【作者】 刘达；

【导师】 雷伟；

【作者基本信息】 第四军医大学 ， 外科学， 2011， 博士

【摘要】 椎弓根螺钉技术已经成为脊柱外科最常用的内固定技术。随着我国人口老龄化的日益加剧,越来越多的骨质疏松(osteoporosis, OP)患者因脊柱疾病需要进行内固定手术。然而,OP严重影响钉骨界面的结合强度,使螺钉的把持力下降,常常导致螺钉松动、退出。因此,如何有效的提高OP条件下椎弓根螺钉的稳定性、防止螺钉松动已经成为脊柱外科亟待解决的难题。本课题组在前期设计出膨胀式椎弓根螺钉(expansive pedicle screw, EPS),研究表明EPS可以显著提高螺钉的稳定性,也可以有效的降低因增加螺钉的直径和长度带来的风险。有趣的是,通过文献回顾我们发现:尽管骨水泥(polymethylmethacrylate, PMMA)存在热损伤、渗漏和神经压迫等风险,但凭借其良好的机械强度和强化效果,PMMA仍然被广泛的用于OP条件下螺钉的强化处理。然而,在提高螺钉稳定性和优化钉道界面方面, EPS与传统的PMMA强化螺钉(polymethylmethacrylate-augmented pedicle screw, PMMA-PS)谁更具有优势呢?目前国内外还没有这方面的研究。目的:通过体外标本实验和动物体内实验比较EPS和PMMA-PS的稳定性和钉道界面情况,为EPS在临床上的广泛应用提供充分的理论依据。方法:1)体外实验部分:OP生物力学实验模块、OP尸体腰椎、离体绵羊腰椎均随机分为三组,对各组中的标本采用相同的方法制备钉道。普通椎弓根螺钉(conventional pedicle screw, CPS)组:直接拧入CPS;PMMA-PS组:向钉道内注入PMMA后再拧入CPS;EPS组:直接拧入EPS,插入内栓、压棒后拧紧螺帽。螺钉置入24小时后,对所有OP生物力学实验模块和OP尸体腰椎进行X线和CT检查,然后行轴向拔出实验;对离体绵羊腰椎进行轴向拔出实验、周期抗屈实验、micro-CT分析和组织学观察。2)体内实验部分:成功建立OP绵羊模型后,将绵羊腰椎(L1-L6)随机分为CPS组、PMMA-PS组和EPS组,置钉方法同离体绵羊腰椎实验部分。于术后3月和6月两个时间点各处死4只绵羊,行轴向拔出实验、micro-CT分析和组织学观察。结果:1)体外实验部分:X线检查和CT重建示,各组中螺钉位置均良好,未见PMMA渗漏现象,EPS均明显膨胀。①OP生物力学实验模块中,PMMA-PS组和EPS组的最大轴向拔出力(the maximum pullout strength, Fmax)和能量吸收值(energy absorbed to failure, E)均显著高于CPS组;而EPS组的Fmax和E均显著低于PMMA-PS组。②OP尸体腰椎中,PMMA-PS组和EPS组的Fmax和E均显著高于CPS组;而EPS组的Fmax和E与PMMA-PS组之间均无统计学差异。③离体绵羊腰椎中,PMMA-PS组和EPS组中螺钉的轴向稳定性和横向稳定性均显著强于CPS组,而EPS组的轴向稳定性和横向稳定性与PMMA-PS组之间均无统计学差异。CPS组中,骨组织直接包裹螺钉,形成了“螺钉-骨质”界面;PMMA-PS组中,PMMA严密包裹螺钉,分布在钉骨之间及钉道周围的骨髓腔内,阻碍了螺钉与骨质的直接接触,形成了“螺钉-PMMA-骨质”界面;EPS组中,骨小梁直接包裹螺钉,形成了“螺钉-骨质”界面。EPS的前端在椎体内明显膨胀,形成了一个“爪状”结构;螺钉前端胀开的两翼挤压周围的骨质,显著提高了局部的骨质密度。2)体内实验部分:①术后3月和6月,PMMA-PS组和EPS组的Fmax和E均显著高于同时间点的CPS组,而各时间点EPS组的Fmax和E与PMMA-PS组之间均无统计学差异。CPS组和PMMA-PS组的Fmax和E在术后3月和6月间的差异均无统计学意义,而EPS组术后6月的Fmax和E均显著高于3月。②术后3月和6月,CPS组中形成了“螺钉-骨质”界面。PMMA-PS组中形成了“螺钉-PMMA-骨质”界面。EPS组中形成了“螺钉-骨质”界面。EPS前端的“爪状”结构挤压并刺激局部的骨质生长,使局部的骨质条件(骨小梁数量和密度)在术后3月和6月均显著优于CPS组。从术后3月到6月,CPS组和PMMA-PS组中螺钉周围的骨质条件无明显变化,PMMA未发生降解、吸收,仍然存在于螺钉与周围骨质之间,形成了二次界面—“螺钉-PMMA-骨质”界面;而EPS膨胀部分周围的新生骨不断包裹螺钉并长入缝隙,显著改善了局部的骨质条件,螺钉与周围骨质形成良好的“螺钉-骨质”界面。结论:1) EPS可以显著提高骨质疏松条件下椎弓根螺钉的稳定性,并且达到了与传统的PMMA强化螺钉近似的固定强度。2) EPS可以形成良好的“螺钉-骨质”界面和钉道周围骨质条件,明显优于传统的PMMA强化螺钉,显著提高了螺钉在体内的远期稳定性。3) EPS可以有效的避免因使用PMMA可能带来的热损伤、渗漏和神经压迫等并发症。作为一种有效、安全和操作简便的方法,EPS具有在临床上广泛应用的巨大潜力。更多还原

【Abstract】 The pedicle screw instrumentation has become the most commonly used internal fixation techniques in spinal surgery. With growing aging of population in our country, more and more OP patients with spine disorders undergo spinal surgery with internal fixation. However, osteoporosis (OP) severely influenced binding strength of interface between screw and bone and decrasesed the holding force of screw, which usually resulted in loosening of screw, migration or back-out. Therefor, how to effectively increase stability of pedice screw in OP and prevent lossening of screw has become a pressing tough problem in spine surgery.In previous research, we designed an expansive pedicle screw (EPS) and it was proved that EPS can significantly improve screw stability and effectively reduce the risks caused by increasing diameter and length of screw. Intriguingly, we found from the related literatures that, in spite of risks of thermal injury, leakage and neurologic compression, PMMA is widely used for augmentation of screw in OP. However, there are no biomechanical and interfacial comparisons of the novel-designed EPS and traditional polymethylmethacrylate-augmented pedicle screw (PMMA-PS). Objective: To compare stability and interface of EPS and PMMA-PS through experiments in samples in vitro and in animal in vivo, and to provide sufficient theretical basis for wide application of EPS in clinic.Methods:1) Experiments in vitro. OP biomechanical tests blocks, OP cadaveric lumbar vertebrae, sheep lumbar vertebrae in vitro were all randomly divided into three groups. A pilot hole was prepared using the same method in samples in each group. The conventional pedicle screw (CPS) was inserted directly into the pilot hole in CPS group. In PMMA-PS group, the pilot hole was filled with PMMA followed by insertion of CPS. In EPS group, EPS was inserted directly into the pilot hole and the component elements were assembled to EPS. Twenty four hours after insertion of pedicle screw, X-ray and CT examination and axial pullout tests were performed to all OP biomechanical tests blocks and OP cadaveric lumbar vertebrae, and axial pullout tests, cyclic bending resistance tests, micro-CT analysis and histological observation were performed to all sheep lumbar vertebrae in vitro.2) Experiments in vivo. After successful establishment of OP sheep, sheep lumbar vertebrae (L1-L6) were randomly divided into CPS, PMMA-PS and EPS groups and treated with the same methods in experiment in sheep lumbar vertebrae in vitro. Four sheep were selected randomly and killed at two study periods of 3 months and 6 months after operation respectively and axial pullout tests, micro-CT analysis and histological observation were performed.Results:1) Experiments in vitro. No malpositioned screw and cement leakage were detected and all EPSs were obviously expanding in X-ray and CT examination.①In OP biomechanical tests block, the maximum pullout strength (Fmax) and energy absorbed to failure (E) in PMMA-PS and EPS groups were all significantly higher than those in CPS group, but Fmax and E in EPS group were all significantly lower than those in PMMA-PS group.②In OP cadaveric lumbar vertebrae, Fmax and EAV in PMMA-PS and EPS groups were all significantly higher than those in CPS group, but there were no significant differences in both Fmax and EAV between EPS and PMMA-PS groups.③In sheep lumbar vertebrae in vitro, both axial stability and vertical stability of screws in PMMA-PS and EPS groups were significantly enhanced compared with those in CPS group, but there were no significances on both axial stability and vertical screw stability between EPS and PMMA-PS groups. Bone trabeculae wrapped up the screw directly forming a“screw-bone”interface in CPS group. PMMA was found surrounding the screw totally and existing between screw and bone and in cavitas medullaris surrounded screw, which hampered the direct contact between bone and screw and formed a“screw-PMMA-bone”interface in PMMA-PS group. In EPS group, bone trabeculae wrapped up the screw directly forming a“screw-bone”interface. Anterior part of EPS presented an obvious expansion in vertebral body and formed a clawlike structure. The two fins pressed the surrounding bone tissue, which made local bone tissue more compacted and denser than that around anterior part of screw in CPS group.2) Experiments in vivo.①At 3-month and 6-month, Fmax and E in PMMA-PS and EPS groups were significantly higher than those in CPS group; however, there was no significant difference in both Fmax and E between EPS and PMMA-PS groups at two study periods. No significant differences were found in both Fmax and E in CPS and PMMA-PS groups between 3-month and 6-month, but Fmax and E in EPS group at 6-month were significantly higher than those at 3-month.②At 3-month and 6-month, bone trabeculae wrapped up the screw directly forming a“screw-bone”interface in CPS group. In PMMA-PS group, PMMA was found surrounding the screw totally and existing between screw and bone and in cavitas medullaris surrounded screw, which hampered the direct contact between bone and screw and formed a“screw-PMMA-bone”interface. In EPS group, bone trabeculae wrapped up the screw directly forming a“screw-bone”interface. Anterior part of EPS presented an obvious expansion and formed a clawlike structure. The two fins pressed and stimulated the growth of surrounding bone trabeculae, which made local bone condition (amount and density of bone trabeculae) significantly better than that in CPS group at 3-month and 6-month. From 3-month to 6-month, there were no obvious changes in the bone condition aound screw in CPS and PMMA-PS groups. PMMA was also found existing between bone and screw without any degradation and absorption, which formed a second interface-“screw-PMMA-bone”. Newly formed bone wrapped up the expanding part of EPS and grew into the interspace between two fins from 3 months to 6 months, which significantly improved the bone condition and formed a better“screw-bone”interface.Conclusions:1) EPS can significantly increase screw stability and obtain the similar fixation strength of traditional PMMA-augmented pedicle screw.2) EPS can form a significant better interface and bone condition around screw compared with traditional PMMA-augmented pedicle screw, which significantly improve long term stability of screw in vivo.3) EPS can effectively avoid complications caused by using of PMMA such as thermal injury, leakage and neurologic compression and so on. As an effective, safe and easy method, EPS has great potentiality on wide application in clinic.更多还原