Liu Da, Zhang Yi, Lei Wei, Wang Cai-ru, Xie Qing-yun, Liao Dong-fa, Jiang Kai, Zhou Jin-song, Zhang Bo, Pan Xian-ming
*Department of Orthopaedics †Affiliated Stomatological Hospital, General Hospital of Chengdu Military Region, Chengdu, Sichuan Province ‡Department of Orthopaedics, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi Province, China.
J Spinal Disord Tech. 2014 Apr;27(2):E72-80. doi: 10.1097/BSD.0b013e318299f4b1.
Expansive pedicle screw (EPS) and polymethylmethacrylate-augmented pedicle screw (PMMA-PS) were inserted in sheep vertebrae in vitro and were evaluated by performing biomechanical tests, radiographic examinations and histological observations.
The objective of the study was to compare the biomechanical and interfacial performances of EPS and PMMA-PS in sheep lumbar vertebrae in vitro.
It is a great challenge for orthopedic surgeons performing transpedicular fixation in the osteoporotic spine. It was reported that either the EPS or PMMA-PS could increase the screw stability. However, there are no studies comparing the 2 kinds of screws especially in primary spinal instrumentation.
A total of 60 sheep lumbar vertebrae were randomly divided into 3 groups. A pilot hole was made in advance in all samples using the same method. Thereafter, the conventional pedicle screw (CPS) was inserted directly into the pilot hole in the CPS group; the hole in PMMA-PS group was first filled with polymethylmethacrylate (PMMA; 1.0 mL) and then inserted with CPS; and the EPS was inserted directly into the vertebrae in EPS group. After a period of 24 hours, biomechanical tests were performed to evaluate screw stability, and x-ray examination, micro-computerized tomography analysis, and histologic observation were performed to evaluate the interface between screw and bone.
Compared with the stability of CPS, those of EPS and PMMA-PS were significantly enhanced. However, no significant differences were detected between the stabilities of EPS and PMMA-PS. The PMMA surrounding the screw blocked direct contact between bone and screw and formed a "screw-PMMA-bone" interface in the PMMA-PS group. There was a "screw-bone" interface in both CPS and EPS groups. Nevertheless, the expanded anterior part of EPS formed a claw-like structure pressing the surrounding bone trabeculae, which made the local bone tissue more compacted and denser than that in the CPS group.
EPS can enhance the screw stability as markedly as the traditional PMMA-PS in primary surgery, and EPS can form a better immediate interface between screw and bone compared with PMMA-PS. EPS also can effectively avoid thermal injury, leakage, and compression caused by PMMA. A great feasibility was proved in this study to perform comparisons between the 2 kinds of pedicle screws in osteoporotic sheep vertebrae in vivo in the further research. In conclusion, we propose that EPS has a great application potential in augmentation of screw stability in the clinic.
将膨胀椎弓根螺钉（EPS）和聚甲基丙烯酸甲酯增强椎弓根螺钉（PMMA - PS）体外植入绵羊椎体，并通过生物力学测试、影像学检查和组织学观察进行评估。
本研究的目的是比较EPS和PMMA - PS在绵羊腰椎体外的生物力学和界面性能。
对于骨科医生在骨质疏松性脊柱中进行椎弓根固定是一项巨大挑战。据报道，EPS或PMMA - PS均可增加螺钉稳定性。然而，尚无研究比较这两种螺钉，尤其是在初次脊柱内固定方面。
将60个绵羊腰椎随机分为3组。所有样本均采用相同方法预先制作导向孔。此后，传统椎弓根螺钉（CPS）组将CPS直接插入导向孔；PMMA - PS组的孔先填充聚甲基丙烯酸甲酯（PMMA；1.0 mL），然后插入CPS；EPS组将EPS直接插入椎体。24小时后，进行生物力学测试以评估螺钉稳定性，并进行X线检查、微型计算机断层扫描分析和组织学观察以评估螺钉与骨之间的界面。
与CPS的稳定性相比，EPS和PMMA - PS的稳定性均显著增强。然而，EPS和PMMA - PS的稳定性之间未检测到显著差异。PMMA - PS组中螺钉周围的PMMA阻止了骨与螺钉的直接接触，并形成了“螺钉 - PMMA - 骨”界面。CPS组和EPS组均存在“螺钉 - 骨”界面。然而，EPS膨胀的前部形成了爪状结构压迫周围骨小梁，使得局部骨组织比CPS组更致密。
在初次手术中，EPS可与传统的PMMA - PS一样显著增强螺钉稳定性，并且与PMMA - PS相比，EPS可在螺钉与骨之间形成更好的即时界面。EPS还可有效避免PMMA引起的热损伤、渗漏和压迫。本研究证明了在进一步研究中对骨质疏松绵羊椎体体内的两种椎弓根螺钉进行比较具有很大的可行性。总之，我们认为EPS在临床增强螺钉稳定性方面具有很大的应用潜力。
