Edwards装置中套棒位置对Harrington分离棒应力分布影响的研究

Edwards套棒装置可显著提高胸腰椎骨折复位率,但套棒的不同位置对Harrington棒的应力分布有明显影响。利用光弹性实验技术在实验载荷下可直观地观测到Harrington棒模型各部的应力情况。当套棒位于Harrington棒的齿棘区,光滑区交界处时,齿棘区应力集中最为严重,平均应力值分别高于套棒在Harrington棒工作长度内中点及远端1/4点时的23.9％,32.9％(棒前侧点)及31.3％、43.6％(棒后侧点)(P<0.01)。无论套棒位置如何。Harrington棒前侧点的应力值均高于棒后侧相应点(P<0.01)。实验结果提示使用Edwards装置时应尽量使套棒远离齿棘区,或选用齿棘区短的Harrington棒以减少应力集中造成的Harrington棒疲劳断裂。     

垂直载荷对哈氏棒中应力影响的光弹性分析

本文用二维光弹性方法研究了垂直载荷对哈氏棒应力分布的影响。发现在垂直载荷作用下棒的棘齿区呈现高应力集中，棘齿区应力高于光滑区，棘齿区应力值受垂直载荷影响最大，棒的前侧各点应力与垂直载荷呈线性相关。当增加水平载荷作用后，哈氏棒应力分布发生变化。     

两种改良型Harrington棒的应力分析

作者对Ｈａｒｒｉｎｇｔｏｎ棒加Ｅｄｗａｒｄｓ套棒（ＨＲＳ）和Ｃ型Ｈａｒｒｉｎｇｔｏｎ棒（ＨＲＣ）两种改良型Ｈａｒｒｉｎｇｔｏｎ棒进行应力分析，确定出棒体的危险截面和危险点，通过理论分析和光弹模型试验表明：在受伤脊柱复位程度相同的条件下，ＨＲＣ棒在棘齿根部的应力明显低于ＨＲＳ棒。从而提示临床，采用ＨＲＣ棒治疗脊柱压缩性骨折，在获得与ＨＲＳ棒相同的复位效果时，可减少Ｈａｒｒｉｎｇｔｏｎ棒从棘齿根部断棒     

Edwards套棒方法治疗胸腰段脊柱不稳定损伤的生物力学实验研究

本文报告Edwards套棒装置及单纯Harrington分离棒治疗胸腰椎不稳定损伤的力学实验研究结果。取成年猪新鲜胸腰椎脊柱6具,切断前纵韧带、椎间盘纤维环、后纵韧带,造成前中柱不稳定损伤15处。测力传感器固定于椎体前缘并骑跨损伤处,使之检测纵向复位力。单侧内固定装置固定。实验结果表明:单侧Edwards套棒装置产生纵向复位力量89N,较Harrington分离棒48.7N提高82.7％(P<0.0005);二种内固定装置分别用于胸、腰椎时,纵向复位力均无显著差异(P<0.05),表明胸段肋骨对纵向复位力无影响。生物力学分析,纵向复位力与横向前推力成正比例关系,增大内固定装置对伤椎的横向前推力,可提高纵向复位力量。同时其它学者也报告Edwards套棒装置具有良好的脊柱三维稳定作用。所以,作者认为Edwards套棒装置集对脊柱骨折复位与稳定于一体,是理想的内固定装置。     

枢椎齿突骨折的有限元分析

目的：建立枢椎的三维有限元(FE)模型，探讨在前、后方不同载荷下齿突的不同损伤机制和骨折类型。方法：对一例新鲜枢椎标本进行CT扫描，层厚1mm，扫描图像转换后输入微机，通过软件PRO／E重建枢椎的三维立体模型，再转入有限元软件MARK并赋予此模型物理材料属性，然后模拟齿突骨折的受力条件，在齿突中性矢状面对齿突施加不同角度的载荷，分析各种条件下枢椎模型的应力、应变分布，探讨相应条件下可能导致的枢椎齿突骨折类型。结果：(1)对于齿突前部斜向后下方载荷，应力集中区从齿突前上部斜贯穿至后下部；对于齿突前部斜向后上方载荷，应力集中区从齿突前下部斜贯穿至后上部；齿突腰部始终保持高应力；(2)在齿突后部载荷下，其应力集中情况与前部载荷相似，不过应力集中区位置有所偏下。结论：(1)在齿突中性矢状面，齿突前部载荷容易导致齿突腰部发生断裂，形成枢椎齿突Ⅱ型骨折，也可能导致基底部发生断裂，形成枢椎齿突Ⅲ型骨折；(2)齿突后部载荷更容易导致基底部发生断裂，形成枢椎齿突Ⅲ型骨折。     

三维有限元法分析钽棒置入治疗个体化股骨头坏死的力学效能北大核心

背景:研究报道股骨头前外侧柱对保髋的疗效起到关键性的作用,而中日友好医院分型(CJFH分型)强调前外侧柱的重要性,目前此分型中L型钽棒置入治疗的三维有限元研究不多。目的:以钽棒置入术为例,建立正常、坏死和L型坏死区前外侧柱钽棒置入的髋关节仿真的三维有限元模型,并进行有限元分析及力学效能对比,探讨前外侧柱的完整性对保髋疗效的重要性,为CJFH分型的治疗提供生物力学依据。方法:股骨头坏死的CJFH分型中L1、L2、L3型的坏死髋关节三维模型和正常髋关节三维模型选用团队已经做好的模型。在此基础上建立钽棒置入坏死股骨头的三维有限元模型,进行有限元分析。观察正常股骨头、坏死股骨头和钽棒置入坏死股骨头皮质骨壳应力分布及最大Mises应力值,对比并进行统计分析。结果与结论:(1)L型坏死股骨头负重区皮质骨壳的最大Mises应力均较正常股骨头升高,其中L1型升高21.76%,L2型升高31.02%,L3型升高42.79%;(2)钽棒置入术后股骨头负重区皮质骨壳的最大Mises应力较术前下降,其中L1型下降13.38%,L2型下降8.81%,L3型下降11.45%;(3)表明当股骨头发生坏死时,因坏死骨承载应力下降,导致股骨头皮质骨壳应力集中,所以坏死较正常的最大应力大,而分型程度越高,皮质骨壳所要承载的应力集中就越大;钽棒置入后承载了一部分应力,分型程度越低,纠正越明显;(4)结果表明,钽棒置入术纠正了坏死股骨头皮质骨壳部分应力,钽棒在一定程度范围内可以进行塌陷预防及起到支撑软骨下骨的生物力学作用;坏死股骨头外侧柱的完整性影响保髋疗效,可能外侧柱的存留越多,保髋疗效越好,而CJFH分型程度越高,塌陷风险越高,保髋疗效也越差。     

Luque棒生理负荷下的实验应力分析

Luque棒断裂、旋转和错动导致治疗失败,已引起临床专家的重视,目前尚缺乏有关的生物力学实验和分析。本实验应用8具新鲜猪脊柱,分4级载荷(100N,200N,300N,400N)测试Luque棒的应力分布及其影响因素。结果表明:生理负荷下,Luque棒中段承力最大,应力随负荷增加而增大,在400N负荷下,应力接近316L不锈钢材料的疲劳限度。钢丝固定的松紧度影响Luque棒受力的均衡。根据研究结果,作者找出了Luque棒生理轴压下的应力分布及其影响因素。作者同时还指出:新型脊柱内固定结构的研究,应考虑固定结构受力后的应力分布情况,依据力学原理,使固定物应力分布均衡。同时,强调Luque系统的规范化操作是保障脊柱固定可靠和固定物力学稳定的重要环节。     

聚醚醚酮棒与钛棒在后路腰椎椎间融合中的有限元分析北大核心

背景:聚醚醚酮棒是一种新型的半刚性固定材料,但是其在后路腰椎椎间融合术中的生物力学性能仍不清楚。目的:对比聚醚醚酮棒与钛棒在后路腰椎椎间融合过程中的生物力学性能,尝试回答聚醚醚酮棒是否有潜力成为钛棒的替代品,尤其在前柱支撑不充分的情况下。方法:利用有限元方法构建完整的人腰椎(L)模型,并进一步构建4个后路腰椎椎间融合模型:①聚醚醚酮棒+cage;②钛棒+cage;③聚醚醚酮棒+纯植骨;④钛棒+纯植骨。比较不同模型中节段活动度、相关结构应力以及应变。结果与结论:①所有手术模型在限制L节段活动度方面无明显差异;②与钛棒相比,聚醚醚酮棒增加了椎间植骨的平均应变、增加了终板以及cage的峰值应力,同时降低了螺钉以及骨-螺钉界面的峰值应力;聚醚醚酮棒的峰值应力与屈服应力之比为6%-26%,高于钛棒的3%-12%;③在L节段上,聚醚醚酮棒仅轻微地降低了节段活动度与椎间盘峰值应力;④因此与钛棒相比,聚醚醚酮棒可能降低假关节、螺钉断裂与松动的风险,但是也可能导致终板塌陷、cage损坏以及棒断裂的风险更高;聚醚醚酮棒在延缓邻近节段退变中可能较钛棒有微弱的优势;在不使用cage而仅采用骨移植物进行椎间融合时,聚醚醚酮棒也许是一个可供选择的方案。     

腓骨重建及小钛板固定下颌骨体部缺损的三维有限元分析

背景：临床研究中进行腓骨重建修复下颌骨缺损的力学研究是不现实的,而有限元分析法为下颌骨缺损修复重建的生物力学研究提供了新的方法。目的：建立腓骨重建小钛板固定下颌骨体部缺损的三维有限元模型,对其进行生物力学分析。方法：建立下颌骨体部缺损腓骨重建三维模型及内固定模型,在前牙、健侧第一磨牙、健侧第二磨牙加载    100 N咬合力,观察下颌骨模型重建前后的最大应力值和最大位移值情况,前牙加载和后牙加载下重建模型钛板、钛钉孔周围骨质的应力情况,前牙加载和后牙加载下腓骨前后端的最大位移值情况。结果与结论：正常下颌骨的最大应力集中在髁突颈部。在重建模型中,最大应力集中在健侧髁突颈部,加载相同咬合力的情况下重建下颌骨的最大应力值均大于正常下颌骨的最大应力值,前牙加载最大应力值大于后牙加载。在每块钛板内侧的两钉孔之间应力值最大,下颌角部位的应力比较集中,加载侧近下颌骨缺损处前上方的第一颗钛钉为下颌骨残端钛钉的最大应力集中部位,近腓骨中段后下方钛钉为腓骨端钛钉的最大应力集中部位。下颌骨残端近缺损处以及腓骨中段上板处的钉孔周围皮质骨为最大应力集中部位,前牙加载时的最大应力大于后牙加载时的最大应力。腓骨在X轴上从上缘到下缘的位移值不断减少,在Y轴上从前下方及后端至中份的位移值逐渐减少,在Z轴上从前端到后端的位移值逐渐减少。腓骨前端的最大位移值在Z轴方向,后端的最大位移值在Y轴方向上,前牙加载时的最大位移值均较后牙加载时的最大位移值大。说明下颌角后上方钛板最易折断,应对其进行加固处理;钛钉尖端和颈部应力比较大,应选择双皮质钛钉;腓骨端和下颌骨残端钛钉和钛板的应力比较大,应重视其稳定性和固位性;前牙咬合时的应力大于后牙咬合时的应力,修复后应避免前牙咬合。 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     

唇侧植骨不同种植修复体的三维有限元分析

目的分析植骨和修复体对种植修复体内部结构及周围骨组织应力分布的影响。方法建立由两种唇侧骨质牙槽骨模型支持且分别为钴铬合金烤瓷冠与二氧化锆全瓷冠修复的上颌中切牙种植修复体模型,对其进行力学加载,分析植骨与修复体对植体内部各结构与植体-骨界面应力分布的影响。结果植骨组中固位螺丝唇侧体部处及种植体唇侧骨组织中应力远低于非植骨组,但植骨组种植体颈部处的应力则高于非植骨组。相同骨质条件下,二氧化锆全瓷冠组在固位螺丝唇侧体部处的应力大于钴铬合金烤瓷冠组。结论修复体对种植修复体内部结构及周围骨组织应力分布的影响不大,但植骨影响的唇侧骨质差异可影响固位螺丝体部及植体-骨界面处的应力集中状况。     

Role of corrosion in Harrington and Luque rods failure

Ten in-vivo failed spinal instrumentation systems, i.e. six Harrington distraction rods with sublaminar hooks, one Harrington distraction rod with segmental wiring and three Luque rods with sublaminar wires, were fractographically analysed. In both Harrington and Luque rods corrosion fatigue was the predominant mechanism resulting in the failure. Five Harrington rods fractured at the first ratchet junction; fractures of the Luque rods were initiated by fretting of sublaminar wire with the rod surface in the presence of spinal non-union. Fretting and crevice corrosion were found to play an important role in compromising the segmental spinal instrumentation. The susceptibility of the 316 L CW austenitic stainless steel to pitting and relative resistance to crevice corrosion were measured by cyclic anodic polarization tests. The oxide inclusions have been found to play a significant role in the pitting of the alloy.     

Report on new types of intramedullary rods and treatment effectiveness data for selection of intramedullary rodding in osteogenesis imperfecta

Major advances in the surgical treatment of fractures of long bones in children with Osteogenesis Imperfecta (O.I.) have been made in the last several years. The current mainstay of treatment is bracing and active rehabilitation. When this fails surgery is indicated. The type of fixation device used is generally some type of stainless steel rod. The rod stabilizes the fracture as well as accepts the load across the fracture site thus enabling the fracture to heal. However, the current rods in use have complications. One such complication is cortical atrophy felt to be secondary to the removal of stress from the bone. This phenomena is called stress shielding. Stress shielding in the current rods prompted the study of two new types of rods which more closely approximate the modulus of elasticity of bone. The use of such rods should eliminate the problems of stress shielding. The following paper describes the effectiveness of the various intramedullary rods in the treatment of Osteogenesis Imperfecta fractures. It also reports on the initial results of two new types of intramedullary rods which more closely approximate the modulus of elasticity of bone and therefore may eliminate stress shielding. These rods may replace the stainless steel rods as the "gold standard" of therapy for surgical fixation of long bone fractures in children with Osteogenesis Imperfecta.     

Oscillations in rod and horizontal cell membrane potential: evidence for feed-back to rods in the vertebrate retina.

1. Rods and horizontal cells were studied with intracellular recordings in the retina of the toad, Bufo marinus; 161 cells were from the eyecup preparation and thirty were from the isolated perfused retina. 2. Of these cells, 39% exhibited either transient or sustained oscillations of membrane potential. Light flashes either evoked transient oscillations or temporarily abolished sustained oscillations. The amplitudes of the oscillations could be as large as 27 mV. The frequency of the oscillations at 25 degrees C was between 1-5 and 3-5 Hz and was strongly dependent on temperature and background illumination. 3. The rod oscillation amplitude and the peak of the horizontal cell light response increased similarly with increasing test flash diameters. They continued to grow for diameters much larger than those which increased the peak of the rod light response. 4. Perfusion of the isolated retina with 2 mM aspartate had only a small effect on the rod light response but it completely eliminated the horizontal cell light response as well as the oscillations recorded in both rods and horizontal cells. 5. It is believed that the oscillations result from a reverberating interaction between rods and neurones post-synaptic to rods. Thus, rods can be both post- as well as presynaptic retinal elements.     

Responses of single rods in the retina of the turtle

1. The responses of rods in the retina of the turtle, Chelydra serpentina, have been studied by intracellular recording.2. The identification of rods as the origin of the recorded responses has been confirmed by marking with Procion Yellow.3. The response to a small spot of light was a hyperpolarization which increased with increasing light intensity. For dim, small diameter stimuli, the shape of the rod response was similar to that of cones but 2x slower and 2x larger in amplitude. The time integral of the rod response to a dim, small diameter flash is, therefore, approximately 4x greater than the integral of the cone response.4. The shape of the rod response depended on the pattern of retinal illumination as well as stimulus intensity. Enlarging the area of illumination increased the peak amplitude and delayed repolarization following a light step. The area of retina which influenced the response was approximately 200 mum in radius.5. It is concluded that for dim light the responses of rods are larger than those of cones because of (i) a greater response to direct illumination and (ii) an enhancement of response by interaction from a large retinal area.     

Fracture modes under uniaxial compression in hydroxyapatite scaffolds fabricated by robocasting

The fracture modes of hydroxyapatite (HA) scaffolds fabricated by direct-write assembly (robocasting) are analyzed in this work. Concentrated HA inks with suitable viscoelastic properties were developed to enable the fabrication of prototype structures consisting of a 3-D square mesh of interpenetrating rods. The fracture behavior of these model scaffolds under compressive stresses is determined from in situ uniaxial tests performed in two different directions: perpendicular to the rods and along one of the rod directions. The results are analyzed in terms of the stress field calculated by finite element modeling (FEM). This analysis provides valuable insight into the mechanical behavior of scaffolds for bone tissue engineering applications fabricated by robocasting.     

A new method for continuous intraoperative measurement of Harrington rod loading patterns

A new method has been developed for continuous intra-operative monitoring of bone and implant loading patterns in the operative correction of scoliosis using the Harrington distraction rod. The method incorporates a strain gauge instrumented, distal Harrington hook and similarly equipped Harrington operating instruments (outrigger and distractor). These latter instruments are used to calibrate the hook's response to bone loads under existing operative conditions. Alternative methods of monitoring loading patterns were explored and rejected because they were noncontinuous, more difficult to use, altered the mechanics of the system, or required more expensive components. The method established is being used to avoid bone rupture or rod damage while gaining maximum spinal correction and to determine the effect of auxiliary implant components on loading patterns.