骶骨S2椎弓根外进钉固定的生物力学分析

背景：模拟骶骨骨折S2椎弓根钉外进钉固定拔出力与在拔出椎弓钉时的应变电测分析鲜有报道。 目的：测量S2椎弓根外进钉固定拔出力与骶骨应变分布，为临床提供生物力学参数。 方法：取正常国人新鲜尸体骶骨标本，以椎弓根钉外进钉方法固定于S2椎弓根，以小型力传感器与椎弓根钉固定装置连接测量椎弓根钉的拔出力，同时以动静态电阻应变仪，对预先粘贴在4个椎弓根螺栓固定边缘部位和骶骨不同部位的应变片进行应变电测量。1号进钉点位置为左侧第1骶后孔下缘最低点，2号进钉点位置为右侧第1骶后孔下缘最低点，3号进钉点为左侧第1骶后孔连线与骶外侧嵴的交点，4号进钉点为右侧第1骶后孔连线与骶外侧嵴的交点。测量椎弓根螺钉最大拔出力和骶骨各测点应变值。 结果与结论：外进钉1号螺钉拔出力为(399.0±7.2) N，2号螺钉拔出力为(281.0±5.2) N，3号螺钉拔出力为(196.0±4.3) N，4号螺钉拔出力为(220.1±4.6) N。应变电测量最小应变发生在2号螺钉8号测点，应变为(13.5±1.1) με；最大应变发生在1号螺钉1号测点，应变为(96.8±6.5) με。提示S2椎弓根钉外进钉固定方法符合生物力学原理。

Biomechanical analysis about the pedicle screw fixation of S2 sacral fractures

BACKGROUND:Studies on surgery for sacral fracture and S2 sacral pedicle screw fixation have been conducted. However, the strain distribution rule of sacrum under maximum pulling-out force of S2 sacral pedicle screw is rarely reported. OBJECTIVE:To explore the pulling-out force of S2 sacral pedicle screw and the strain distribution of sacrum so as to provide biomechanical parameters for clinical fixation. METHODS: Fresh sacrum specimens from fresh corpses of normal people, with the method of S2 sacral pedicle screw fixation outside. The small sensors were connected to fixation device of pedicle screw to measure the tightening force of pedicle screw. At the same time, the electric strain on the strain gauge of different parts which was resistance to static and dynamic strain gauge pre-pasted on the four fixed-site edge of pedicle and the different parts of sacrum was measured using the resistance strain gauge. The entry point of screw 1 was the lowest point of the inferior margin of left first posterior sacral foramina; screw 2 was the lowest point of the inferior margin of right first posterior sacral foramina; screw 3 was the intersection point of left first posterior sacral foramina and lateral sacral crest; screw 4 was the intersection point of right first posterior sacral foramina and lateral sacral crest. Maximum pulling-out forces of pedicle screw and strain distribution values of the different points of sacrum were measured. RESULTS AND CONCLUSION:The screw pulling-out force of screws 1, 2, 3 and 4 were (399±7.2) N, (281.0±5.2) N, (196±   4.3) N, and (201±4.6) N, respectively. The minimum strain was found in the 8th measurement point of screw 2 (13.5±1.1) με, and the maximum strain was found in the 1st measurement point of screw 1 (96.8±6.5) με. These findings indicate that S2 sacral pedicle screw procedure accords with the biomechanical principle.