Snyder B D, Zaltz I, Hall J E, Emans J B
Department of Orthopaedic Surgery, Harvard Medical School, Children's Hospital, Boston, Massachusetts, USA.
Spine (Phila Pa 1976). 1995 Jul 15;20(14):1568-74. doi: 10.1097/00007632-199507150-00004.
Using 2-week-old calf lumbar vertebrae as a model for the human adolescent spine, the strength and rigidity of different methods of anterior spinal screw fixation and the use of noninvasive techniques for predicting bone screw stability before surgery and screw insertional torque intraoperatively were investigated.
The objectives were to determine what factors most affect the strength and rigidity of screw fixation, to determine the strongest and most rigid type of screw fixation for anterior spinal instrumentation, and to determine if noninvasive measurements of bone density before surgery by dual energy x-ray absorptiometry or quantitative computed tomography and if intraoperative measurement of screw insertional torque can be used to predict the in vivo strength and rigidity of vertebral screw fixation.
Anterior spinal instrumentation is an efficient method to correct spinal deformities in the thoracolumbar and lumbar spine. Fewer vertebrae are instrumented and arthrodesed, allowing for greater spine mobility. The forces transmitted to each vertebra are higher, perhaps accounting for the clinical failure rate of 13-30% at the metal bone interface from screw cut out.
Quantitative computed tomography and dual energy x-ray absorptiometry were used to assess the bone density of 24, 2-week-old calf lumbar vertebrae. Four different methods of vertebral screw fixation were evaluated: unicortical screw, bicortical screw, bicortical screw and washer, and bicortical screws and staple. The maximal screw insertional torque was measured for each specimen. Each vertebral body-screw construct failed in a mode simulating in vivo screw cut out. The applied moment and rotatory displacement were recorded. Ash density was measured for each vertebral body after removing all hardware.
Noninvasive measures of bone density varied linearly with ash density (P < 0.01). Screw insertional torque varied linearly with bone mineral content and bone mineral density (r2 = 0.50) and was correlated with the yield moment for all types of fixation except the staple. Density measured by quantitative computed tomography did not affect rigidity or yield moment. Post hoc analysis showed that the screw-staple construct was the strongest and most rigid form of fixation.
Measurement of bone density before surgery using dual energy x-ray absorptiometry and intraoperative measurement of screw insertional torque can be used to assess the stability of anterior spinal instrumentation. A bicortical screw inserted through a Dwyer-type staple provided the strongest and most rigid form of fixation.
以2周龄小牛腰椎作为人类青少年脊柱模型，研究不同前路脊柱螺钉固定方法的强度和刚度，以及术前使用非侵入性技术预测骨螺钉稳定性和术中螺钉插入扭矩的情况。
确定哪些因素对螺钉固定的强度和刚度影响最大，确定前路脊柱内固定最强且最具刚性的螺钉固定类型，以及确定术前通过双能X线吸收法或定量计算机断层扫描进行的骨密度非侵入性测量和术中螺钉插入扭矩测量是否可用于预测椎体螺钉固定的体内强度和刚度。
前路脊柱内固定是矫正胸腰椎和腰椎脊柱畸形的有效方法。固定和融合的椎体较少，可使脊柱具有更大的活动度。传递到每个椎体的力更高，这可能是螺钉穿出导致金属-骨界面临床失败率达13% - 30%的原因。
使用定量计算机断层扫描和双能X线吸收法评估24个2周龄小牛腰椎的骨密度。评估四种不同的椎体螺钉固定方法：单皮质螺钉、双皮质螺钉、双皮质螺钉加垫圈以及双皮质螺钉加钉板。测量每个标本的最大螺钉插入扭矩。每个椎体-螺钉结构以模拟体内螺钉穿出的模式失效。记录施加的力矩和旋转位移。去除所有硬件后测量每个椎体的灰密度。
骨密度的非侵入性测量与灰密度呈线性变化（P < 0.01）。螺钉插入扭矩与骨矿物质含量和骨矿物质密度呈线性变化（r2 = 0.50），并且与除钉板外所有固定类型的屈服力矩相关。定量计算机断层扫描测量的密度不影响刚度或屈服力矩。事后分析表明，螺钉-钉板结构是最强且最具刚性的固定形式。
术前使用双能X线吸收法测量骨密度和术中测量螺钉插入扭矩可用于评估前路脊柱内固定的稳定性。通过Dwyer型钉板插入的双皮质螺钉提供了最强且最具刚性的固定形式。
