Investigation of the mechanical interaction of the trabecular core with an external shell using rapid prototype and finite element models

The mechanical properties of vertebral bone have been widely studied with the ultimate goal of improving fracture risk prediction. However, the mechanical interaction between the cortical shell and the trabecular core is not well understood. The objective of this study was to investigate this interaction and to determine what effect it has on the ultimate strength of the whole bone. This objective was achieved by compression testing rapid prototype (RP) models of cylindrical trabecular bone cores, with and without an integral surrounding shell and incorporating increasing levels of artificially induced bone loss. Corresponding finite element (FE) models were generated and the load sharing of the shell and trabecular core was analysed under linear elastic loading conditions. The results of the physical RP model tests and corresponding FE analyses indicated that there was a reinforcing effect between the cortical shell and the trabecular core for all models tested and that the reinforcing effect became relatively more important to the ultimate strength of the whole bone as the bone volume fraction of the trabecular core decreased. It was found that two mechanisms contributed to the reinforcing effect: (i) load transfer from the highly stressed shell into the connecting outer trabeculae of the core for the shelled model. This did not occur for the un-shelled model where the load dropped off at the outer unsupported trabeculae; (ii) the stiffening effect on the shell due to the support provided by the connecting struts of the trabecular core, which serves to inhibit bending and buckling behaviour in the shell under compression loading. It was found that the stiffening on the shell was the more dominant contributor to the overall reinforcing effect between the shell and the trabecular core.     

Prophylactic vertebroplasty can decrease the fracture risk of adjacent vertebrae: An in vitro cadaveric study

Adjacent level vertebral fractures are common in patients with osteoporotic wedge fractures, but can theoretically be prevented with prophylactic vertebroplasty. Previous tests on prophylactic vertebroplasties have been performed under axial loading, while in vivo changes in spinal alignment likely cause off-axis loads. In this study we determined whether prophylactic vertebroplasty can also reduce the fracture risk under off-axis loads.In a previous study, we tested vertebral bodies that were loaded axially or 20° off-axis representing vertebrae in an unfractured spine or vertebrae adjacent to a wedge fracture, respectively. In the current study, vertebral failure load and stiffness of our previously tested vertebral bodies were compared to those of a new group of vertebral bodies that were filled with bone cement and then loaded 20° off-axis. These vertebral bodies represented adjacent-level vertebrae with prophylactic bone cement filling.Prophylactic augmentation resulted in failure loads that were comparable to those of the 0° group, and 32% greater than the failure loads of the 20° group. The stiffness of the prophylacticly augmented vertebrae was 21% lower than that of the 0° group, but 27% higher than that of the 20° group. We conclude that prophylactic augmentation can decrease the fracture risk in a malaligned, osteoporotic vertebra. Whether this is enough to actually prevent additional vertebral fractures in vivo remains subject of further study.     

Tissue-level failure accumulation in vertebral cancellous bone: a theoretical model.

Vertebral compression fractures are a potentially severe injury, which is characteristic to osteoporotic elderly. Despite being a significant healthcare problem, the etiology of compression fractures is not fully understood, and there are no biomechanical models in the literature that describe the development of these fractures based on cancellous bone failure accumulation. The objective of this study was therefore to develop a computational model of tissue-level failure accumulation in vertebral cancellous bone, which eventually leads to compression fractures. The model predicts the accumulated percentage of broken trabeculae delta in a vertebral region of interest (ROI) over 60 years, by employing Euler's theory for elastic buckling. The accumulated failure delta is calculated as function of the daily activity characteristics and rate of annual bone loss (RABL) with aging. An RABL of unity represents the normal bone loss attributed to aging per se, whereas RABL>1 is assumed to represent pathological bone metabolism such as osteoporosis. Simulations were conducted for a range of RABLs, to determine the effect of changes in bone metabolism on the accumulation of bone failure. Results showed that bone failure rapidly increased with RABL. Generally, trabecular failure was shown to become more severe for RABL>4. Total failure was exhibited at RABL=7.5 for the central ROI, and at RABL=8.5 for the sub-endplate ROI. We concluded that vertebral compression fractures advance monotonically between the age of 50-55 years and 70 years, and may accelerate thereafter if RABL is high (~8). Additionally, the model identified weight lifting as the action that most dramatically accelerated the destruction of osteoporotic spinal cancellous bone. The present biomechanical model is useful for understanding the etiology of compression fractures, and potentially, depending on further experimental characterization of RABL, for considering the effects of medications that influence bone metabolism on patient prognosis.     

In silico evaluation of stress distribution after vertebral body augmentation with conventional acrylics, composites and glass polyalkenoate cements

There exists clinical evidence of fractures in adjacent vertebrae subsequent to vertebral augmentation procedures, such as vertebroplasty (VP) and kyphoplasty (KP). A potential contributory factor to such fractures may be the excessive mismatch of mechanical properties between contemporary bone cements (i.e. polymethyl methacrylate (PMMA) and bisphenol-a-glycidyl dimethacrylate (BIS-GMA)) and bone. Aluminum-free glass polyalkenoate cements (GPCs) present an interesting alternative to conventional bone cements. GPCs adhere to the philosophy that implant materials should have mechanical characteristics similar to those of the bone, and also offer chemical adhesion and intrinsic bioactivity. However, their influence on the loading patterns of augmented vertebrae (as compared with conventional bone cements) is not available in the literature. The present work investigates how the moduli of PMMA, BIS-GMA and GPC implants affect the stress distribution within a single, augmented vertebra, in both healthy and osteoporotic states. Using a finite element model of the L4 vertebra derived from computed tomography data, with simulated augmentation, it was found that, as cement stiffness increased, stress was redistributed from the cortical and trabecular bone to the cement implant. The GPC implant exhibited the least effect on stress redistribution in both the healthy and osteoporotic models compared to its acrylic counterparts. The significance of this work is that, under simulated physiological loading conditions, aluminum-free GPCs exhibit stress distribution throughout the vertebral body similar to that of the healthy bone. In comparison to conventional augmentation materials, the use of aluminum-free GPCs in VP and KP may help to ameliorate the clinical complication of adjacent vertebral body compression fractures.     

Development of a multi-scale finite element model of the osteoporotic lumbar vertebral body for the investigation of apparent level vertebra mechanics and micro-level trabecular mechanics

Osteoporotic spinal fractures are a major concern in ageing Western societies. This study develops a multi-scale finite element (FE) model of the osteoporotic lumbar vertebral body to study the mechanics of vertebral compression fracture at both the apparent (whole vertebral body) and micro-structural (internal trabecular bone core) levels. Model predictions were verified against experimental data, and found to provide a reasonably good representation of the mechanics of the osteoporotic vertebral body. This novel modelling methodology will allow detailed investigation of how trabecular bone loss in osteoporosis affects vertebral stiffness and strength in the lumbar spine.     

骨质疏松骨折椎体及相邻椎体骨水泥注入前后的有限元分析

背景：目前有限元构建模型主要是基于医学图像的建模方法,骨水泥注入主要是人为假设的,而文章中治疗前后的数据直接来源于CT扫描,可靠性更高。 目的：构建骨水泥注入前后骨质疏松性腰椎骨折椎体的三维有限元模型,分析治疗前后病椎及邻椎的应力变化。 方法：选取1例75岁骨质疏松性L₂椎体压缩性骨折患者,经双侧椎弓根注入少量骨水泥获得良好疗效,随访2年病椎及邻椎无新发骨折,局部无疼痛。根据其治疗前后的腰椎CT数据,构建三维有限元模型,模拟腰椎屈伸、左右侧屈、旋转等运动,统计分析治疗前后同一运动状态下的应力变化。 结果与结论：建立了腰椎压缩骨折骨水泥注入前后的三维有限元模型,共生成222 727个单元。骨水泥注入增加了L₂椎体(病椎)屈、伸、侧屈各运动时的应力(P < 0.05),对其旋转时的应力无明显影响(P > 0.05);对L₁,L₃椎体(邻椎)在屈、伸、侧屈及旋转时的应力亦无影响(P > 0.05)。提示少量骨水泥注入治疗老年骨质疏松性腰椎骨折可增加病椎强度及应力,但不改变相邻椎体应力。     

椎体成形穿刺注射骨水泥防止灾难性并发症：87例137个椎体资料分析

背景：椎体成形治疗老年骨质疏松椎体压缩性骨折效果确切,但一些热点问题仍无定论。 目的：探讨椎体成形技术治疗老年骨质疏松椎体压缩性骨折过程中穿刺损伤、骨水泥注射剂量、多椎体成形及骨水泥渗漏等问题的解决方案。 方法：回顾性分析经皮穿刺椎体成形技术治疗骨质疏松椎体压缩性骨折87例137个椎体。全部经单侧椎弓根穿刺,骨水泥稀薄期注射,骨水泥注射量为3~7.5 mL,胸椎3 mL以上,腰椎4.5 mL以上,平均4.8 mL,多椎体者均一次手术完成。 结果与结论：随访6~30个月,治疗后第2天和最终随访时患者目测类比疼痛评分及Oswestry功能障碍指数评分均显著低于治疗前(P < 0.01)。所有患者胸腰背疼痛明显缓解,其中58例疼痛完全消失;1例术中出现骨水泥单体中毒症状,28例出现不同程度骨水泥渗漏,但未出现临床症状。137个椎体中骨水泥渗透达到和超过中线119个,占87.2%。提示椎体成形技术是治疗老年骨质疏松椎体压缩性骨折的有效方法。骨水泥稀薄期注射能够获得良好的渗透效果;在局麻药限量范围内,一次可完成3个以上椎体成形;严格正规的操作技术是预防骨水泥渗漏灾难性并发症最重要的方法。     

基于CT多平面重建及MRI分析新鲜骨质疏松性椎体压缩骨折椎体内骨折区域形态类型及分布规律

文题释义： 骨质疏松症：是一种以骨量低下、骨微结构破坏导致骨脆性增加，易发生骨折为特征的全身性骨病。骨质疏松症分为原发性和继发性2大类，原发性骨质疏松症又分为绝经后骨质疏松症、老年性骨质疏松症和特发性骨质疏松症3种。继发性骨质疏松症通常由后天多种因素(物理、力学、化学)或疾病所致。双能X射线骨密度T值≤-2.5SD即可诊断为骨质疏。 胸、腰椎体压缩性骨折的诊断：胸、腰椎体压缩性骨折是骨质疏松常见并发症之一，X射线是诊断胸、腰压缩性骨折的首选检查方式，其有利于观察脊柱序列的连续性，可同时观察整个胸腰段以及更多椎体受伤情况，例如椎体的高度、宽度、楔形改变以判断骨折压缩的程度，但难以显示骨细微结构变化。CT检查可从冠状面、矢状面、横断面显示椎体三柱情况，但对椎管内外软组织显示不如MRI。MRI可有效鉴别陈旧及新鲜椎体压缩性骨折，同时可鉴别椎体良性及恶性病变；此外，MRI对于脊髓、神经损伤、椎管内病变等准确性高于CT，但显示骨折线、小关节骨折或脱位等不及CT。 背景：既往有学者根据X射线、MRI等对骨质疏松性椎体压缩骨折进行分类，然而目前国内外关于骨质疏松性椎体压缩骨折中椎体内骨折区域的形态类型及分布规律的研究鲜有报道。 目的：应用CT多平面重建及MRI观察并总结新鲜骨质疏松性压缩骨折椎体内的骨折区域形态类型及分布规律。 方法：回顾性分析2011年9月至2017年6月广州中医药大学第一附属医院收治的352例骨质疏松性椎体压缩骨折患者的临床资料，其中男69例，女283例，平均年龄73.07岁。入院后所有患者完善X射线、CT多平面重建、MRI及骨密度等检查，根据患者临床症状及影像学检查确诊477个椎体为新鲜骨质疏松性压缩骨折。将多平面重建CT中致密影或透亮线及MRI中骨髓水肿带定义为骨折区域，由2名脊柱外科医师及1名影像科医师通过多平面重建CT及MRI观察并总结骨折区域的形态类型及分布规律。研究已获得广州中医药大学第一附属医院伦理委员会批准，批准号：ZYYECKYJ【2017】057。 结果与结论：①MRI可清晰显示472个椎体内骨折区域，不能清晰显示5个椎体内骨折区域；多平面重建CT可清晰显示469个椎体内骨折区域，不能清晰显示8个椎体内骨折区域，其中包括MRI中无法分析骨折区域的5个椎体；两种检查方法观察骨折椎体内骨折区域无明显差异(P=0.402)，最终发现8个椎体不能通过CT或MRI判断其骨折区域形态；②以矢状面CT、MRI图像为主观察469个椎体，骨折区域形态类型分为嵌插型(n=311，66.31%)和裂隙型(n=158，33.69%)，在裂隙型椎体中，26个椎体裂隙内含有气体，28个椎体裂隙内含有液体，7个椎体裂隙内同时存在气体和液体；③以矢状面CT、MRI图像为主观察469个椎体，骨折区域在椎体内的分布位置分为上方型(n=238，50.75%)、下方型(n=80，17.06%)、前方型(n=21，4.48%)、中央型(n=110，23.45%)、混合型(n=20，4.26%)；④结果表明，结合多平面重建CT及MRI能有效辨别椎体内骨折区域形态类型及明确骨折区域在椎体内分布情况，这对于分析新鲜骨质疏松性椎体压缩骨折受伤机制及制定治疗方案有一定的指导意义。 ORCID: 0000-0002-2990-7592(莫凌) 中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程     

n-HA/PA66椎体增强器和椎体成形术治疗骨质疏松性椎体骨折的生物力学效果对比

目的对比研究n-HA/PA66椎体增强器和椎体成形术治疗骨质疏松性骨折椎体的生物力学效果,并为临床上选择n-HA/PA66椎体增强器的入路方式和数量提供理论依据。方法在正常椎体T11～L3有限元模型的基础上,建立4种增强器-椎体T11～L3有限元模型(横突入路A、横突入路B、腰大肌入路A和腰大肌入路B)、两种删除椎体横突间韧带的对照组模型,以及两种骨水泥-椎体T11～L3有限元模型(1.8、3.6 mL骨水泥)。在9种有限元模型上均施加500 N垂直荷载和7 N·m不同方向力矩,计算分析模型在垂直、前屈、后伸、侧弯和扭转工况下的应力和位移,并基于计算结果探究两种不同骨质疏松性椎体骨折治疗方法对椎体的生物力学影响。结果在相同荷载工况下,注入骨水泥后椎体的应力较植入增强器后椎体的应力增加更大,且位移减量更小。4种增强器-椎体T11～L3有限元模型中,采用腰大肌入路A方式(即经腰大肌单侧植入1枚增强器)植入增强器使得椎体应力增加最小。结论为了降低应力增加而引起再次骨折的风险,同时增强骨折椎体的刚度,建议临床医生应优先采用经腰大肌单侧植入1枚增强器来治疗骨质疏松性椎体骨折。     

Biomechanical effects of cement filling location on osteoporotic vertebral compression fracture: A three-dimensional finite element analysis北大核心

BACKGROUND: When bipedicular percutaneous vertebral augmentation is performed for osteoporotic vertebral compression fractures, three types of cement filling location in the vertebral body are commonly seen, including anterolateral, anteromedial, and posterolateral, especially in lumbar spine with big volume of vertebral bodies. At present, no relevant biomechanical research has been found to compare the impact of these three bone cement filling locations on the biomechanical properties of fractured vertebral bodies. OBJECTIVE: To analyze and compare biomechanical effects of three types of cement filling location on osteoporotic vertebral compression fracture using threedimensional finite element analysis method. METHODS: Osteoporotic L1-L5 three-dimensional finite element model was constructed and osteoporotic vertebral compression fractures model was simulated in L3. Three types of cement filling location, including anterolateral, anteromedial, and posterolateral, were simulated in osteoporotic vertebral compression fractures model, respectively. Four models were got for the test eventually. Maximum von Mises stress of L3 veretebral body and maximum displacement of L3 fractured area were calculated for the four models under the same loading conditions, including flexion, extension, lateral bending, and rotations. RESULTS AND CONCLUSION: (1) Under flexion, maximum von Mises stress of L3 veretebral body in anterolateral, anteromedial, and posterolateral sites was about 18.31%, 19.43%, and 28.31% of that in osteoporotic vertebral compression fractures model, respectively. Maximum displacement of L3 fractured area was about 13.92%, 16.49%, and 29.90% of that in osteoporotic vertebral compression fractures model, respectively. Therefore, compared with percutaneous vertebral augmentation pre-operation, maximum von Mises stress and maximum displacement were decreased significantly after percutaneous vertebral augmentation, with those in anterolateral site being decreased the most significantly. Similar changes could be seen in extension, lateral bending, and rotations loading conditions. (2) The results showed that anterolateral cement filling could better restore strength and stability of fractured vertebral body. To make cement fill in the anterolateral fractured area first using precise puncture and cement injection technique is suggested. © 2022, Publishing House of Chinese Journal of Tissue Engineering Research. All rights reserved.     

经皮椎体成形高黏度骨水泥注入修复老年椎体压缩骨折：椎体高度恢复评价

背景：在应用高黏度骨水泥以及椎体成形修复骨质疏松性椎体压缩骨折的过程中,骨水泥的推注量-压缩椎体高度的恢复-临床疗效”之间是否存在必然联系以及内在的规律,目前缺乏此方面的循证医学证据,且存在一定争议。 目的：观察经皮椎体成形高黏度骨水泥注入修复老年骨质疏松椎体压缩性骨折的椎体高度恢复情况。 方法：选取2011年1月至2012年12月新疆维吾尔自治区中医医院脊柱外科收治的骨质疏松压缩性骨折老年患者110例,共139椎,均由同一组外科医生采用经皮椎体成形治疗,在骨水泥拉丝期时在“G”形臂监视下将高黏度骨水泥注入骨折椎体内。治疗后随访12个月,以目测类比评分、Barthel指数、椎体高度恢复为观察评价指标。 结果与结论：110例患者共139椎,修复过程顺利,单个椎体骨水泥平均注入量为3-6 mL,平均3.5 mL。患者的目测类比评分由治疗前平均7.9分降到了治疗后12个月的平均1.8分;Barthel指数治疗前平均为40.25,治疗后12个月时为82.21,治疗后与治疗前比较目测类比评分和Barthel指数均有明显改善(P < 0.05)。治疗后139个椎体前、中部的高度增加到了原椎体高度的(81.25±9.26)%和(78.22±10.65)%,治疗后24 h、3个月、12个月与治疗前相比椎体前部、中部高度均有显著恢复(P < 0.05)。治疗后通过随访观察发现,发生高黏度骨水泥渗漏的椎体有5个,以上患者未出现临床症状,未发生神经损伤或肺栓塞等严重并发症。提示经皮椎体成形高黏度骨水泥注入修复骨质疏松性椎体压缩性骨折的过程中,不仅可以有效缓解患者疼痛,在不同程度上恢复压缩椎体的高度,而且并发症发生率低,患者恢复时间短。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程     

Vertebral Osteoporosis and Trabecular Bone Quality

Vertebral fractures due to osteoporosis commonly occur under non-traumatic loading conditions. This problem affects more than 1 in 3 women and 1 in 10 men over a lifetime. Measurement of bone mineral density (BMD) has traditionally been used as a method for diagnosis of vertebral osteoporosis. However, this method does not fully account for the influence of changes in the trabecular bone quality, such as micro-architecture, tissue properties and levels of microdamage, on the strength of the vertebra. Studies have shown that deterioration of the vertebral trabecular architecture results in a more anisotropic structure which has a greater susceptibility to fracture. Transverse trabeculae are preferentially thinned and perforated while the remaining vertical trabeculae maintain their thickness. Such a structure is likely to be more susceptible to buckling under normal compression loads and has a decreased ability to withstand unusual or off-axis loads. Changes in tissue material mechanical properties and levels of microdamage due to osteoporosis may also compromise the fracture resistance of vertebral trabecular bone. New diagnostic techniques are required which will account for the influence of these changes in bone quality. This paper reviews the influence of the trabecular architecture, tissue properties and microdamage on fracture risk for vertebral osteoporosis. The morphological characteristics of normal and osteoporotic architectures are compared and their potential influence on the strength of the vertebra is examined. The limitations of current diagnostic methods for osteoporosis are identified and areas for future research are outlined.     

Mechanical evaluation by patient-specific finite element analyses demonstrates therapeutic effects for osteoporotic vertebrae

Osteoporosis can lead to bone compressive fractures in the lower lumbar vertebrae. In order to assess the recovery of vertebral strength during drug treatment for osteoporosis, it is necessary not only to measure the bone mass but also to perform patient-specific mechanical analyses, since the strength of osteoporotic vertebrae is strongly dependent on patient-specific factors, such as bone shape and bone density distribution in cancellous bone, which are related to stress distribution in the vertebrae. In the present study, patient-specific general (not voxel) finite element analyses of osteoporotic vertebrae during drug treatment were performed over time. We compared changes in bone density and compressive principal strain distribution in a relative manner using models for the first lumbar vertebra based on computer tomography images of four patients at three time points (before therapy, and after 6 and 12 months of therapy). The patient-specific mechanical analyses indicated that increases in bone density and decreases in compressive principal strain were significant in some osteoporotic vertebrae. The data suggested that the vertebrae were strengthened structurally and the drug treatment was effective in preventing compression fractures. The effectiveness of patient-specific mechanical analyses for providing useful and important information for the prognosis of osteoporosis is demonstrated.     

骨质疏松椎体压缩性骨折患者脊柱矢状面的失平衡

背景：国内外总结脊柱失平衡的原因包括脊柱畸形、脊柱退变性疾病、骨质疏松椎体压缩性骨折等,作者通过临床研究认为动力性因素(腰背肌)在脊柱矢状面失平衡中起关键作用。 目的：通过观察骨质疏松椎体压缩性骨折患者的临床表现和治疗效果,分析脊柱矢状面失平衡的原因。 方法：回顾性分析2012年1月至2013年5月收治的骨质疏松压缩性骨折伴脊柱矢状面失平衡患者41例,均在局麻下行经皮穿刺球囊扩张椎体成形治疗。治疗前患者均行骨密度、站立位全脊柱正侧位X射线、以伤椎为中心的CT及MR检查。于患者站立位全脊柱正侧位片中测量伤椎前缘高度、脊柱后凸Cobb角及改善角度、伤椎楔形变角度及改善角度;要求患者行负重试验及行走试验,对比治疗前后数据。 结果与结论：治疗前患者出现脊柱矢状面失平衡症状所需行走的距离显著短于治疗后(P < 0.05);治疗前出现脊柱矢状面失平衡负重试验时间亦显著短于治疗后(P < 0.05)。在治疗前后站立位全脊柱正侧位片中,Cobb角的平均差值为(10.01±0.76)°,椎体楔形变改善的平均差值为(4.84±0.40)°,差异有显著性意义(P < 0.05)。所有患者均获随访,患者腰背部疼痛及矢状面失平衡症状明显缓解。所有患者行经皮球囊扩张椎体成形治疗后无严重并发症发生。提示骨质疏松压缩性骨折部分患者会出现脊柱矢状面失平衡症状,原因并非伤椎楔形变单一因素所致。且患者通过经皮球囊扩张后凸成形治疗后,失平衡症状往往会明显改善,提示脊柱骨折后腰痛限制腰背肌力量是导致脊柱矢状面失平衡的一个重要原因。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程全文链接：     

骨水泥注射体积与骨质疏松压缩性骨折椎体及邻近椎体应力的关系

背景：椎体成形及椎体后凸成形可有效修复骨质疏松性椎体压缩性骨折,但术后可引起骨折椎体及邻近椎体应力改变易导致新发骨折。 目的：应用三维有限元法分析椎体成形不同体积骨水泥注射后骨折椎体及邻近椎体的应力变化。 方法：选取1例有代表性的健康成年男性志愿者行腰椎CT扫描,将图像处理后导出应用Mimics进行三维重建,应用Geomagic对三维模型进行光滑、打磨、去噪,Ansys Workbench下装配实体模型,赋值后建立L2-L4段骨质疏松椎体压缩性骨折模型。设定在L3椎体注入分别1 mL、2 mL、4 mL、6 mL骨水泥,骨水泥在椎体中央呈球形分布。在L2上表面施加500 N预载荷,附加弯矩为50 N•m,约束L4下表面自由度。模拟L2-L4前屈、后伸、右屈及右侧轴向旋转4种运动状态,比较不同体积骨水泥注射前后骨折椎体及上下邻近椎体的应力变化。 结果与结论：骨折椎体及邻近椎体应力骨水泥注射后均较注射前明显增加,并随骨水泥注入量的增加骨折椎体及邻近椎体承受的应力也随之增大,其可能是导致邻近椎体骨折的因素之一。 中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程      

Vibrational testing of trabecular bone architectures using rapid prototype models

The purpose of this study was to investigate if standard analysis of the vibrational characteristics of trabecular architectures can be used to detect changes in the mechanical properties due to progressive bone loss. A cored trabecular specimen from a human lumbar vertebra was microCT scanned and a three-dimensional, virtual model in stereolithography (STL) format was generated. Uniform bone loss was simulated using a surface erosion algorithm. Rapid prototype (RP) replicas were manufactured from these virtualised models with 0%, 16% and 42% bone loss. Vibrational behaviour of the RP replicas was evaluated by performing a dynamic compression test through a frequency range using an electro-dynamic shaker. The acceleration and dynamic force responses were recorded and fast Fourier transform (FFT) analyses were performed to determine the response spectrum. Standard resonant frequency analysis and damping factor calculations were performed. The RP replicas were subsequently tested in compression beyond failure to determine their strength and modulus. It was found that the reductions in resonant frequency with increasing bone loss corresponded well with reductions in apparent stiffness and strength. This suggests that structural dynamics has the potential to be an alternative diagnostic technique for osteoporosis, although significant challenges must be overcome to determine the effect of the skin/soft tissue interface, the cortex and variabilities associated with in vivo testing.     

硫酸钙骨水泥增强椎弓根螺钉置入骨质疏松椎体的瞬时稳定性

背景：由于内固定在骨质疏松骨上锚着力较差影响了其稳定性,因此需要新的固定方法,使用骨水泥或骨替代物增强内固定技术可以较好地解决这个问题。 目的：评价硫酸钙骨水泥增强的椎弓根螺钉置入骨质疏松椎体后的瞬时稳定性。 方法：选取新鲜小牛脊柱椎体,测量骨密度后,随机分为4组：①正常椎体椎弓根螺钉内固定组。②正常椎体椎弓根螺钉+硫酸钙骨水泥增强内固定组。③骨质疏松椎体椎弓根螺钉内固定组。④骨质疏松椎体椎弓根螺钉+硫酸钙骨水泥增强内固定组。将相同规格的椎弓根螺钉拧入测试椎体的椎弓根,测试其即刻最大轴向拔出力和最大破坏功耗,以评价硫酸钙骨水泥增强椎弓根螺钉的瞬时稳定性。 结果与结论：骨质疏松椎体较正常椎体的螺钉最大拔出力、最大破坏功耗明显减少(P < 0.05),而二者分别以骨水泥增强后的螺钉最大拔出力、最大破坏功耗明显增加(P < 0.05);正常组和骨质疏松组以骨水泥增强后螺钉的最大拔出力、最大破坏功耗相当。提示硫酸钙骨水泥增强后可以增加内固定螺钉的瞬时稳定性,硫酸钙骨水泥可以应用于骨质疏松患者骨折内固定的增强,具有较好的临床应用前景。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程全文链接：     

不同角度载荷下股骨头骨小梁的生物力学特性

目的 探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法 利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登（Garden）对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数（BV/TV）、骨表面积/骨体积（BS/BV）、骨小梁平均厚度（Tb.Th）、骨小梁数量（Tb.N）、骨小梁间距（Tb.Sp）等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果 加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。     

Calibration of the mechanical properties in a finite element model of a lumbar vertebra under dynamic compression up to failure

Finite element models (FEM) dedicated to vertebral fracture simulations rarely take into account the rate dependency of the bone material properties due to limited available data. This study aims to calibrate the mechanical properties of a vertebral body FEM using an inverse method based on experiments performed at slow and fast dynamic loading conditions. A detailed FEM of a human lumbar vertebral body (23,394 elements) was developed and tested under compression at 2,500 and 10 mm s⁻¹. A central composite design was used to adjust the mechanical properties (Young modulus, yield stress, and yield strain) while optimizing four criteria (ultimate strain and stress of cortical and trabecular bone) until the failure load and energy at failure reached experimental results from the literature. At 2,500 mm s⁻¹, results from the calibrated simulation were in good agreement with the average experimental data (1.5% difference for the failure load and 0.1% for the energy). At 10 mm s⁻¹, they were in good agreement with the average experimental failure load (0.6% difference), and within one standard deviation of the reported range of energy to failure. The proposed method provides a relevant mean to identify the mechanical properties of the vertebral body in dynamic loadings.     

不同角度载荷下股骨头骨小梁的生物力学特性

目的探讨不同角度载荷对股骨头骨小梁形态学与力学性能的影响,为研究股骨头坏死、塌陷的生物力学机制提供理论依据。方法利用12月龄羊股骨头和人尸体股骨头分别制作羊股骨头骨小梁试件94个和人股骨头骨小梁试件43个。按照受力方向与骨小梁主压力方向之间的不同夹角,将骨小梁以10°间隔分为内翻10°、0°和外翻10°、20°、30°共计5组,模拟股骨颈骨折内固定术后不同戈登(Garden)对线指数下的复位情况。通过分别对羊股骨头骨小梁进行micro-CT扫描、计算与压缩破坏试验以及对人尸体股骨头骨小梁进行循环压缩试验,分析不同受力方向下股骨头骨小梁的骨体积分数(BV/TV)、骨表面积/骨体积(BS/BV)、骨小梁平均厚度(Tb.Th)、骨小梁数量(Tb.N)、骨小梁间距(Tb.Sp)等形态学指标以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数等力学指标。结果加载方向与骨小梁的主压力方向之间夹角为0°时,BV/TV、Tb.Th以及弹性模量、极限强度、屈服强度、初始弹性模量、循环次数均为最大,而BS/BV与Tb.N为最小,并随着夹角增大前者呈递减而后者呈递增趋势。结论 12月龄羊股骨头骨小梁BV/TV与极限强度随受力方向与骨小梁主压力方向之间夹角变化的趋势与人股骨头骨小梁一致;加载方向与主压力骨小梁之间夹角增大时,股骨头骨小梁形态学与力学性能均下降;Garden指数偏离160°越大时,股骨头内骨小梁越易发生损伤。