Yuan Qiang, Han Xiaoguang, Han Xiao, He Da, Liu Bo, Tian Wei
*Department of Spine Surgery, Beijing Jishuitan Hospital, Fourth Clinical Medical College of Peking University, Beijing 10035, China.
Spine (Phila Pa 1976). 2014 Dec 15;39(26 Spec No.):B27-35. doi: 10.1097/BRS.0000000000000431.
To compare in detail the effects of pedicle screw insertion in osteoporotic vertebrae via Krag and Caudad trajectory techniques.
To compare the biomechanical stability of 2 pedicle screw fixation techniques and to correlate the stability of the pedicle screw with quantitative computed tomography (QCT).
Pedicle screw fixation is commonly used to facilitate fusion and postoperative rehabilitation. Fixation failure and loosening in the metal-bone interface are frequent, with osteoporosis usually a major factor. Pedicle screw fixation in osteoporotic spines is of particular concern regarding implant failure. Few reports have addressed which fixation method provides better biomechanical strength and thus presents less risk of failure.
Eleven cadaveric vertebrae were harvested and subjected to dual-energy x-ray absorptiometry and QCT to assess bone mineral density. Matched, polyaxial pedicle screws were inserted into the left and right pedicles of each vertebra. Screws were randomly assigned to the Caudad or Krag group by right or left side. They were inserted under 3-dimensional navigation system assistance. Cyclic loading tests were performed (maximum load 250 N, 3 Hz, up to 30,000 cycles) while recording load and displacement. Pullout tests were performed if the cyclic loading test was completed. Stiffness quotients were calculated.
Cycle-displacement curves showed more pedicle screw dislodgement in the Krag than the Caudad group (P < 0.01). Initially, stiffness was significantly higher in the Caudad group (P < 0.01), but the difference diminished thereafter. In the Caudad group, bone mineral density measured by QCT was significantly correlated with several biomechanical parameters.
Pedicle screws inserted in osteoporotic lumbar vertebrae using the Caudad trajectory displayed significantly higher biomechanical strength than those inserted using the Krag trajectory, especially during early fixation. Stability of pedicle screw fixation using the Caudad trajectory technique can be estimated by QCT.
详细比较经Krag技术和尾侧技术在骨质疏松性椎体中置入椎弓根螺钉的效果。
比较两种椎弓根螺钉固定技术的生物力学稳定性，并将椎弓根螺钉的稳定性与定量计算机断层扫描（QCT）相关联。
椎弓根螺钉固定常用于促进融合及术后康复。金属-骨界面的固定失败和松动很常见，骨质疏松通常是一个主要因素。骨质疏松性脊柱的椎弓根螺钉固定在植入失败方面尤其令人关注。很少有报告探讨哪种固定方法能提供更好的生物力学强度，从而降低失败风险。
获取11具尸体椎体，进行双能X线吸收法和QCT以评估骨密度。将匹配的多轴椎弓根螺钉分别置入每个椎体的左右椎弓根。螺钉通过右侧或左侧随机分配至尾侧组或Krag组。在三维导航系统辅助下进行置入。进行循环加载试验（最大载荷250 N，3 Hz，直至30000次循环），同时记录载荷和位移。若循环加载试验完成，则进行拔出试验。计算刚度系数。
循环位移曲线显示，Krag组的椎弓根螺钉移位比尾侧组更多（P < 0.01）。最初，尾侧组的刚度显著更高（P < 0.01），但此后差异减小。在尾侧组，QCT测量的骨密度与多个生物力学参数显著相关。
采用尾侧技术在骨质疏松性腰椎中置入的椎弓根螺钉，其生物力学强度显著高于采用Krag技术置入的螺钉，尤其是在早期固定期间。通过QCT可评估采用尾侧技术的椎弓根螺钉固定的稳定性。
