Pfeiffer M, Hoffman H, Goel V K, Weinstein J N, Griss P
Department of Orthopaedics, Philipps University, Marburg, Germany.
Eur Spine J. 1997;6(4):249-55. doi: 10.1007/BF01322447.
The rigidity of a pedicle screw implant is a critical biomechanical variable in lumbar spinal fusions. Sufficient rigidity is required for integration of bone grafts and to promote healing. Osteopenia, stress shielding, and compensatory hypermobility have been described as consequences of excessive rigidity. Little is known about the biomechanical characteristics of "semirigid" compared to "rigid" implants. A new implant, whose rigidity can be varied by selection of different implant components, was tested in vitro under well-defined loading conditions. The three-dimensional load-displacement behavior of all lumbar vertebrae involved in or adjacent to the two-level fusion was evaluated for two fusion modifications: bilateral rigid and bilateral semirigid. Cyclic fatigue loading was subsequently carried out under realistic conditions and motion testing repeated. The rigid device reduced the motion of the L3-4 transfixed segment in the primary movement planes by 87.3% with respect to the intact spine value in flexion/extension (FE), 86.3% in lateral bending (LB), and 76.8% in axial rotation (AR). The semirigid device achieved a reduction in motion of 79.6% (FE), 82.7% (LB), and 51.7% (AR). The semirigid implant was particularly easy to insert, because no bending of rods or plates was necessary. The implants showed no loosening or breakage after the fatigue testing. The results are compared to other available systems and the underlying biomechanics discussed.
椎弓根螺钉植入物的刚度是腰椎融合术中一个关键的生物力学变量。骨移植融合及促进愈合需要足够的刚度。骨质减少、应力遮挡和代偿性活动过度已被描述为刚度过大的后果。与“刚性”植入物相比，关于“半刚性”植入物的生物力学特性知之甚少。一种新型植入物，其刚度可通过选择不同的植入部件来改变，在明确的加载条件下进行了体外测试。针对两种融合方式：双侧刚性融合和双侧半刚性融合，评估了两级融合中涉及的或相邻的所有腰椎椎体的三维载荷 - 位移行为。随后在实际条件下进行循环疲劳加载，并重复运动测试。刚性装置使L3 - 4固定节段在屈伸（FE）主运动平面内的运动相对于完整脊柱值减少了87.3%，在侧屈（LB）时减少了86.3%，在轴向旋转（AR）时减少了76.8%。半刚性装置实现的运动减少率分别为79.6%（FE）、82.7%（LB）和51.7%（AR）。半刚性植入物特别易于插入，因为无需对棒材或板材进行弯曲。疲劳测试后，植入物未出现松动或断裂。将结果与其他现有系统进行了比较，并讨论了其潜在的生物力学原理。
