胸椎经椎弓根内固定器的研制与生物力学的测试

为设计一种胸椎经椎弓根内固定器 ,同时与Dick钉进行生物力学对比研究 ,用游标卡尺对 10具成人胸1～ 11椎体干燥标本、2 0份MRI和CT片的椎弓根高度、宽度、长度、进钉点及椎弓根轴线的角度、椎弓根之间的宽度、椎弓根的毗邻等进行观测 ,并将 10具新鲜成人尸胸2 ～胸11椎体标本制成屈曲压缩骨折模型和屈曲牵张型损伤模型 ,用Dick钉和ARRIF Ⅱ型分别固定在胸7和胸10 及胸4 和胸6的椎弓根内 ,进行三维方向上的生物力学测试。结果确定进钉点在上位椎体下关节突下缘的外缘线上 3mm处 ,与矢状线的夹角在 15°～ 2 0°。胸4 以上椎体可容纳直径 4 0mm、长度 3 0～ 3 5cm的椎弓根螺钉 ,胸4 以下椎体可容纳直径 5 0mm、长度 3 5～ 4 0cm的椎弓根螺钉。ARRIF Ⅱ型在三维方向上具有较好的应力遮挡 ,抗扭转力矩较Dick钉大 ,ARRIF Ⅱ型椎弓根螺钉均在椎弓根内。说明胸椎经椎弓根螺钉可较安全地置入椎弓根 ,内固定器能很好地复位骨折椎体 ,间接减压椎管。

THE MAKING OF THE THORACIC SPINE TRANSPEDICULAR INTERNAL FIXATORS AND THE COMPARATIVE STUDY OF BIOMECHANICS

To design a kind of thoracic transpedicular internal fixator and make comparative study between it and Dicks′. The three dimensional quantitative anatomy of thoracic spine pedicles was determined in 10 adult dry thoracic spine specimens,and 20 MRI and CT pictures using vernier caliber,including the height,the width,the length,the axis angulation of the pedicle,the point of the screw penetration,the width between two pedicles,the adjacent structure,etc.Flexion compression fracture and flexion expansion fracture were produced in 10 fresh adult spine including T2 to T11 vertebrae.Dicks′ plate was used to fix T7 to T10,and ARRIF-Ⅱ for T4 to T6.Biomechanics was then studied in three dimension.The entrance point of the screw was located in the external edge of inferior articular trabecala of the upper vertebrae and 3 mm below lower edge of inferior articular trabecala,and the angle of the screw was 15～20 degrees in sagittal plane.The vertebrae up to T4 can accept pedicular screws of 4.0 mm in diameter and 3.0～3.5 mm in length,and that below T4 can accept screws of 5.0 mm in diameter and 3.5～4.0 mm in length.The ARRIF-Ⅱ type fixators have better stress-shielding in three dimensions.They also have stronger anti-torsion property than the Dicks′.All the screws of ARRIF-Ⅱ type remained in pedicles. The transpedicular screw of thoracic vertebrae can be placed safely into pedicle,and the internal fixators may reduce vertebral fracture and decompress vertebral canal indirectly.