两种长度的颈椎椎弓根螺钉与侧块螺钉拔出试验比较

目的:比较两种长度的颈椎椎弓根螺钉和侧块螺钉的抗拔出力,探讨颈椎经椎弓根短螺钉固定的可行性。方法:5具C3~C5共15节新鲜颈椎标本,用长度为28mm和20mm的皮质骨螺钉分别置入椎弓根,并用20mm的螺钉行侧块双皮质固定,螺钉进入侧块深度约14mm。行拔出试验,比较螺钉的最大轴向拔出力。结果:椎弓根长螺钉的最大拔出力为650N,椎弓根短螺钉为585N,两者比较无显著性差异(P>0.01);侧块螺钉的最大拔出力为360N,与椎弓根短螺钉比较有显著性差异(P<0.0001)。结论:颈椎椎弓根短螺钉固定可提供足够的稳定性,其安全性相对较高。

Pull-out strength of cervical pedicle short screws and pedicle long screws and lateral mass screws,a biomechanical comparison

Objective:To determine whether the poll-out strength of cervical short pedicle(20mm) screw is comparable with that of long pedicle(28mm) screw and whether it is significantly stranger than that of lateral mass screw.Method:15 fresh cervical specimens of 5 C3-C5 human cadaveric spinal segments and 3.5mm diameter cortical screws of 28mm and 20mm were used in this study.The screw placement were allotted as following: on each vertebrae of 5 specimens,28mm screw was inserted into pedicle on one side and 20mm screw into pedicle on the opposite side.On each vertebrae of another 5 specimens,28mm screw was inserted into pedicle on one side and 20mm screw was inserted into lateral mass on the opposite side.On each vertebrae of left 5 specimens,20mm screw was inserted into pedicle on one side and 20mm screw was inserted into lateral mass on the opposite side.Screws inserted into lateral mass were bicortical,and the actual working screw length defined as the millimeters of thread engaging bone was approxiamately 14mm.Each vertebrae was clamped in the custom-built jig,which was attached to a material testing machine.A coupling device that fit around the head of the screw was used to pull out each screw at a loading rate of 2mm/min.The arrangement was oriented so that the pull-out force was collinear with the long axis of the screw.The maximum axial pull-out strength was recorded.Result:The mean maximum pull-out strength was 650N for the 28mm pedicle screws,585N for the 20mm pedicle screws and 360N for the lateral mass screws.No significant difference was found between pull-out strength of 28mm and 20mm pedicle screws(P>0.01), however,short pedicle screws demonstrated a significantly higher resistance to the pull-out strength than the lateral mass screws(P<0.0001). Conclusion:The short pedicle screw fixation can provide enough stability while being relatively safer than long pedicle screw fixation.