Chiba M, McLain R F, Yerby S A, Moseley T A, Smith T S, Benson D R
Department of Orthopaedic Surgery, Tokai University, Kanagawa, Japan.
Spine (Phila Pa 1976). 1996 Feb 1;21(3):288-94. doi: 10.1097/00007632-199602010-00006.
This biomechanical study of fractures in cadaver vertebrae used specially designed pedicle screws to determine screw strains during loading of two different fixation constructs.
The authors determined the relative benefit of adding offset sublaminar hooks to standard pedicle screw constructs to reduce screw bending moments and prevent fixation failure and sagittal collapse.
Clinical studies have demonstrated a high incidence of early screw failure in short-segment pedicle instrumentation constructs used to treat unstable burst fractures. Strategies to prevent early construct failure include longer constructs, anterior strut graft reconstruction, and use of offset sublaminar hooks at the ends of standard short-segment pedicle instrumentation constructs.
Human cadaver spines with an L1 burst fracture were instrumented with a standard short-segment pedicle instrumentation construct using specially instrumented pedicle screws. Mechanical testing was carried out in flexion, extension, side bending, and torsion, and stiffness and screw bending moments were recorded. Offset hooks were applied initially, then removed and testing repeated. Stiffness data were compared to intact and postfracture results, and between augmented and standard constructs.
Addition of offset laminar hooks, supralaminar at T11 and infralaminar at L2, to standard short-segment pedicle instrumentation constructs increased stiffness in flexion by 268%, in extension by 223%, in side bending by 161%, and in torsion by 155% (all were significant except torsion). Sublaminar hooks also reduced pedicle screw bending moments to roughly 50% of standard in both flexion and extension (P < 0.05).
Supplemental offset hooks significantly increase construct stiffness without sacrificing principles of short-segment pedicle instrumentation, and absorb some part of the construct strain, thereby reducing pedicle screw bending moments and the likelihood of postyield deformation and clinical failure.
这项对尸体椎骨骨折的生物力学研究使用了专门设计的椎弓根螺钉，以确定两种不同固定结构加载过程中螺钉的应变情况。
作者确定了在标准椎弓根螺钉结构中添加偏置椎板下钩的相对益处，以减少螺钉弯矩并防止固定失败和矢状面塌陷。
临床研究表明，用于治疗不稳定爆裂骨折的短节段椎弓根器械固定结构中，早期螺钉失败的发生率很高。预防早期结构失败的策略包括使用更长的结构、前路支撑植骨重建，以及在标准短节段椎弓根器械固定结构的末端使用偏置椎板下钩。
对患有L1爆裂骨折的人体尸体脊柱使用专门的椎弓根螺钉进行标准短节段椎弓根器械固定。进行了前屈、后伸、侧弯和扭转的力学测试，并记录了刚度和螺钉弯矩。最初应用偏置钩，然后移除并重复测试。将刚度数据与完整和骨折后的结果进行比较，并在增强结构和标准结构之间进行比较。
在标准短节段椎弓根器械固定结构中，在T11处添加椎板上钩和在L2处添加椎板下钩，使前屈刚度增加268%，后伸刚度增加223%，侧弯刚度增加161%，扭转刚度增加155%（除扭转外均有统计学意义）。椎板下钩在屈曲和后伸时也将椎弓根螺钉弯矩降低至标准值的约50%（P < 0.05）。
补充偏置钩可显著增加结构刚度，而不牺牲短节段椎弓根器械固定的原则，并吸收部分结构应变，从而降低椎弓根螺钉弯矩以及屈服后变形和临床失败的可能性。
