低弹性模量外固定系统对股骨干骨折模型的生物力学研究

目的 通过在模拟股骨上对不同弹性模量的外固定系统进行生物力学测试,探讨不同弹性模量外固定系统对股骨干骨折应力及其分布的影响.方法 选择8套与人体股骨力学性质类似的玻璃钢制成股骨干骨折模型,在模型上分别安装Ti-24Nb-4Zr-7.9Sn(低弹性模量组,弹性模量为33 Gpa,4套)和Ti-6Al-4V(高弹性模量组,弹性模量为110 Gpa,4套)钛合金半针,连接套夹和碳纤维外固定棒,在骨折断面,外固定半针以及钉道周围粘贴电阻应变计,分析局部应力,测量不同弹性模量外固定系统在同样载倚条件下骨折断面及钉道周围应力的大小和分布.结果 在实验载倚条件下,随着载荷和力矩的增大,高弹性模量组与低弹性模量组骨折断端和钉道周围应力有不同程度增大.当侧压载荷为90 N时,两组的侧压应变值分别为(6.5±3.5)×10~(-6)、(43.5±22.7)×10~(-6);当侧压载荷为300 N时,应变值为(16.5±0.7)×10~(-6)、(140.5±9.5)×10~(-6).当弯曲载荷为1.6 N·m时,两组的应变值分别为(0.3±0.5)×10~(-6)、(47.1±31.5)×10~(-6);当弯曲载荷为11.0 N·m时,应变值分别为(359.7±39.9)×10~(-6)、(453.5±29.0)×10~(-6).当侧压载荷≥90 N或弯曲载倚介于1.6～8.8 N·m时,两组之间骨折断端应力应变值差异有统计学意义(P<0.05).在3种力学作用下,与高弹性模量组相比,低弹性模量组钉道局部应力分布更均匀,应力相对集中的针道局部应力变小.结论 低弹性模量外固定系统有利于应力传导,更符合生物力学的要求,从而可能有效避免应力遮挡效应,促进骨折愈合.     

异体骨接骨板联合不同螺钉治疗股骨干骨折有限元分析

目的对比分析异体骨接骨板分别联合可吸收螺钉(聚-DL-乳酸)和钛合金螺钉(Ti-6Al-4V)治疗股骨干骨折的应力分布情况,验证可吸收螺钉的强度,为临床提供力学依据。方法利用螺旋CT扫描股骨,将扫描数据以DICOM格式导入mimics软件中,建立股骨三维模型。在proe5.0中建立接骨板模型和螺钉模型(简化为圆柱),装配完成后,导入ansys12.0划分网格、材料赋值,并施加700 N轴向载荷、15 N·m弯曲载荷、15 N·m扭转载荷。结果在三种载荷下6根可吸收螺钉最大主应力的最大值为5.75 Mpa、6根钛合金螺钉最大主应力的最大值为24.9 Mpa;两种不同螺钉固定下,股骨和接骨板的应力分布基本相同。结论可吸收螺钉适应于同种异体骨接骨板的固定,与钛合金螺钉相比,具有减少骨头螺钉孔处的应力遮挡的优点。     

基于有限单元法的股骨干粉碎性骨折锁定板内固定优化仿真

目的研究粉碎性股骨干骨折采用锁定板内固定时选择不同螺钉位置固定情况下锁定板及螺钉最大应力情况。方法通过64层螺旋CT扫描采集27名健康志愿者左侧股骨数据并导入Mimics软件,建立骨骼3D模型并依据CT值为股骨赋材料属性。用三坐标测量仪扫描锁定板,并将生成的点云文件导入Geomagic Studio生成光顺曲面及实体文件;将股骨及锁定板文件导入有限元分析软件Abaqus进行装配,施加压力和扭矩载荷,并对锁定板及螺钉的应力分布进行求解。结果对于粉碎性股骨干骨折,在压力和力矩载荷作用下,不同螺钉位置组合时的锁定板及螺钉上应力峰值均出现在最内侧螺钉处,即最靠近骨折线处;并且随着最内侧固定螺钉外移,锁定板及螺钉上分布的应力峰值均逐渐增大。结论对于粉碎性股骨干骨折锁定板内固定,使用较多的螺钉固定可使螺钉及锁定板上的应力峰值减小,同时最内侧螺钉尽量靠近骨折端。     

新型低弹高强度钛合金髓内钉对大鼠骨折愈合的影响

目的观察新型低弹性模量高强度钛合金髓内钉对大鼠骨折愈合的作用及应力遮挡效应。方法以SD大鼠为研究对象,采用Utvag方法制备双股骨骨折模型,选用弹性模量分别为110 GPa和33 GPa的钛合金制成髓内针固定骨折,左侧为高弹组,右侧为低弹组,分别于术后4、12周行Micro-CT和生物力学测定,检测骨小梁的体积(BV)、样本体积(TV)、骨体积分数(BVF)及最大载荷等指标,比较骨折区域骨痂形成、全股骨骨量及力学性能的变化,并进行统计学分析。结果术后4周,RIO1区低弹组TV高于高弹组、BVF低于高弹组,BV与高弹组无明显差异;RIO2区各值无明显差异。术后12周,RIO1区和RIO2区,低弹组TV、BV、BVF和最大载荷均高于高弹组。结论新型低弹性模量钛合金内植物有利于骨折后早期新骨的形成,可减少固定节段骨量丢失,提高骨折愈合远期质量。     

股骨干骨折接骨板或髓内针固定的局部并发症

目的 探讨股骨干骨折局部并发症发生的影响因素,并比较接骨板和髓内针固定方法在并发症方面的差异。方法 对我院１９８５－１９９４年间３２５例经内固定治疗的股骨干骨折进行分析。结果 ７２例发生局部并发症,发生率为２２％,其中髓内针组４６例;接骨板组２６例。结论髓内针固定股骨干骨折较接骨板有明显的优势,但在股骨下段,粗隆下肌折应用接骨板是较好的选择。     

股骨生物力学特性的有限元分析

目的对股骨的生物力学特性进行研究以指导临床工作。方法根据股骨的螺旋CT片,采用计算机辅助技术建立股骨的三维有限元模型,通过分别对模型施加350、700、1400和2100N的垂直载荷及行走载荷,观察股骨的应力分布,并对结果做出分析。结果在各种载荷下,股骨颈和股骨干各有一个应力集中部位。股骨颈的应力集中部位在小转子上方、稍偏股骨颈后方处,应力值分别为6.3、12.6、25.1、37.7和20.8MPa;而股骨干以其内侧中下1/3交界处的应力最大,应力值分别为7.3、14.5、29.0、43.5和31.3MPa。结论股骨颈处的压力骨小梁和股骨距是主要的承重结构,内固定的放置应与压力骨小梁的方向一致,并紧贴股骨距;股骨干应力骨折好发于其中下1/3交界处,与此处应力集中有关。     

动力髋螺钉与股骨近端防旋髓内钉治疗骨质疏松性股骨转子间骨折的有限元比较研究

目的 建立骨质疏松性改良Evans分型Ⅲ型股骨转子间骨折的有限元模型,比较动力髋螺钉(DHS)和股骨近端防旋髓内钉(PFNA)内固定在不同表观骨密度和载荷下的生物力学特性. 方法 选择1例改良Evans分型为Ⅲ型的老年股骨转子间骨折患者,男性,年龄为75岁,身高172 cm,体质量为70 kg.对患者股骨中上2/3段进行CT扫描,建立骨折模型并予虚拟复位,分别在此模型上搭载DHS(模型Ⅰ组)和PFNA(模型Ⅱ组)两种内固定物.每组分别考虑7种表观骨密度(70％、80％、90％、100％、110％、120％、130％的表观骨密度)及3种载荷(0.5、1.0、3.0倍体质量)下的受力情况,共有42种工况.比较各种条件下两组固定模型的股骨Von Mises应力峰值、内固定物Von Mises应力峰值及股骨单元失效率. 结果 在同一载荷下,模型Ⅰ组股骨及内固定物所承受应力、股骨单元失效率均大于模型Ⅱ组,差异有统计学意义(P＜0.05);同一模型随着载荷的增加,股骨及内固定物所承受的应力、股骨单元失效率均上升,差异有统计学意义(P＜0.05).在3.0倍体质量载荷、70％表观骨密度下,模型Ⅰ组和模型Ⅱ组的股骨最大应力值分别为84.702、38.986 MPa,内固定物最大应力值分别为952.557、580.134 MPa,股骨单元失效率分别为3.25％、7.99×10-3％. 结论 对于骨质疏松性改良Evans分型Ⅲ型股骨转子间骨折,PFNA固定较DHS固定具有明显的生物力学优势,固定强度更好,且不易导致内固定失效.     

MIPPO技术下胫骨近端骨折LCP固定的三维有限元研究

目的 比较胫骨近端内侧LCP接骨板通过锁定孔和加压孔固定在不同载荷下的应力分布特点,探讨锁定固定和加压固定的优缺点.方法 建立胫骨近端骨折LCP接骨板锁定固定和加压固定的三维有限元模型,采用有限元分析法,分析模型在轴向加压、三点侧弯、扭转状态下的应力分布.结果 ①LCP接骨板在锁定固定和加压固定下,都在骨折处和骨折近端第一个锁定(加压)孔处有应力集中现象;②LCP接骨板锁定固定应力均值大于加压固定.结论 锁定固定和加压固定都使钢板在骨折处和接骨板第一个锁定(加压)孔处容易发生断裂,加压固定比锁定固定更稳固,但锁定固定更符合BO理论要求.     

股骨干骨折锁定板内固定治疗的有限元分析

目的研究股骨干骨折采用锁定板内固定,选择不同螺钉位置情况下,锁定板及螺钉最大应力情况。方法通过采集23位健康志愿者左股骨CT数据及12孔锁定板外形数据进行有限元分析前处理,并导入有限元分析软件进行装配和求解。结果不同固定方式下的锁定板及螺钉上最大应力值均出现在最内侧螺钉处,即最靠近骨折线处。对于简单骨折,随着最内侧固定螺钉的外移,锁定板及螺钉上分布的最大应力均逐渐减小;对于粉碎性骨折,则随着最内侧固定螺钉的外移,锁定板及螺钉上分布的最大应力均逐渐增大。结论对于股骨干骨折锁定板内固定,若为简单骨折,应在保证固定强度的前提下使最内侧螺钉尽量远离骨折端;若为粉碎性骨折,则应在保证固定强度的前提下使最内侧螺钉尽量靠近骨折端。     

利用有限元探究内固定治疗股骨颈骨折的生物力学研究

目的:利用有限元分析研究不同内固定治疗Pauwels Ⅲ型股骨颈骨折的生物力学特点。方法:选取1名健康受试者的股骨CT数据进行三维重建,骨折造模,装配动力髋螺钉、锁定加压钢板、三枚空心钉、四枚空心钉和髓内钉,建立有限元模型,在股骨头顶端轴向加载1400 N应力。研究不同内固定的应力分布和位移分布、股骨的应力分布和位移分布,并比较内固定和股骨模型的应力峰值和位移峰值。结果:股骨和内固定应力较大区域均分布于股骨颈及股骨干部位,且在骨折线附近均出现应力增大的现象;内固定位移分布主要集中于股骨头内螺钉尖端位置,股骨位移集中于股骨头顶端,应力加载位置。四枚空心钉的应力最小,峰值为135.3 MPa;锁定加压钢板的应力最大,峰值为405.9 MPa,但锁定加压钢板的位移12.3 mm为最小峰值;三枚空心钉的位移18.8 mm为最大峰值;三枚空心钉固定时,股骨受力最小,应力峰值为36.8 MPa,但股骨位移最大,峰值为19.3 mm;锁定加压钢板固定时,股骨受力104.6 MPa为最大应力峰值而位移12.6mm为最小位移峰值。结论:锁定加压钢板在固定股骨颈骨折时稳定性最高,但股骨和内固定承受更大的压力和剪切力;动力髋螺钉固定短期内促进骨折愈合较有优势,但长期固定时髓内钉固定更佳。     

The effects of nail rigidity on fracture healing in rats with osteoporosis

Background and purpose Stress shielding from rigid internal fixation may lead to refracture after removal of the osteosynthesis material. We investigated the effect of a low-rigidity (Ti-24Nb-4Zr-7.9Sn) intramedullary nail regarding stress shielding and bone healing of osteoporotic fractures in the rat.Methods 40 female Sprague-Dawley rats, aged 3 months, were divided into the following groups: sham-operation (SHAM) (n = 10), ovariectomized (OVX) (n = 10) and OVX-fracture (n = 20). 10 SHAM rats and 10 OVX rats were killed after 12 weeks to provide biomechanical data. Ovariectomy was performed 12 weeks before fracturing both femurs in 20 rats. The left fracture was stabilized with a high-rigidity titanium alloy pin (Ti-6Al-4V; elastic modulus 110 GPa) and the right with a low-rigidity (Ti-24Nb-4Zr-7.9Sn; elastic modulus 33 GPa). The bony calluses were examined by micro-CT at 6 and 12 weeks after fracture, bone volume (BV) and total volume (TV) were determined at the callus region (ROI1) and the total femur (ROI2). Subsequently, the bones were tested mechanically by a three-point bending test.Results In the low-rigidity group, TV (ROI1) increased at 6 weeks, but BV (ROI1), BV (ROI2) were similar but maximum load increased. At 12 weeks, the maximum load and also BV (ROI1, ROI2) were increased in the low-rigidity group.Interpretation The low-rigidity nail manufactured from Ti-24Nb-4Zr-7.9Sn showed better external callus formation, seemed to reduce effects of stress shielding, and reduced bone resorption better than the stiffer nail. The low-rigidity nail was strong enough to maintain alignment of the fracture in the osteoporotic rat model without delayed union.     

Bisphosphonate (pamidronate/APD) prevents arthritis-induced loss of fracture toughness in the rabbit femoral diaphysis

Patients with rheumatoid and other inflammatory arthritis have an increased risk for fracture. This study was designed to determine the effect of experimental inflammatory arthritis on the material properties (fracture toughness and shear modulus) and structural properties (torque, angular defelection, and absorbed energy) of femoral diaphyseal bone tested in torsion to fracture, as well as the effect on these properties of APD (3-amino-1-hydroxypropylidene-1,1-bisphosphonate), a drug known to block osteoclast activity. Two dose levels were investigated. Experimental inflammatory arthritis was induced by intra-articular injection of carrageenan into the right tibiofemoral joint, given over 7 weeks, in three groups of animals. Simulataneously, daily subcutaneous injections of APD were given to three groups of rabbits. Five groups (12 animals each) were established: normal, arthritis, normal/high dose APD, arthritis/high dose APD, and arthritis/low dose APD. The diaphyses of each excised right femur were loaded to fracture in torsion at an angular deflection rate of 8°/sec. In the arthritis group, the fracture toughness was 39% lower than in the normal group, and the structural properties all were reduced significantly. By contrast, the shear modulus was unaffected by arthritis. In this study, the higher dose level (0.3 mg/kg of body weight) of APD prevented loss of fracture toughness and maintained the structural properties in experimental inflammatory arthritis; the low dose was not effective.     

Elastic modulus of calcified cartilage is an order of magnitude less than that of subchondral bone

The elastic moduli of calcified cartilage and subchondral bone tissues were measured experimentally with use of a three-point bending test. Specimens were obtained from a bovine patella and the distal end of a bovine femur, from two different animals. Fifteen specimens were tested as “pure” subchondral bone beams, and 15 were tested as composite calcified cartilage/subchondral bone beams. A least-squares optimization scheme was used to obtain modulus values from the composite beams. The elastic modulus for subchondral bone calculated from the “pure” subchondral bone beams was 2.3 ± 1.5 GPa (3.9 ± 1.5 GPa for specimens from the femur and 1.6 ± 0.7 GPa for specimens from the patella). The composite beam optimization resulted in a modulus for subchondral bone of 5.7 ± 1.9 GPa and a modulus for calcified cartilage of 0.32 ± 0.25 GPa. The modulus for the calcified cartilage was more than an order of magnitude lower than the modulus of the underlying subchondral bone. This supports the idea that the zone of calcified cartilage forms a transitional zone of intermediate stiffness between the articular cartilage and the subchondral bone.     

Stress fracture in military recruits: gender differences in muscle and bone susceptibility factors

A total of 693 female U.S. Marine Corps recruits were studied with anthropometry and dual-energy X-ray absorptiometry (DXA) scans of the midthigh and distal third of the lower leg prior to a 12 week physical training program. In this group, 37 incident stress fracture cases were radiologically confirmed. Female data were compared with male data from an earlier study of 626 Marine recruits extended with additional cases for a total of 38 stress fracture cases. Using DXA data, bone structural geometry and cortical dimensions were derived at scan locations and muscle cross-sectional area was computed at the midthigh. Measurements were compared within gender between pooled fracture cases and controls after excluding subjects diagnosed with shin splints. In both genders, fracture cases were less physically fit, and had smaller thigh muscles compared with controls. After correction for height and weight, section moduli (Z) and bone strength indices (Z/bone length) of the femur and tibia were significantly smaller in fracture cases of both genders, but patterns differed. Female cases had thinner cortices and lower areal bone mineral density (BMD), whereas male cases had externally narrower bones but similar cortical thicknesses and areal BMDs compared with controls. In both genders, differences in fitness, muscle, and bone parameters suggest poor skeletal adaptation in fracture cases due to inadequate physical conditioning prior to training. To determine whether bone and muscle strength parameters differed between genders, all data were pooled and adjusted for height and weight. In both the tibia and femur, men had significantly larger section moduli and bone strength indices than women, although women had higher tibia but lower femur areal BMDs. Female bones, on average, were narrower and had thinner cortices (not significant in the femur, p = 0.07). Unlike the bone geometry differences, thigh muscle cross-sectional areas were virtually identical to those of the men, suggesting that the muscles of the women were not relatively weaker.     

The effects of nail rigidity on fracture healing in rats with osteoporosis

Background and purpose Stress shielding from rigid internal fixation may lead to refracture after removal of the osteosynthesis material. We investigated the effect of a low-rigidity (Ti-24Nb-4Zr-7.9Sn) intramedullary nail regarding stress shielding and bone healing of osteoporotic fractures in the rat.

Methods 40 female Sprague-Dawley rats, aged 3 months, were divided into the following groups: sham-operation (SHAM) (n = 10), ovariectomized (OVX) (n = 10) and OVX-fracture (n = 20). 10 SHAM rats and 10 OVX rats were killed after 12 weeks to provide biomechanical data. Ovariectomy was performed 12 weeks before fracturing both femurs in 20 rats. The left fracture was stabilized with a high-rigidity titanium alloy pin (Ti-6Al-4V; elastic modulus 110 GPa) and the right with a low-rigidity (Ti-24Nb-4Zr-7.9Sn; elastic modulus 33 GPa). The bony calluses were examined by micro-CT at 6 and 12 weeks after fracture, bone volume (BV) and total volume (TV) were determined at the callus region (ROI1) and the total femur (ROI2). Subsequently, the bones were tested mechanically by a three-point bending test.

Results In the low-rigidity group, TV (ROI1) increased at 6 weeks, but BV (ROI1), BV (ROI2) were similar but maximum load increased. At 12 weeks, the maximum load and also BV (ROI1, ROI2) were increased in the low-rigidity group.

Interpretation The low-rigidity nail manufactured from Ti-24Nb-4Zr-7.9Sn showed better external callus formation, seemed to reduce effects of stress shielding, and reduced bone resorption better than the stiffer nail. The low-rigidity nail was strong enough to maintain alignment of the fracture in the osteoporotic rat model without delayed union.     

成骨活性肽对骨折愈合生物力学性能的影响

目的观察自行设计合成的具有成骨活性的小分子多肽对小鼠股骨骨折愈合生物力学性能的影响,评价其促进骨折愈合的能力。方法选择8周龄雌性C57BL/6J小鼠40只,随机分为对照组和多肽组两组,每组各20只。所有动物制备左侧股骨骨折模型,分组植入复合PBS或多肽的胶原材料。术后第3周行三点弯曲实验,观察各标本最大载荷、弹性载荷、最大挠度、弹性挠度、最大应力、弹性模量等生物力学指标的变化情况。结果多肽组各项生物力学指标均显著高于对照组(P<0.01)。结论合成的成骨活性多肽能明显增强小鼠股骨骨折愈合的生物力学性能。     

Biomechanical characterization of osseointegration: An experimental in vivo investigation in the beagle dog

This study reports the results of torsion tests, pull-out tests, and lateral Ioading tests on osseointegrated commercially pure titanium fixtures. The tests were performed in vivo on six beagie dogs. Three fixtures, each with a diameter of 3.7mm, were installed bilaterally in the tibia of each animal. The mean maximal pull-out load was 1.55 kN (n = 4) the mean maximal lateral transverse load was 0.21 kN (n = 2), the mean maximal lateral axial load was (0.18 kN (n = 2)) the mean breakpoint torque was 0.31 Nm (n = 3), and the mean maximal torque was 0.43 Nm (n = 3). The torsion test revealed an almost immediate plastic deformation of the interface between the implant and bone: this indicates that although the contact between the bone and the implant is close, there is no strong bond, at least not in shear. The major transfer of load from the implant to the surrounding bone tissue must therefore depend on the design of the implant. A histological evaluation with measurements of the amount of bone in contact with the fixtures was performed. By the use of the histological and mechanical data, it is possible to estimate shear stresses in bone tissue (pull-out test) and in the interface (torque test), The mean maximal shear stress in bone tissue in the pull-out tests was 100 MPa (n = 4); the mean shear stress in the interface was 4.3 MPa (n = 3) in the torsion tests at the breakpoint torque and was 6.0 MPa (n = 3) at the maximal torque. It was also possible to estimate the shear modulus of elasticity in the pull-out and torque tests. The mean shear modulus in pull-out was 119 MPa (n = 4), and the mean apparent shear modulus in torsion was 9 kPa (n = 3) for an assumed interface thickness of 100 nm and was 86 kPa (n = 3) for an assumed interface thickness of 1.000 nm.     

Cancellous bone mechanical properties from normals and patients with hip fractures differ on the structure level, not on the bone hard tissue level

Osteoporosis is currently defined in terms of low bone mass. However, the source of fragility leading to fracture has not been adequately described. In particular, the contributions of bone tissue properties and architecture to the risk or incidence of fracture are poorly understood. In an earlier experimental study, it was found that the architectural anisotropy of cancellous bone from the femoral heads of fracture patients was significantly increased compared with age- and density-matched control material (Ciarelli et al., J Bone Miner Res 15:32-40; 2000). Using a combination of compression testing and micro-finite element analysis on a subset of cancellous bone specimens from that study, we calculated the hard tissue mechanical properties and the apparent (macroscopic) mechanical properties. The tissue modulus was 10.0 GPa (SD 2.2) for the control group and 10.8 GPa (SD 3.3) for the fracture group (not significant). There were no differences in either the apparent yield strains, percentages of highly strained tissue, or the relationship between apparent yield stress and apparent elastic modulus. Hence, a difference in the tissue yield properties is unlikely. At the apparent level, the fracture group had a significantly decreased transverse stiffness, resulting in increased mechanical anisotropy. These changes suggest that bone in the fracture group was "overadapted" to the primary load axis, at the cost of fragility in the transverse direction. We conclude that individuals with a history of osteoporotic fractures do not have weaker bone tissue. Architectural and mechanical anisotropy alone renders their bone weaker in the nonprimary loading direction.