【作者】 万世勇；

【导师】 雷伟；

【作者基本信息】 第四军医大学 ， 外科学， 2007， 硕士

【摘要】 椎弓根螺钉内固定技术广泛应用于治疗脊柱退行性病变、脊柱骨折、脊柱畸形、脊柱结核及椎体转移瘤等病症。椎弓根螺钉的固定可靠性取决于骨-螺钉界面把持力的维持。但对于骨质疏松症(osteoporosis,OP)患者,由于骨矿物质密度降低(bone mineral density,BMD),骨小梁变薄,骨-螺钉界面连接不牢固,常使患者面临着螺钉松动、固定失败的风险[1]。为强化椎弓根螺钉的稳定性,在钉道内添加聚甲基丙烯酸甲酯(polymethylmethacrylate,PMMA)、磷酸钙骨水泥(Calcium phosphate cement,CPC)、羟基磷灰石骨水泥(Hyduoyapatite cement,HAC)等强化物质可提高螺钉稳定性,相关的体外实验研究较多[4,5,6],但临床应用并不广泛。主要由于PMMA等存在诸多缺点[7,8],而CPC、HAC等在体内被完全替代之前的这段时间内是否可提供足够的力学强度,亦需进一步评价[5,6,9]。为了简化术中的强化操作过程,避免添加生物材料引起的并发症,本课题组前期的研究、设计了膨胀式椎弓根螺钉[2,3](expansive pedicle screw,EPS),并获专利保护(专利号: CN2647255)。离体的生物力学试验及机械强度试验,表明EPS在强度无下降的情况下,具有更高固定可靠性。但EPS在骨质疏松条件下,是否会实现长期的稳定及EPS的稳定机制仍不清楚,目前也无EPS界面研究的相关报道。研究目的:观察在骨质疏松状态下,EPS骨-螺钉界面以及EPS膨胀缝隙内组织学情况,探讨其在体强化稳定的作用机制,为临床应用进一步提供理论依据。研究方法:1)建立骨质疏松绵羊的动物模型。采用双侧卵巢切除法(ovariectomy,OVX)对绵羊去势。双能X-线吸收法(dual energy X-ray absorptiometry,DEXA)测定去势前、饲养1年后绵羊的BMD,并进行对比分析,确定本研究的OP绵羊的动物模型的建立。2)EPS在OP绵羊体内界面的显微CT(micro-computed tomography,Micro-CT)评价及组织学分析。植入EPS,饲养3个月、6个月后取材。采用最新的Micro-CT技术和包含螺钉的硬组织切片、染色技术,研究在OP的松质骨内EPS骨-螺钉界面以及EPS膨胀缝隙内的力学及组织学情况。研究结果:1)对标本的Micro-CT扫描及三维重建后,发现在EPS膨胀段骨-螺钉界面的骨小梁比界面外的骨小梁浓密,尤其在螺纹间更为明显,而在EPS非膨胀段的骨-螺钉界面的骨小梁稀疏,与周围骨质的浓密程度相似。在相同界值下取相同体积的与EPS螺纹相邻的“感兴趣区(regeon of interest,ROI)”进行骨计量学分析。扫描后的数据自动显示:EPS的膨胀段ROI的组织骨密度(tissure mineral density,TMD )和骨体积分数( bone volume fraction,BVF)、骨表面积体积比( bone surface /bone volume,BS/BV)、骨小梁厚度(trabecular thickness,Tb.Th)、骨小梁间隙( trabecular spacing,Tb.Sp)等骨小梁的三维参数,明显优于非膨胀段,经Mann-Whitney非参数检验,差异有统计学意义。2)切片镜下观察发现,EPS骨-螺钉界面及膨胀缝隙中的骨小梁与EPS紧密无缝隙相接触,界面无结缔组织层。新生骨小梁长入膨胀后的螺钉缝隙中,并与骨-螺钉界面的被压迫而致密化的松质骨相延续、一直延伸至膨胀中心部。结论: 1)EPS膨胀段对周围骨质持续的应力,使之变得更加致密,并改变了局部骨小梁的排列趋势,实现了EPS在骨质疏松状态下的早期机械性的稳定。2)EPS形成的“骨中有钉、钉中有骨”立体交叉复合体结构,实现了EPS在骨质疏松状态下的远期生物性的稳定。由于EPS具有独特的机械性稳定和生物性稳定的优点,对于需要进行脊柱融合内固定的骨质疏松患者,EPS是最佳的选择之一。更多还原

【Abstract】 Pedicle screws with plates or rods have been used to stabilize motion segments, correct spinal deformations and provide segmental fixation to promote graft incorporation in patients with degenerative, traumatic or neoplastic disorders of the spine. But pedicles screw fixation can be challenging in osteoporotic spine as mechanical stability of the pedicles screw-bone contract is affected by Bone mineral density (BMD). Poor rigidity of the bone-screw contract can lead to loosening of implant in osteoporotic patients. Analysis of pull-out strength of pedicles screw in lumbar spine has been performed in the past with a view to optimize the screw size, the screw insertion depth or direction and the screw design. Besides, to improve the strength of the screw-bone interface in osteoporosis (OP), mechanical tests have been performed with augmentation using polymethylmethacrylate (PMMA), Hydroxyapatite stick (HA), calciumphosphate cement (CPC), et al. These screw modification and augmentation strategies have been limited by possible complications and problems such as increased risks of pedicle fracture with resultant neural injury for larger screws, or anterior body penetration with ensuing vascular or visceral injury for longer screws, or potential problems associated with a non-absorbable foreign body in the spinal canal and with uncertain long-term rigidity on the course of substitution for those absorbable cements.To address these issues, we had designed expansive pedicle screws (EPS). EPS can improve bone fixation by increasing the screw tip diameter, allowing for greater bone contact without increasing screw diameter or length. Biomechanical studies have demonstrated that the use of an expansive screw design significantly improved the fixation strength compared with conventional pedicle screws. However, no systemic evaluation has been reported concerning the properties of screw-bone interface and the stable mechanism of EPS, especially in a living OP body.Objective To investigate the properties of the screw-bone interface and the stable mechanism of EPS in osteoporotic sheep, using three-dimensional (3D) imaging and reconstruction by micro-CT and histological analysis of microtome sections by microscope.Methods 1) Eves were ovariectomized bilaterally. Before ovariectomy(OVX)and 12 months after OVX, lumbar BMD was measured by dual energy X-ray absorptiometry(DEXA)to ensure the establishment of OP sheep model for this study.2) After EPS insertion in each femoral condyles of 6 OP sheep, 3 sheep were bred for 3 months, while another 3 sheep 6 months. Femoral condyles with EPS were 3D imaged and reconstructed by micro-CT. Histology was evaluated thereafter.Results 1) The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expansive section, especially within spiral marking. In the non-expansive section, however, there was no significant difference between the interface and the distant parts. The regions of interest (ROI) adjacent to EPS were reconstructed and analyzed by micro-CT using the same thresholds. The 3D parameters generated, including tissue mineral density (TMD), bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), in expensive sections were better than those in non-expensive sections. Each pair of these parameters was compared using Mann-Whitney analyses, and were considered statistically significant(P<0.05). 2) Histologically, newly formed bony trabeculae crawled along the expansive fissures and into the center of EPS. The newly-formed bones, as well as the bone at the bone-screw interface, closely contacted the EPS without connective tissue layer, it concluded that EPS had excellent biocompatibility, and they constructed four compartments and wrapped up the pins tightly.Conclusions 1) The fins’continuous pressure to the bony trabeculae of the expensive section ensured the EPS’s mechanical stabilization at earlier stage. 2) The special 3D structure, which bone contained pin as well as pin contained bone, kept on biological fixation and stiffness of EPS enduringly. EPS is one of the best chooses in OP patients for its special properties of mechanical stabilization and biological fixation, if segmental fixation of spine is needed.更多还原