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目的 研究骶骨螺钉固定在承受周期性载荷后的拔出强度,评价前内、前外侧和单、双边皮质螺钉固定的生物力学作用.方法 对11 具新鲜成人尸体的骶骨行定量CT(QCT)扫描以确定S1 椎体和骶骨翼的骨矿物质密度.CCD骶骨螺钉分别放置在骶骨的前内、前外侧和单、双边皮质等四个位置上,测量螺钉固定时旋入的力矩.对螺钉施加40~400 N 的垂直周期性载荷,载荷频率为2Hz,加载次数为20 000 次.然后行螺钉拔出试验,获得螺钉最大拔出力.结果 S1 椎体和骶骨翼的平均骨矿物质密度分别为0-38 g/ml 和0-24g/ml.双边皮质螺钉固定时的旋入力矩和最大拔出力均显著大于单边皮质螺钉.而无论是单边或双边皮质固定, 内侧螺钉固定的旋入力矩和最大拔出力都显著高于外侧螺钉.内侧螺钉固定的最大拔出力与S1 椎体的骨矿物质密度和旋入力矩呈线性相关.结论对于年轻人群, 骶骨螺钉固定的方向对螺钉固定的最大拔出力的影响比螺钉插入深度的影响要大,前内侧螺钉固定要明显强于前外侧螺钉固定.S1 椎体骨矿物质密度和螺钉旋入力矩可分别反映螺钉在术前和术中的固定强度“,”Objective To evaluate the effects of fatigue loading on the pull out strength of medial and lateral unicortical and bicortical sacral screws Methods Eleven fresh specimens of human sacrum were used in this study Bone mineral density (BMD) at the vertebral body and the ala were determined by peripheral quantitative computed tomography Seven millimeter compact CD sacral screws were inserted into the sacrum anteriomedially,anteriolaterally, unicortically and bicortically,and the insertion torque for each screw was measured Cyclic loading from 40 N to 400 N was applied to each screw at a frequency of 2 Hz up to 20 000 cycles Pull out tests were conducted after completion of the fatigue tests Results The average bone density at the S 1 body was 0 38 g/ml, and 0 24 g/ml at the S 1 ala The insertion torque and average pull out force following cyclic loading were significantly higher in bicortical fixation than that in unicortical fixation However, the pull out strength and insertion torque of medially oriented fixation was always higher than lateral fixation, regardless of whether the insertion was unicortical or bicortical The pull out force of unicortical and bicortical medial screw fixations following cyclic loading showed significant linear correlations with both the insertional torque and the bone mineral density of the S 1 body Conclusion In a group of young population, screw orientation(anterolateral or anteromedial) is more important in determining pull out strength than screw depth(unicortical or bicortical) following fatigue loading, anteromedially directed screws being significantly stronger than laterally placed screws Bone mineral density of the S 1 body and insertion torque are good preoperative and intraoperative indicators of screw pull out strength