【作者】 高明暄；

【导师】 雷伟； 吴子祥；

【作者基本信息】 第四军医大学 ， 外科学， 2011， 博士

【摘要】 研究背景:经椎弓根内固定以其卓越三柱固定生物力学优势,已成为脊柱后路手术中最常用的内固定方式。其稳定性主要取决于椎弓根螺钉在骨质中的把持力,骨质疏松条件下螺钉的稳定性因受到骨质条件的影响而会显著下降。前期研究表明,膨胀式椎弓根螺钉可显著性提高螺钉抗拔出能力;但是,将其应用于什么程度的骨质疏松是安全的,这一问题仍未完全明了,本课题正是紧密围绕此实际问题而设计开展的。研究目的:一、评价不同骨质疏松条件下膨胀式椎弓螺钉的稳定性,以及螺钉稳定性是否可经一种新型钙基骨水泥强化提高。二、测量不同骨密度条件下椎体松质骨显微结构参数和力学特性指标,与螺钉拔出力作相关性分析,以了解与螺钉稳定性相关的骨显微结构和力学特性指标,进一步明确螺钉松动的原因。三、观察膨胀螺钉对合并有骨质疏松症的脊柱疾病的初步临床疗效,为进一步开展膨胀螺钉相关的临床试验提供理论和实践依据。材料方法:一、采用新鲜尸体脊柱标本,根据骨密度检测结果,按临床诊断标准分成骨质正常、骨量减少、骨质疏松和重度骨质疏松4个水平;设计分非强化普通钉、非强化膨胀钉、强化普通钉和强化膨胀钉4种方案进行植钉。用平衡不完全随机区组的统计学分组方法,对标本进行组间分配。每个骨密度水平,每种植钉方案植入螺钉9枚。然后,进行螺钉轴向拔出实验,测定最大拔出力、刚度和能量吸收值3项指标,对所测指标进行植钉方案间和骨密度水平间的纵横对比分析。二、收集螺钉拔出实验后未行强化钉道的椎体标本,在椎体中央部钻取松质骨柱状骨样,对骨样进行显微CT扫描、力学压缩实验,以获取椎体松质骨显微结构参数和力学特性指标。并作各项指标的不同骨密度水平间的比较分析,在了解这些指标随骨质疏松程度加重的变化规律的基础上,再将骨显微结构、力学特性指标与所对应的螺钉的最大拔出力作相关性分析。三、前瞻性设计,纳入合并有骨质疏松症的脊柱疾病患者共63例,在内固定手术治疗中应用膨胀式椎弓根螺钉。采用视觉模拟量表VAS、Oswestry功能障碍指数ODI、JOA腰椎评分等量表和影像学资料对临床疗效进行随访评价。观察内固定在位情况,计算骨性融合率。并对某一病种所特有的评价指标作专门测量统计;例如,对腰椎滑脱病例的影像学评价中要测量滑脱百分比Taillard指数,椎间隙平均高度,滑脱角及腰椎前凸角,以评价复位矫正和维持情况。结果:一、螺钉轴向拔出实验结果示:(1)骨密度水平相同条件下,膨胀螺钉的最大拔出力、刚度均显著性高于普通螺钉。(2)对同类型螺钉来说,采用新型钙基骨水泥强化可提高螺钉的最大拔出力,但是对提高螺钉拔出刚度无显著作用。(3)骨质疏松水平时,膨胀螺钉、强化普通钉以及强化膨胀钉组的最大拔出力至少可以达到骨量减少时普通钉的水平。(4)但是,重度疏松时,所有植钉方案的螺钉最大拔出力均显著下降,故在此骨质条件下没有任何一种植钉方案的最大拔出力能达到骨量减少时普通钉的水平。二、经椎体松质骨显微CT扫描、压缩实验发现:(1)随骨密度水平的依梯次下降,即骨质疏松程度进行性加重,椎体松质骨显微结构参数、力学特性指标随之发生相应明显变化,存在骨密度水平间的显著性差异。(2)广泛的相关性存在于骨密度、显微CT、压缩实验和螺钉拔出实验等指标之间。(3)其中普通螺钉和膨胀螺钉的最大拔出力均与显微CT扫描所得的骨体积分数BV/TV、骨小梁厚度Tb.Th和小梁间隙Tb.Sp呈高度相关关系,同时还与压缩实验中得出的极限应力σult和弹性模量E也高度相关。三、临床初步应用结果示:(1)纳入63例患者均获随访,平均随访时间约21.8月。(2)与术前相比,末次随访的VAS、ODI值下降依次72.9%和66.7%,JOA显效率、有效率依次为73.0%(46/63)和20.7%(13/63),总有效率为93.7%(59/63),三项指标术前与术后相比,均存在显著性差异。(3)末次随访影像学,所有63例病例,未见螺钉内固定的松动、断裂,内固定位置良好,成功骨性融合率为96.8%(61/63)。(4)其中8例腰椎滑脱,术后、随访Taillard指数,滑脱角和腰椎前凸角与术前相比均显著性下降,而椎间隙高度则显著性提高。结论:一、骨密度下降程度为骨量减少和骨质疏松时选用膨胀式椎弓根螺钉作内固定是安全的;新型钙基骨水泥强化可以进一步提高螺钉(包括膨胀螺钉)的抗拔出强度。二、随骨密度下降,骨组织会同时发生质的退变;螺钉的最大拔出力与部分骨显微结构参数、力学性能指标高度相关,检测这些指标能提高对螺钉发生松动风险的判断力。三、在合并有骨质疏松的脊柱疾病的内固定手术中,可以长时间维持稳定的固定,骨性融合率高,临床疗效良好。总结起来,本课题研究结果表明,骨质疏松条件下应用膨胀式椎弓根螺钉作固定,是安全有效的,也是理想选择之一。膨胀式椎弓根螺钉具有继续在临床上推广应用的广阔前景。更多还原

【Abstract】 Background The use of pedicle screw presents 3-D biomechanical advantages in the spine surgeries of internal fixation. These advantages depend on pedicle screws to retain bony purchase, which will be substantially compromised in the osteoporotic bone. Several previous studies have demonstrated that the fixation strength of pedicle screw can be significantly improved with an expansive design. However, there are some concerns whether this kind of pedicle screw, named expansive pedicle screw, is safe to use in the spine with osteoporosis or severe osteoporosis. Few studies are available to refer the performance of expansive pedicle screw used in the presence of osteoporosis or severe osteoporosis diagnosed according to the clinical criteria. Therefore, our study was initiated and performed in order to elucidate these concerns. Objectives The aim of this study is three-fold: (1) to evaluate whether the fixation strength of the expansive pedicle screw is competent in the human cadaver vertebrae with different levels of bone mineral density and whether the fixation strength can be further improved with the augmentation of a newly developed calcium-based biomaterial; and (2) to measure the micro-architectural indices and mechanical properties of cancellous bone in the vertebral body and to analyze the interrelationships between these parameters and the relationship between them and the corresponding maximum pullout strength of pedicle screws; and (3) to observe the efficacy of expansive pedicle screw in the management of spinal diseases coincided with osteoporosis and to preliminarily make sure of indications for the expansive pedicle screw fixation to provide theoretical and practical evidence for future clinical trials and extensive application of expensive pedicle screw in spine surgeries.Materials and Methods Fresh human cadaver spines were stratified into four levels: normal, osteopenia, osteoporosis and severe osteoporosis, according to the value of bone mineral density. The vertebra was bilaterally instrumented pedicle screws with four protocols, including conventional pedicle screw without augmentation, expansive pedicle screw without augmentation, conventional screw with augmentation and expansive screw with augmentation. The statistical method of“balanced incomplete randomized blocks”was used to assign the pedicles for the four protocols at the same level, resulting in nine screws per group per level. Screw pullout tests were conducted. On the load-stroke curve, the maximum pullout strength, stiffness and energy absorption were determined. The differences between the groups at the same bone mineral density level but different inserting protocols, or between the groups at different bone mineral density levels but same inserting protocol, were compared. Following the pullout tests, the vertebral specimens were collected. Subsequently, cancellous bone cylinders were drilled for micro-CT scanning and compression tests from 6 vertebrae in the groups without augmentation with the new biomaterial. The interrelationships between micro-CT, mechanical parameters themselves and the relationship between them and the corresponding maximum pullout strength of pedicle screws were analyzed. A preliminary clinical study was carried out with prospective design, in which 63 patients, who suffered from different spinal diseases and concurrent osteoporosis, were included. The questionnaires of VAS, ODI and JOA were administered preoperatively and at the latest follow-up to assess the clinical and functional outcomes. Also, the radiographic data were recorded, from which common observations such as the condition of pedicle screws, cage position and the fusion rate of bone graft were taken. Given special measurements were needed for one certain pattern of disease, they were gotten respectively. For example, in order to evaluate the orthopedic results in the treating of spondylolisthesis, the Taillard index (the degree of slip), the slip angle, the average disc height and the lumbar lordosis were measured on the lateral X-ray view pre-and post- operationally, and at follow-up.Results Given the same specimen, the maximum pullout strength and stiffness of expansive screw were significantly higher than those of conventional screw. When the same type of screw was used, the maximum pullout strength of the calcium based cement augmented group was higher than that of the non-augmented group, but the calcium based cement seemed to have very limited impact on improving the stiffness of either conventional or expansive pedicle screw. 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. With the increasing severity of osteoporosis, progressive bone volume loss, mechanical incompetence and micro-architectural deterioration were evident. Significant differences in micro-CT and mechanical parameters were found among the different levels of bone mineral density. Strong correlations were extensively observed among micro-CT or mechanical parameters themselves, between micro-CT indices and mechanical properties. The maximum pullout strength of the both pedicle screws highly correlated with bone volume over total volume (BV/TV), trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) from micro-CT scanning, and with ultimate stress (σult) and elastic modulus (E) from compression mechanical test. In the clinical trial, the 63 cases were all achieved to be followed up. The average follow-up time was about 22 months (rang 12-44 months) with the minimum of one year. Before surgery, the patients demonstrated severe pain and disability in term of preoperative VAS and ODI. At follow-up assessment, the clinical and functional outcome showed significant improvement in all measurements. The mean VAS and ODI scores were significantly decreased by 72.9% and 66.7%, respectively. According to the results of JOA, an obvious efficacy was shown in 73.0% patients and a moderate efficacy was in 20.7%, so the total effective rate was 93.7 (59/63). Significant differences were found in all the three questionnaire scores between pre-operation and follow-up. There were no instances of screw loosening, pullout, or breakage of the expansive pedicle screws. No measurable subsidence or extrusion of the cages was evident at the follow-up evaluation. According to the radiographic evidence taken at the last follow-up, 61 out of 63/all cases achieved the criteria of solid fusion and the fusion rate is 96.8%. For the eight cases of spondylolisthesis, post-operatively the average slip percentage (Taillard index), slip angle and angle of lumbar lordosis were significantly decreased and the average disc height was significantly improved compared to those of pre-operation. In addition, no significant differences in these measurements were found between post-operation instantly and at the final follow-up.Conclusions Our pullout test results demonstrate that the expansive pedicle screw appears feasible and safe in either osteopenic or osteoporotic spine and that calcium based cement augmentation can further improve the initial fixation strength of expansive pedicle screw. The maximum pullout strength of the pedicle screws highly correlated with some parameters from micro-CT scanning and compression mechanical test. To measure these parameters can help to improve the prediction of the fixation strength of pedicle screw. The preliminary clinical trial has shown that the application of expansive pedicle screw in operative managing spinal diseases with concomitant osteoporosis is a feasible and reliable alternative. This fixation technique can create a favorable biomechanical condition to obtain a solid fusion and to produce good clinical results.In summery, all the results of this study reveal that the expansive pedicle screw is valuable to apply in spine surgery, especially in the presence of osteoporosis.更多还原