Ryken T C, Clausen J D, Traynelis V C, Goel V K
Division of Neurosurgery, University of Iowa, Iowa City, USA.
J Neurosurg. 1995 Aug;83(2):325-9.
The bone mineral density (BMD) of 99 cadaveric cervical vertebral bodies (C3-7) was determined using dual x-ray absorptiometry. The vertebral bodies were randomly assigned to receive either a unicortical (51 bodies) or bicortical (48 bodies) Caspar cervical plating screw. The initial insertion torque was measured using a digital electronic torque wrench, and the force required to withdraw the screw from the vertebral body was determined. The mean BMD for the total group of 99 was 0.787 +/- 0.154 g/cm2, the mean insertion torque was 0.367 +/- 0.243 newton-meters, and the mean pullout force was 210.4 +/- 158.1 newtons. A significant correlation was noted between BMD and torque (p < 0.0001, r = 0.42), BMD and pullout force (p < 0.0001, r = 0.54), and torque and pullout force (p < 0.0001, r = 0.88). Although the BMD of the unicortical and biocortical groups was equivalent (p = 0.92), the insertion torque and pullout force differed significantly (p = 0.02 and p = 0.008, respectively) for the unicortical and bicortical groups. A holding index for each screw and insertion technique was defined as the product of the BMD and insertion torque. The calculated holding index and resultant pullout force were significantly correlated for both techniques of screw insertion (r = 0.92), and a significant difference in holding index was observed with unicortical versus bicortical screw placement (p = 0.04). The determination of BMD and measurement of insertion torque to create a unique holding index provides an assessment of bone-screw interaction and holding strength of the screw, both of which impact on the resultant stability of cervical instrumentation. As the number of cervical plating systems increases, the determination of a holding index for various screws and insertion techniques may assist in the comparison of cervical instrumentation.
采用双能X线吸收法测定了99个尸体颈椎椎体（C3 - 7）的骨密度。将椎体随机分为两组，分别植入单皮质（51个椎体）或双皮质（48个椎体）的Caspar颈椎钢板螺钉。使用数字电子扭矩扳手测量初始插入扭矩，并测定将螺钉从椎体中拔出所需的力。99个椎体的总平均骨密度为0.787±0.154g/cm²，平均插入扭矩为0.367±0.243牛顿米，平均拔出力为210.4±158.1牛顿。骨密度与扭矩之间存在显著相关性（p < 0.0001，r = 0.42），骨密度与拔出力之间存在显著相关性（p < 0.0001，r = 0.54），扭矩与拔出力之间也存在显著相关性（p < 0.0001，r = 0.88）。虽然单皮质组和双皮质组的骨密度相当（p = 0.92），但单皮质组和双皮质组的插入扭矩和拔出力存在显著差异（分别为p = 0.02和p = 0.008）。为每个螺钉和插入技术定义了一个固定指数，即骨密度与插入扭矩的乘积。两种螺钉插入技术的计算固定指数与最终拔出力均显著相关（r = 0.92），单皮质与双皮质螺钉置入的固定指数存在显著差异（p = 0.04）。测定骨密度和插入扭矩以创建独特的固定指数，可评估骨 - 螺钉相互作用以及螺钉的固定强度，这两者都会影响颈椎器械植入后的最终稳定性。随着颈椎钢板系统数量的增加，确定各种螺钉和插入技术的固定指数可能有助于比较颈椎器械。
