Gao Mingxuan, Lei Wei, Wu Zixiang, Liu Da, Shi Lei
Department of Orthopaedics, Xijing Hospital, Fourth Military Medical University, No. 17 West Changle Road, Xi'an, Shaanxi Province, China.
Clin Biomech (Bristol). 2011 Mar;26(3):238-44. doi: 10.1016/j.clinbiomech.2010.10.008. Epub 2010 Nov 16.
The expansive pedicle screw was originally developed to be installed in the bone of compromised quality, but there are some concerns whether it can provide enough fixation strength in the spine with osteoporosis or severe osteoporosis.
Twelve fresh human cadaver spines were stratified into four levels: normal, osteopenia, osteoporosis and severe osteoporosis. The vertebra was bilaterally instrumented with pedicle screws according to four protocols, including conventional pedicle screw without augmentation, expansive pedicle screw without augmentation, conventional screw with augmentation and expansive screw with augmentation. Screw pullout tests were conducted.
Given the same specimen, the fixation strength of expansive screw was significantly higher than that of the conventional screw. When the same type of screw was used, the fixation strength of the calcium based cement augmented group was stronger than that of the non-augmented group. The pullout strength and stiffness of the expansive screw, augmented conventional screw and augmented expansive screw groups at the osteoporotic level were comparable to those of the conventional pedicle screw group at the osteopenic level. However, under the severely osteoporotic bone environment, the pullout strength of pedicle screw with whatever placement protocol was significantly lower than that of the conventional screw group at the osteopenic level.
Our results demonstrate that (i) the expansive pedicle screw appears feasible and safe in either osteopenic or osteoporotic spine; (ii) calcium based cement augmentation can offer improved initial fixation strength of pedicle screws.; and (iii) no screw placement protocol we examined is efficacious in the bone at the severely osteoporotic level.
膨胀椎弓根螺钉最初是为安装在质量受损的骨中而研发的，但对于其在骨质疏松或严重骨质疏松的脊柱中能否提供足够的固定强度存在一些担忧。
将12具新鲜人体尸体脊柱分为四个级别：正常、骨质减少、骨质疏松和严重骨质疏松。根据四种方案在双侧椎骨上植入椎弓根螺钉，包括未增强的传统椎弓根螺钉、未增强的膨胀椎弓根螺钉、增强的传统螺钉和增强的膨胀螺钉。进行螺钉拔出试验。
对于相同的标本，膨胀螺钉的固定强度显著高于传统螺钉。当使用同类型螺钉时，钙基骨水泥增强组的固定强度强于未增强组。骨质疏松级别下膨胀螺钉组、增强传统螺钉组和增强膨胀螺钉组的拔出强度和刚度与骨质减少级别下传统椎弓根螺钉组相当。然而，在严重骨质疏松的骨环境下，无论采用何种植入方案，椎弓根螺钉的拔出强度均显著低于骨质减少级别下的传统螺钉组。
我们的结果表明：（i）膨胀椎弓根螺钉在骨质减少或骨质疏松的脊柱中似乎可行且安全；（ii）钙基骨水泥增强可提高椎弓根螺钉的初始固定强度；（iii）我们所研究的任何螺钉植入方案在严重骨质疏松级别骨中均无效。
