Predicting the Integrity of Vertebral Bone Screw Fixation in Anterior Spinal Instrumentation
Predicting the Integrity of Vertebral Bone Screw Fixation in Anterior Spinal Instrumentation
复制标题
预测前路脊柱器械中椎骨螺钉固定的完整性
作者：
B. Snyder;I. Zaltz;J. E. Hall;J. Emans
Study Design Using 2-week-old calf lumbar vertebrae as a model for the human adolescent spine, the strength and rigidity of different methods of anterior apinal screw fixation and the use of noninvasive techniques for prediting bone screw stability before surgery and screw insertional torque intracperatively were investigated. Objectives 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 nonivasive measurements of bone density before surgery by dual energy x-ray abosrptiometry or quantitative computed tomography and if intraoperative measurement of screw insertional forque can be used to predict the in vivo strength and rigidity of vertebral screw fixation. Summary of Background Data Anterior spinal instrumentation is an efficient method to correct spinal deformities in the thoracolumbar and lumbar spine. Fewer vartebrae 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. Methods 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. Results Noninvasive measures of bone density varied linearly with ash density; (P < 0.01). Scerew insertional torque varied linearly with bone mineral content and bone mineral density (r2 = 0.50) and was corelate 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 figid form of fixation. Conclusions 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 figid form of fixation.
