酒精灭活骨复合人工假体治疗股骨远端骨巨细胞瘤及有限元分析

目的 探讨酒精灭活骨复合人工假体治疗股骨远端骨巨细胞瘤的临床疗效.方法 2007年1月至2008年10月应用酒精灭活骨复合旋转铰链膝关节治疗股骨远端骨巨细胞瘤5例,男3例、女2例;年龄22～40岁,平均29.6岁.3例为术后复发病例,2例伴病理性骨折.均为CampanacciⅢ级.选择1名18岁成年男性健康志愿者,利用...     

Anatomy of the epicondyles of the distal femur: MRI analysis of normal knees

Knowledge of precise anatomic landmarks and relationships of the distal femur can be helpful in knee surgery, especially primary and revision total knee arthroplasty. We analyzed 104 consecutive routine knee magnetic resonance imaging studies to define useful landmarks and relationships. The epicondyles are described, and the relationship of the epicondyles to the joint line is defined in multiple planes. Some significant gender differences were noted. The distance from the epicondyles to the joint line correlates with the transepicondylar width of the distal femur. This information can be helpful in determining appropriate joint line position intraoperatively. The posterior condylar angle averaged 3.11 degrees for all patients, and a tendency for the posterior condylar angle to increase with age was noted, but further study of this tendency is needed.     

髓腔改变对股骨近端假体-骨界面应力的影响

目的 建立股骨近端假体-骨界面应力有限元分析模型.并对中国成年人股骨近端正常受力、翻修过程中扩髓条件下进行静态有限元分析.方法 运用逆向工程与有限元的理论.对CT图像采用了滤波、边界提取、二值化等方法进行处理,所得数据用CAD软件经过曲线重构、曲面重构、实体重构,加工出股骨应力模型.将不同载荷施加与假体-骨界面,改变股骨骨皮质的厚度、假体长度等参数,进行静态模拟应力分析.结果 建立起以国人股骨为基础的有效的假体-骨界面应力分布规律三维有限元模型.股骨的受力主要集中在小转子和大转子之间的股骨距分布区域,并且随着载荷的增加而递增;假体增粗至原来的120%时,股骨最大应力已经接近极限应力值.结论 构建的解剖型股骨假体-骨界面三维有限元模型,几何相似性好.模拟应力分析结果提示接受关节置换的患者应该尽量避免登山等接近加载量极限的活动;对于髓腔骨缺损严重的翻修患者提倡应用骨移植材料.谨慎采用增粗假体固定.     

Computational finite element bone mechanics accurately predicts mechanical competence in the human radius of an elderly population

High-resolution peripheral quantitative computed tomography (HR-pQCT) is clinically available today and provides a non-invasive measure of 3D bone geometry and micro-architecture with unprecedented detail. In combination with microarchitectural finite element (μFE) models it can be used to determine bone strength using a strain-based failure criterion. Yet, images from only a relatively small part of the radius are acquired and it is not known whether the region recommended for clinical measurements does predict forearm fracture load best. Furthermore, it is questionable whether the currently used failure criterion is optimal because of improvements in image resolution, changes in the clinically measured volume of interest, and because the failure criterion depends on the amount of bone present. Hence, we hypothesized that bone strength estimates would improve by measuring a region closer to the subchondral plate, and by defining a failure criterion that would be independent of the measured volume of interest. To answer our hypotheses, 20% of the distal forearm length from 100 cadaveric but intact human forearms was measured using HR-pQCT. μFE bone strength was analyzed for different subvolumes, as well as for the entire 20% of the distal radius length. Specifically, failure criteria were developed that provided accurate estimates of bone strength as assessed experimentally. It was shown that distal volumes were better in predicting bone strength than more proximal ones. Clinically speaking, this would argue to move the volume of interest for the HR-pQCT measurements even more distally than currently recommended by the manufacturer. Furthermore, new parameter settings using the strain-based failure criterion are presented providing better accuracy for bone strength estimates.     

Segmental amputation for recurrent malignant bone tumors of the distal femur

We describe an alternative method for lengthening a short femoral stump after wide amputation of a malignant bone tumor of the distal femur in two patients. The method consists of two procedures during the operation. The first procedure is amputation of the affected cylindrical segment of the involved limb. The second procedure is elongation of the amputation stump using the tumor-free segment of the ipsilateral lower leg as a free composite osseous myocutaneous graft. Both patients had good function and were satisfied with the results with no complications or tumor recurrence 4 years postoperatively. We think the segmental amputation is a good procedure that results in a longer functional stump in patients who have above-knee amputation.     

In vivo estimation of bone stiffness at the distal femur and proximal tibia using ultra-high-field 7-Tesla magnetic resonance imaging and micro-finite element analysis

The goal of this study was to demonstrate the feasibility of using 7-Tesla (7T) magnetic resonance imaging (MRI) and micro-finite element analysis (μFEA) to evaluate mechanical and structural properties of whole, cortical, and trabecular bone at the distal femur and proximal tibia in vivo. 14 healthy subjects were recruited (age 40.7 ± 15.7 years). The right knee was scanned on a 7T MRI scanner using a 28 channel-receive knee coil and a three-dimensional fast low-angle shot sequence (TR/TE 20 ms/5.02 ms, 0.234 mm × 0.234 mm × 1 mm, 80 axial images, 7 min 9 s). Bone was analyzed at the distal femoral metaphysis, femoral condyles, and tibial plateau. Whole, cortical, and trabecular bone stiffness was computed using μFEA. Bone volume fraction (BVF), bone areas, and cortical thickness were measured. Trabecular bone stiffness (933.7 ± 433.3 MPa) was greater than cortical bone stiffness (216 ± 152 MPa) at all three locations (P < 0.05). Across locations, there were no differences in bone stiffness (whole, cortical, or trabecular). Whole, cortical, and trabecular bone stiffness correlated with BVF (R ≥ 0.69, P < 0.05) and inversely correlated with corresponding whole, cortical, and trabecular areas (R ≤ −0.54, P < 0.05), but not with cortical thickness (R < −0.11, P > 0.05). Whole, cortical, and trabecular stiffness correlated with body mass index (R ≥ 0.62, P < 0.05). In conclusion, at the distal femur and proximal tibia, trabecular bone contributes 66–74% of whole bone stiffness. 7T MRI and μFEA may be used as a method to provide insight into how structural properties of cortical or trabecular bone affect bone mechanical competence in vivo.     

Gender differences in trabecular bone architecture of the distal radius assessed with magnetic resonance imaging and implications for mechanical competence

High-resolution magnetic resonance imaging (hrMRI) has recently made it possible to evaluate trabecular bone structure in vivo. Despite obvious gender differences in fracture incidence at the distal radius, little is known about gender differences in trabecular bone microarchitecture and its relationship to the structural strength of the forearm. The aim of this study was to determine trabecular bone structure in the distal radius of elderly women and men and its correlation with failure loads of the distal radius as determined in a fall configuration. Specifically, we tested the hypotheses that structural indices differ between women and men and that they offer information that is independent from BMD for predicting structural strength. Intact right arms were obtained from 73 formalin-fixed cadavers (age 80±11 years, 43 women, 30 men). Trabecular structural indices (apparent bone volume fraction [app. BV/TV], trabecular number [app. Tb.N], trabecular separation [app. Tb.Sp], trabecular thickness [app. Tb.Th] and fractal dimension [Frac.Dim]) were assessed in the distal metaphysis, using hrMRI with 156 µm in-plane resolution and proprietary digital image analysis, while BMD was measured with dual X-ray absorptiometry (DXA). Women displayed significantly lower BMD (–29.8%, p <0.001), app. BV/TV (–8.2%, p <0.05) and app. Tb.Th (–10.2%, p <0.001) than men, whereas app. Tb.N, app. Tb.Sp. and fractal dimension did not differ significantly. Structural parameters differed between normal and osteopenic women (BV/TV: –11%, p <0.01; Tb.Th: –8%, p <0.001) and between normal and osteoporotic women BV/TV: –21%, p <0.001; Tb.Th: –16%, p <0.001). App. BV/TV, app. Tb.Th and fractal dimension provided information independent from BMD in the prediction of radial failure loads in multiple regression models. These findings imply that it should be of clinical interest to monitor both bone mass and trabecular microstructure for predicting osteoporotic fracture risk.     

Increased bone strength is associated with improved bone microarchitecture in intact female rats treated with strontium ranelate: a finite element analysis study

Strontium ranelate has been previously shown to act on bone metabolism and to be effective in postmenopausal osteoporosis treatment by preventing vertebral and non-vertebral fractures. Animal studies explicitly demonstrated that bone strength was improved with strontium ranelate treatment, but the contribution of either improved bone microarchitecture or intrinsic quality of the bone tissue is not clear. Therefore, the purpose of this research was to address this issue by using the unique capability of finite element (FE) analysis to integrate both intrinsic bone quality properties from nano-indentation and microarchitecture measured by micro-computed tomography (μCT). The two groups included intact female Fischer rats fed a normal diet (controls, N=12) or a diet containing strontium ranelate (900mg/kg/day; N=12) for a period of 104weeks. The L(5) vertebra was scanned by μCT and a morphological analysis of the vertebral body was performed. Subsequently, those μCT data were the basis of FE models with added virtual endcaps that simulated axial compression tests. The FE models were solved with the vertebral bodies only and repeated with the vertebral processes intact. In the initial stages, the intrinsic bone properties were kept constant between the control and the treated animals in order to independently study the impact of microarchitectural changes on bone strength. Morphological data indicated a significant improvement in bone microarchitecture associated with strontium ranelate compared to controls, including a 40% (p<0.01) higher trabecular thickness, a 28% (p<0.01) higher cortical thickness, and no significant change in the number of trabeculae (p=0.56). The poor correlation of bone strontium content against bone volume fraction (BV/TV) (R(2)=0.013, p=0.74) and BMD (R(2)=0.153, p=0.23) indicated that the morphological data were not biased by the presence of strontium in bone. The FE simulations demonstrated a 22% (p<0.01) increase of stiffness and 29% (p<0.01) increase in strength compared to controls. The magnitudes were greater, but the relative differences were similar when the entire intact vertebra was modeled compared to the vertebral body alone. Adjusting the FE models to account for differences in intrinsic bone tissue quality between control and treated animals resulted in an even higher bone strength with strontium ranelate. Furthermore, load transfer in strontium ranelate treated animals shifted from an equal distribution between cortical and trabecular compartments to more load being supported by the trabecular bone (a shift of 8%, p<0.02). Tissue-level stresses were reduced on average (-7%, p<0.01) and more homogeneously distributed. Together, these findings indicated that, independently from bone strontium content, microarchitectural adaptations played a major role in the increased bone strength associated with strontium ranelate exposure and that the changes in load distribution resulted in patterns that were more favorable to resisting fracture.     

Calculated stress-shielding in the distal femur after total knee replacement corresponds to the reported location of bone loss

This study sought to determine the similarities between features of calculated stress-shielding and observed bone loss in the distal femur after total knee replacement. Stress-shielding was determined by comparing the magnitudes and distributions of strain energy density, calculated using three-dimensional finite element models of the intact bone, the bone after total knee replacement with bonding assumed at all prosthesis-bone interfaces, and the bone after total knee replacement with bonding assumed only at the distal interface. The loading condition simulated static lifting with the knee flexed at 45°, producing tibiofemoral and patellofemoral joint reactions of 900 and 450 N, respectively. The maximum magnitudes of strain energy density calculated using the total knee replacement models were less than 15% of the corresponding magnitudes from the intact bone model. The greatest difference was found to occur at the anterior distal corner of the femur, suggesting this location as the one most vulnerable to stress-shielding. Clinically observed bone loss after total knee replacement frequently occurs at this location. At the anterior distal corner, the calculated magnitudes for the two total knee replacement models were similar, suggesting that stress-shielding at this location was not reduced by limiting fixation only to the distal interface. Although the study corresponded to one loading condition and one geometry of the total knee replacement femoral component with the inherent limitations of model calculations, the results suggest a possible scenario for stress-shielding.     

Changes in bone mineral density of the distal femur following uncemented total knee arthroplasty

The aim of the study was to quantitate changes in bone mineral density (BMD) in the distal femur following uncemented porous-coated total knee arthroplasty. Eight patients with total knee arthroplastics (PCA Primary, Howmedica. Rutherford, NJ) (female:male ratio, 6:2; mean age, 70 years; range, 51–77 years) were scanned by dual-photon absorptiometry within 3 months after surgery and at 2 years. An average decrease of 36% (P = .01) was found in BMD behind the anterior flange of the femoral prosthesis. Proximal to the fixation pegs, BMD increased by 22% (P = .12), but behind the posterior flange of the femoral component, BMD remained unchanged (P = .53). Stress shielding anteriorly in the distal femur occurred in all patients examined 2 years after surgery, and the increase in BMD proximal to the fixation pegs was probably a result of increased and altered mechanical loading.     

Hardness, an indicator of the mechanical competence of cancellous bone

Hardness and calcium content in compact bone are strongly related. Variation in Young's modulus is produced mainly by variations in mineralisation. Therefore, there should be a relationship between hardness and Young's modulus. We demonstrate this. The calcium content of cancellous bone and adjacent compact bone in several species shows little difference, the cancellous bone having approximately 10% less calcium. The hardness of cancellous bone in Bos is approximately 12% less than that of adjacent compact bone, and the calcium is approximately 2% less. These lines of evidence make it unlikely that the Young modulus of cancellous bone material is much different from that of compact bone. Similar evidence suggests that the yield stress of cancellous bone is similar to that of adjacent compact bone.     

股骨远端肿瘤性缺损两种不同内固定方法的有限元分析

目的比较股骨远端骨肿瘤手术中两种不同内固定重建方法的生物力学差别,为临床选择更理想的内固定方法提供理论依据。方法模拟股骨远端骨肿瘤瘤段切除病例,分别采用锁定钢板和交锁髓内钉内固定方法进行重建,建立该模型三维有限元模型,导入ABAQUS软件系统进行有限元分析,当给予平行于股骨长轴轴向压缩700N情况下,比较锁定钢板和交锁髓内钉的位移和应力分布情况。结果两组模型应力均未达到屈服应力,锁定钢板的应力分布比较均匀,接近正常值,最大应力为50 Mpa,股骨头最大位移为2.9 mm。髓内钉的最大应力为85 Mpa,股骨头最大位移为3.8 mm。结论锁定钢板和交锁髓内钉都能用于股骨远端骨肿瘤切除后的重建手术,锁定钢板比交锁髓内钉更稳定,刚度更大。     

股骨上段有限元几何模型的建立与分析

目的建立股骨骨结构三维有限元模型并对其进行分析以指导临床工作。方法在Mimics10.1中直接读取符合Dicom 3.0标准的股骨原始CT数据,经阈值设定、区域增长及形态学操作等生成股骨初始3D模型,后期结合有限元软件ANSYS12.1生成最终的三维有限元网格模型,然后在ANSYS12.1中分别对应用Mimics得到的模型进行分析。结果应用Mimics10.1和Ansys12.1软件建立股骨有限元模型,外形逼真、计算精确。结论 Mimics10.1软件能直接与Ansys12.1软件进行对接,并能根据CT值直接赋值使股骨上段三维有限元模型的建立更加快捷、精确。     

Fixation of experimental osteotomies of the distal femur in rabbits with bone cement and cyanoacrylate

Summary A distal femoral osteotomy was fixed with liquid cyanoacrylate and bone cement in 25 rabbits. Follow-up was done at 1, 3, 6, 12, and 24 weeks. The distal portion of each femur was removed, fixed in alcohol, embedded in methylmethacrylate, sawed to 80 m thickness for OTC-fluorescence study and microradiography, and cut to 5-m sections for histological analysis. Radiological and careful microscopic (OTC labeling, microradiographic, and histological) studies showed healing of the osteotomies during the first 6 weeks after operation. However, at 12 and 24 weeks' follow-up only four of ten osteotomies had healed. According to these observations it is obvious that fixation of an osteotomy of the cancellous bone with bone cement and cyanoacrylate does not provide sufficient stability for successful healing.

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Zusammenfassung Die distalen Femurosteotomien von 25 Kaninchen wurden mit Zyanoakrylat und Knochenzement fixiert. Die Nachuntersuchungen fanden nach 1, 3, 6, 12 and 24 Wochen statt. Der distale Teil von jedem Oberschenkelknochen wurde entnommen, in Alkohol fixiert, in Methylmethacrylat gegossen und für die histologischen Studien auf 5 m Dicke geschnitten und für die OTC-Studien und Microradiographie auf 80 m gesägt. Die radiologischen und genauen mikroskopischen (OTC, Mikroradiographie, Histologic) Untersuchungen zeigten, daß die Osteotomien während den ersten sechs Wochen heilten. Später dagegen waren die Resultate ungenügend, denn nur 4 von 10 Osteotomien waren nach 12 and 24 Wochen geheilt. Auf Grund dieser Resultate ist zu schlieBen, daB eine genügend stabile Osteotomie des spongiösen Knochens durch Fixation mit Knochenzement and Zyanoakrylat nicht erreicht und somit die Heilung gestört wurde.

     

Clinical cone beam computed tomography compared to high-resolution peripheral computed tomography in the assessment of distal radius bone

Summary

Clinical cone beam computed tomography (CBCT) was compared to high-resolution peripheral quantitative computed tomography (HR-pQCT) for the assessment of ex vivo radii. Strong correlations were found for geometry, volumetric density, and trabecular structure. Using CBCT, bone architecture assessment was feasible but compared to HR-pQCT, trabecular parameters were overestimated whereas cortical ones were underestimated.

Introduction

HR-pQCT is the most widely used technique to assess bone microarchitecture in vivo. Yet, this technology has been only applicable at peripheral sites, in only few research centers. Clinical CBCT is more widely available but quantitative assessment of the bone structure is usually not performed. We aimed to compare the assessment of bone structure with CBCT (NewTom 5G, QR, Verona, Italy) and HR-pQCT (XtremeCT, Scanco Medical AG, Brüttisellen, Switzerland).

Methods

Twenty-four distal radius specimens were scanned with these two devices with a reconstructed voxel size of 75 μm for Newtom 5G and 82 μm for XtremeCT, respectively. A rescaling-registration scheme was used to define the common volume of interest. Cortical and trabecular compartments were separated using a semiautomated double contouring method. Density and microstructure were assessed with the HR-pQCT software on both modality images.

Results

Strong correlations were found for geometry parameters (r?=?0.98–0.99), volumetric density (r?=?0.91–0.99), and trabecular structure (r?=?0.94–0.99), all p?<?0.001. Correlations were lower for cortical microstructure (r?=?0.80–0.89), p?<?0.001. However, absolute differences were observed between modalities for all parameters, with an overestimation of the trabecular structure (trabecular number, 1.62?±?0.37 vs. 1.47?±?0.36 mm^?1) and an underestimation of the cortical microstructure (cortical porosity, 3.3?±?1.3 vs. 4.4?±?1.4 %) assessed on CBCT images compared to HR-pQCT images.

Conclusions

Clinical CBCT devices are able to analyze large portions of distal bones with good spatial resolution and limited irradiation. However, compared to dedicated HR-pQCT, the assessment of microarchitecture by NewTom 5G dental CBCT showed some discrepancies, for density measurements mainly. Further technical developments are required to reach optimal assessment of bone characteristics.

     

Regional analysis of bone mineral density in the distal femur and proximal tibia using peripheral quantitative computed tomography in the ratin vivo

The use of peripheral quantitative computed tomography (pQCT) was investigated for the measurement of volumetric bone mineral density (BMD) in mg·cm⁻³. Two studies were undertaken. In the first study, the precision of pQCTin vivo andex vivo was tested at 14 weeks postovariectomy (OVX). In the second study, the efficacy of a standard antiresorptive treatment, 17β-estradiol (E2), was tested 6 weeks post-OVX. The precision for total (compact plus trabecular) BMD was 1.3–1.9%, and that for trabecular BMD was 2.4–2.7%. There was excellent agreement between trabecular BMD measurementsin vivo andex vivo (r=0.91). Significant reductions in trabecular BMD were observedin vivo at 14 and 6 weeks following ovariectomy in the femur, in each study. The loss of trabecular BMD depended on slice location, and varied from 0 to 22% at 6 weeks, and from 0 to 26% at 14 weeks (P<0.001, at the affected locations). The antiresorptive effect of treatment was demonstrated in the 6-week study: there was no significant difference in BMD between sham-operated and E2-treated OVX rats.     

Current concepts in fractures of the distal femur

This paper describes current treatment strategies of distal femoral fractures as well as their evidence based rationale. The treatment of distal femoral fractures has improved with the evolution of plating and nailing technologies. The commonly selected surgical approaches are outlined and surgical treatment techniques including both internal and external fixation are discussed.     

Feasibility of in vivo structural analysis of high-resolution magnetic resonance images of the proximal femur

Previously, high resolution MRI to assess bone structure of deep-seated regions of the skeleton such as the proximal femur was substantially limited by signal-to-noise ratio (SNR). With the advent of new optimized pulse sequences in MRI at 1.5 T and 3 T, it may now be possible to depict and quantify the trabecular microarchitecture in the proximal femur. The purpose of this study was to investigate the feasibility of assessing trabecular microstructure of the human proximal femur in vivo with MR imaging at 1.5 T and 3 T. MR images of six young, healthy male and female subjects were acquired using standard clinical 1.5-T and high-field 3-T whole-body MR scanners. Using a T2/T1-weighted 3D FIESTA sequence (and a 3D FIESTA-C sequence at 3 T to avoid susceptibility artifacts) a resolution of 0.234 × 0.234 × 1.5 mm³ was achieved in vivo. Structural parameters analogous to standard bone histomorphometry were determined in femoral head and trochanter regions of interest. Bone mineral density (BMD) measurements were also obtained using dual-energy X-ray absorptiometry (DXA) for the femoral trochanter in the same subjects. The bone structure of the proximal femur is substantially better depicted at 3 T than at 1.5 T. Correlation between the structural parameters obtained at both field strengths was up to R =0.86 for both the femoral head and the trochanteric region. However, the resolution of the images limits the application of 3D structural analysis, making the assessment more akin to 2D textural measures, which may be correlated to histomorphometric but are not identical measures. This feasibility study establishes the potential of MRI as a means of imaging proximal femur structure, and improvements in technique and resolution enhancements are warranted.