均为-5.25°±6.21°,对照组为脊柱后凸,平均为4.25°±0.71°,差异有统计学意义(P=0.003)。结论钕铁硼磁体后路经椎弓根单侧不对称栓系小型猪T8-T10椎体,可以影响其脊柱的生长发育,并可以诱导出猪脊柱冠状面轻度的侧凸畸形和矢状面的前凸畸形。钕铁硼磁体对小型猪椎体生长板产生的栓系力约为1.0～2.3 N。本实验结果验证脊柱侧凸发病机制的脊柱生长失衡假说并且遵循Hueter-Volkmann法则,脊柱后路不对称栓系在脊柱侧凸畸形发生及进展中起重要作用,矢状面的前凸可能是脊柱侧凸的原发畸形。

Objective To explore the etiology and pathogenesis of idiopathic scoliosis by creating experimental scoliosis as well as validate the hypothesis of spinal growth imbalance. To determine the magnitude ranges of spinal tether force and observe the changes of mini-pig＇s spinal deformity in three-dimensional sections by posterior transpedicle screws with Nd-Fe-B magnetic materials. Methods Sixteen mini-pigs （female, 4 weeks old, （7.54 ± 0.46）kg were randomly arranged averagely into tethering group and control group. Leftside posterior transpedicle screws （25 mm） with magnets were placed into vertebrae from T8 to T10 in tethering groups and maintained the proper magnetic polarity within distance of 5 ram; in the control group pigs underwent operation only using pedicle screws; they were all checked by A-P and lateral X-ray films every 4 weeks until 12 weeks to measure items responded to degrees of spinal deformity including weights and Cobb angles in coronal section and sagittal kyphosis and the heights of apex vertebral （T9 ） between two sides as well as magnitudes of magnetic forces among the involved vertebrae. Results Mean weights of mini-pig increased about 2 times in 12 weeks （21.05 ± 1.67 ） kg in tethering group and （21.75kg ± 1.67） kg in control group, P 〉 0.05）. The heights of T9 vertebral increased double during 12 weeks from 6.5 mm ±0.6 mm to 13.06 mm ± 1.37 mm in control group. The radiographic analysis demonstrated scoliosis of 11.75° ± 2.87° in T8-T10 tethered segments, as compared with 0.94° ± 0.86° in the control group （P 〈 0. 001 ）. Similarly, thoracic lordosis developed in the tethered segments -5.25° ± 6.21°, as eompared to 4.25° ± 0.71° at the control levels （P = 0. 003）. Conclusion The asymmetrical tethering performed by transpedicle screws with Nd-Fe-B magnets upon the vertebral body T8-T10 of minipigs can modulate their spinal growth and create the mild scoliosis in coronal section and lordosis in sagittal section, the magnitude range of magnetic force upon spinal growth plates is from 1.0 N to 2.3 N. This method validate the hypothesis of spinal growth imbalance related scoliosis pathology and abide by the Hueter-Volkmann law. The asymmetrical posterior tethering of spine have an important role in scoliotie onset and progressing, lordosis in the sagittal section may be the primary deformity of seoliosis.