Numerical model to predict the longterm mechanical stability of cementless orthopaedic implants

The objective of this research was to develop a purely biomechanical model, intended to predict the long-term secondary stability of the implant starting from the biomechanical stability immediately after the operation. A continuous rulebased adaptation scheme was formulated as a dynamic system, and the work verified if such a model produced unique and clinically meaningful solutions. It also investigated whether this continuous model provided results comparable with those of a simpler, discrete-states model used in a previous study. The proposed model showed stable convergence behaviour with all investigated initial conditions, with oscillatory behaviour limited to the first steps of the simulation. The results obtained with the wide range of initial conditions support the hypothesis of the existence and uniqueness of the solution for all initial conditions. The differences between the continuous model and the simpler and more efficient finite-states model were found to be extremely modest (less than 4% over the predicted bonded area). Because of these minimal differences, the use of the much faster finite-states model is recommended to investigate asymptotic conditions, and the continuous model described should be used to investigate the evolution over time of the adaptive process.     

Observations of convergence and uniqueness of node-based bone remodeling simulations

Some investigators have indicated that mathematical theories and computational models of bone adaptation may not converge and that the density solutions from such simulations are dependent on the initial density distribution In this study, two-dimensional finite element models were used to investigate the effect of initial density distribution on the final density distribution produced using a node-based bone remodeling simulation. The first model was a generic long bone, and the second was a proximal femur. For each model, we conducted time-dependent, node-based, linear rate-law bone remodeling simulations. Five initial density conditions were used with the generic long bone and three with the proximal femur. Remodeling simulations were performed, and the largest average nodal density differences at the end of the simulations were 0.000010 g/cm³ and 0.000006 g/cm³ for the generic long bone and proximal femur models, respectively. Results illustrate that, for a given set of loads and a given finite element model, the node-based bone adaptation algorithm can yield a unique density distribution. In conjunction with previous studies, this finding suggests that uniqueness of the density solution is dependent on both the mathematical theory and the computational implementation.     

模拟腰部推拿手法建立“腰-盆-髋”有限元模型

背景：对局部椎体或整个脊柱进行推拿手法的有限元分析具有一定的局限性。 目的：通过建立“腰-盆-髋”有限元模型对腰部推拿手法进行相关生物力学分析。 方法：利用螺旋CT 数据通过Mimics 10.01 建立具有高度几何相似性的腰椎、骨盆和股骨近端复合体骨骼的面模型,利用geomagic9精修模型,在hypermesh10.0中划分网格,添加椎间盘和主要韧带。并对有限元模型各部件进行材料属性赋值。利用有限元分析软件模拟腰椎推拿手法三工况加载,计算特征部位位移、最大应变及应力。 结果与结论：有限元模型在三工况载荷下的特征部位应力、应变值基本能够反映“腰-盆-髋”特有的力学结构特性,模型的仿真性较好。在近似的几何外形下,据生物力学资料报道的材料赋值建模保证了有限元模型计算的正确性;模拟接近生理状况下的边界及载荷条件进行计算可以确保结果的准确性。     

Evaluation of the role of ligaments, facets and disc nucleus in lower cervical spine under compression and sagittal moments using finite element method.

Cervical spinal instability due to ligamentous injury, degenerated disc and facetectomy is a subject of great controversy. There is no analytical investigation reported on the biomechanical response of cervical spine in these respects. Parametric study on the roles of ligaments, facets, and disc nucleus of human lower cervical spine (C4-C6) was conducted for the very first time using noninvasive finite element method.A three-dimensional (3D) finite element (FE) model of the human lower cervical spine, consisted of 11,187 nodes and 7730 elements modeling the bony vertebrae, articulating facets, intervertebral disc, and associated ligaments, was developed and validated against the published data under three load configurations: axial compression; flexion; and extension. The FE model was further modified accordingly to investigate the role of disc, facets and ligaments in preserving cervical spine motion segment stability in these load configurations. The passive FE model predicted the nonlinear force displacement response of the human cervical spine, with increasing stiffness at higher loads. It also predicted that ligaments, facets or disc nucleus are crucial to maintain the cervical spine stability, in terms of sagittal rotational movement or redistribution of load. FE method of analysis is an invaluable application that can supplement experimental research in understanding the clinical biomechanics of the human cervical spine.     

Biomechanical robustness of a new proximal epiphyseal hip replacement to patient variability and surgical uncertainties: a FE study

The biomechanical behaviour of current hip epiphyseal replacements is notably sensitive to the typical variability of conditions following a standard surgery. The aim of the present study was to assess the biomechanical robustness to the variability of post-operative conditions of an innovative proximal epiphyseal replacement (PER) hip device featuring a short, curved and cemented stem. The risk of femoral neck fractures, prosthesis fractures and aseptic loosening were assessed through a validated finite element procedure following a systematic approach. Risk changes due to anatomical variations were assessed mimicking extreme conditions in terms of femoral size and level of osteoporosis. Failure risks associated with surgical uncertainties were assessed mimicking extreme conditions in terms of uncertainties on the prosthesis position/alignment, cement-bone interdigitation depth, and friction between the prosthesis and the hosting cavity. The femoral neck strength increased after implantation from 9% to 49% and was most sensitive to changes of the anatomo-physiological variables. The risk of stem fractures was low in all studied configurations. The risk of stem loosening was low and most sensitive to surgical uncertainties. In conclusion, the new device can be considered an effective alternative to current epiphyseal replacements. Care is recommended in a proper seating of the prosthesis in the femur.     

In-vitro biomechanical evaluation of stress shielding and initial stability of a low-modulus hip stem made of β type Ti-33.6Nb-4Sn alloy

Stress shielding-related proximal femoral bone loss after total hip arthroplasty occurs because of the different stiffness of metallic alloy stems and host bone. To overcome this, we fabricated a low-modulus cementless hip stem from β-type Ti-33.6Nb-4Sn alloy (TNS). Then we evaluated its stiffness, stress shielding, and initial stability compared with a similar Ti-6Al-4V alloy stem. Stiffness was determined by axial compression and cantilever-bending tests. Thirteen triaxial strain gages measured cortical strain. Stress shielding was defined as the percentage of intact strain after stem insertion. To evaluate initial stability, displacement transducers measured axial relative displacement and rotation. Intact and implanted femurs underwent single-leg-stance loading. Axial stiffness was 56% lower in the TNS stem than in the Ti-6Al-4V stem, and bending stiffness of the TNS stem decreased gradually from the proximal region to the distal region, being ≤53% that of the Ti-6Al-4V stem, indicating gradation of Young's modulus. The TNS stem decreased stress shielding in the proximal calcar region (A1: 83%, B1: 85% relative to intact cortical strain) without affecting the proximal lateral region (B3: 53%). The initial stabilities of the stems were comparable. These findings indicate that the TNS stem with gradation of Young's modulus minimizes proximal femoral bone loss and biological fixation, improving long-term stability.     

有限元分析股骨颈骨折伴下后方不同程度骨缺损空心螺钉内固定后的稳定性

文题释义：有限元分析：是基于结构力学分析迅速发展起来的一种现代计算方法,通过计算机硬件及软件将载荷、形态、材料结构和力学性能较为复杂的整体划分为有限个简单的单元,进而充分反映整体内外部应力、应变、位移等力学参数的变化情况。通过将股骨近端及空心钉进行有限网格划分,施加载荷后可了解到股骨近端、空心钉每个网格的应力与应变情况。 创伤性股骨头坏死：各类因素引起股骨头血供下降或力学环境改变,导致股骨头内骨小梁坏死塌陷、髋关节疼痛及功能障碍的常见疾病。其中创伤性股骨头坏死与激素性股骨头坏死等不同,生物力学因素在其病情发生发展中发挥重要作用。骨小梁出现“损伤-微骨折-修复”交替反应,超过生理修复负荷,骨小梁修复重塑反应受阻,局部骨小梁走形杂乱无章,这是创伤性股骨头坏死重要的发病机制。 背景：空心螺钉固定为新鲜股骨颈骨折的首选治疗方法,但对于伴有骨缺损的患者,由于股骨近端力学传导及稳定性发生明显改变,易导致内固定物失效、骨折不愈合或延迟愈合等,因此生物力学研究具有重要的临床意义。 目的：利用有限元方法探究骨缺损后股骨近端的生物力学改变,比较不同构型空心螺钉固定内收型股骨颈骨折伴下后方不同程度骨缺损的生物力学效果。 方法：获取一名成年健康男性志愿者股骨近端CT扫描DICOM原始数据,利用MIMICS 10.01软件、Rhino3D NURBS软件制作内收型股骨颈骨折伴后下方不同程度骨缺损模型(无缺损模型、小缺损模型、中缺损模型与大缺损模型),在4组模型中各配置两种构型的空心螺钉(倒三角、正三角),装配完成后进行网格划分、材料属性赋值;通过ABAQUS 6.12软件建立股骨头中心和表面的耦合关系,对所有模型施加缓慢行走时的载荷和约束。 结果与结论：①无缺损模型的股骨颈内侧承受压应力,外侧承受张应力,股骨头应力分布较为均匀,随着股骨颈下后方缺损程度的增加,压力侧和张力侧空心螺钉、空心螺钉尾部及股骨头的应力峰值逐渐上升;②随着缺损程度的增加,空心螺钉压力侧应力峰值逐渐增加,在中、大缺损模型中,倒三角组高于正三角组(P < 0.05),在其余模型中两组之间无差异(P > 0.05);③随着缺损程度的增加,空心螺钉张力侧应力峰值逐渐增加,在无缺损与小缺损模型中,正三角组高于倒三角组(P < 0.05);在大缺损模型中,正三角组低于倒三角组(P < 0.05);在中缺损模型中两组无差异;④随着缺损程度的增加,股骨头应力峰值逐渐增加,3种模型中倒三角组与正三角组均无明显差异(P > 0.05);⑤随着缺损程度的增加,空心螺钉尾部应力峰值逐渐增加,在小、中、大缺损模型中,倒三角组高于正三角组(P < 0.05),在无缺损模型中两组无差异(P > 0.05);⑥结果表明,下后方不同程度骨缺损可显著影响股骨近端力学性能,对于无缺损或缺损程度较小的股骨颈骨折,空心螺钉倒三角构型的生物力学性能优于正三角构型,而对于缺损程度较大的股骨颈骨折,空心螺钉正三角构型的生物力学性能优于倒三角构型。 ORCID: 0000-0001-9190-2904(张成宝) 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     

Improved design of cementless hip stems using two-dimensional functionally graded materials

Increasingly, it is acknowledged that bone resorption around cementless hip implants may cause future problems. The solution is frequently sought in reducing implant stiffness. However, this confronts the designer with a true design conflict: how to reduce the stiffness without excessively loading the proximal bone/prosthesis interface? The aim of this work is to improve the design of cementless hip stem material, using two-dimensional (2D) functionally graded material (FGM) concept in order to solve the above problems. Two models were used in this analysis, using three materials with different elastic moduli, E(1), E(2), and E(3). In model I, the elastic moduli E(1) and E(2) gradually change along the upper stem surface, while E(3) is maintained constant along all the lower surface of the stem. However, in model II, the elastic moduli E(1) and E(2) gradually change along the lower stem surface, while E(3) is maintained constant all along the upper stem surface. It is found that the recommended model is model I, which has three distinct materials of hydroxyapatite, Bioglass, and collagen. The recommended design of 2D FGM is expected to reduce the stress shielding by 91% and 12%, respectively, compared with titanium stem and model II of FGM. It is found that this new design reduces the maximum interface shear stress at the lateral and medial sides of the femur by about 50%, compared with titanium stem. Furthermore, the maximum interface shear stress is reduced by about 17% and 11% at the lateral and medial sides of the femur, respectively, compared with that of model II of FGM.     

全髋关节置换术中臼杯水平位移对股骨侧非骨水泥型假体-骨界面应力影响的有限元分析

目的　利用三维有限元力学分析方法, 研究全髋关节置换术中臼杯水平位移对股骨侧非骨水泥型假体-骨界面应力分布的影响。 方法　选取正常人体的骨盆及股骨为实验对象, 螺旋CT 扫描,利用计算机仿真技术对CT图像进行三维重建,建立髋关节及股骨模型,进行全髋关节置换的模拟手术, 臼杯位置从髋关节旋转中心外侧10mm处起,水平内移,每隔2 mm为一个实验组,至内移至旋转中心内侧10 mm,共分11个实验组。加载关节负荷,观察股骨侧假体-骨界面间的Von Mises应力分布情况, 对结果进行统计分析。 结果　臼杯的水平位移没有改变股骨总体的应力云分布;各组假体-骨界面应力均值（4.728±2.152）-（5.431±2.465）MPa,均值有差异,差异有统计学意义;应力均值、极差、标准差均随内移而降低,呈高度的负相关。近端假体-骨界面的应力变化,与整个股骨的应力变化相似。 结论　假体的水平内移可以降低股骨侧假体-骨界面间的Von Mises应力,内移可以使界面的应力分布更均匀。     

Mechanical and functional assessment of the wrist affected by rheumatoid arthritis: A finite element analysis

Understanding the pathomechanics involved in rheumatoid arthritis (RA) of the wrist provides valuable information, which will invariably allow various therapeutic possibilities to be explored. The computational modelling of this disease permits the appropriate simulation to be conducted seamlessly. A study that underpins the fundamental concept that produces the biomechanical changes in a rheumatoid wrist was thus conducted through the use of finite element method. The RA model was constructed from computed tomography datasets, taking into account three major characteristics: synovial proliferation, cartilage destruction and ligamentous laxity. As control, a healthy wrist joint model was developed in parallel and compared. Cartilage was modelled based on the shape of the articulation while the ligaments were modelled with linear spring elements. A load-controlled analysis was performed simulating physiological hand grip loading conditions. The results demonstrated that the diseased model produced abnormal wrist extension and stress distribution as compared to the healthy wrist model. Due to the weakening of the ligaments, destruction of the cartilage and lower bone density, the altered biomechanical stresses were particularly evident at the radioscaphoid and capitolunate articulations which correlate to clinical findings. These results demonstrate the robust finding of the developed RA wrist model, which accurately predicted the pathological process.     

The effect of time to peak ankle torque on balance stability boundary: experimental validation of a biomechanical model

Pai and Patton (1997), using a biomechanical model, determined a set of feasible center of mass (CM) velocity-position combinations (balance stability boundary) that guarantee upright stability. In their study, the magnitude of the restoring ankle torque was used to study the subject's ability to recover balance. Recent studies have suggested that the ability to maintain a stable posture depends not only on the magnitude of the restoring torque but also on the time to generate this torque. The objectives of the present study were: (1) to build a biomechanical model that predicts the balance stability boundary which includes time to peak ankle torque, (2) to determine the capability of the model to predict successful and failed experimental balance recovery trials, and (3) to compare the predictive capability of the biomechanical model with that of a statistical model (logistic regression). A single-link-plus-foot biomechanical model was used to determine a set of balance stability boundaries, computed from the combination of maximum CM velocity and related CM position, for various times to peak ankle torque. An experiment was conducted to validate the biomechanical model. The participants self-initiated a forward destabilization and were asked to regain balance using an ankle feet-in-place strategy. Also, a forward stepwise logistic regression (predictors: CM position and velocity and time to peak ankle torque) was used to discriminate between successful and failed experimental trials. (1) The outcomes of the biomechanical model confirmed that the time to peak ankle torque drastically constrained the stability boundaries. (2) The biomechanical model predicted 79.9% of the failed experimental trials and 74.5% of the successful experimental trials. (3) The stepwise logistic regression included all independent variables and predicted 57.2% of the failed and 93.7% of the successful experimental trials. Hence, the biomechanical model showed better predictive capability than the statistical model for identifying unsuccessful balance recovery. It is noteworthy that the balance stability boundaries constrained by the speed of ankle torque development predicted the outcome of the experimental trial earlier in the time series than balance stability boundary constrained by constant ankle torque. Overall, the present biomechanical model may serve as an assessment tool to develop specific interventions towards improving a patient's speed of ankle torque development and to possibly reduce falling frequency.     

Hemodynamic assessments of the ascending thoracic aortic aneurysm using fluid-structure interaction approach

Current assessment and management of ascending thoracic aortic aneurysm (ATAA) rely heavily on the diameter of the ATAA and blood pressure rather than biomechanical and hemodynamic parameters such as arterial wall deformation or wall shear stress. The objective of the current study was to develop an accurate computational method for modeling the mechanical responses of the ATAA to provide additional information in patient evaluations. Fully coupled fluid structure interaction simulations were conducted using data from cases with ATAA with measured geometrical parameters in order to evaluate and analyze the change in biomechanical responses under normotensive and hypertensive conditions. Anisotropic hyperelastic material property estimates were applied to the ATAA data which represented three different geometrical configurations of ATAAs. The resulting analysis showed significant variations in maximum wall shear stress despite minimal differences in flow velocity between two blood pressure conditions. Additionally, the three different ATAA conditions identified different aortic expansions that were not uniform under pulsatile pressure. The elevated wall stress with hypertension was also geometry-dependent. The developed models suggest that ATTA cases have unique characteristic in biomechanical and hemodynamic evaluations that can be useful in risk management.     

股骨转子间骨折不同外侧壁分型髓内钉治疗的有限元分析

背景：目前针对外侧壁破损型股骨转子间骨折的手术内固定方式存在争议,以股骨近端防旋髓内钉固定为主流方案,不同外侧壁分型的股骨转子间骨折髓内固定的生物力学研究较少。目的：通过有限元分析比较股骨近端防旋髓内钉治疗不同外侧壁分型股骨转子间骨折的生物力学特点,探讨外侧壁对股骨转子间骨折内固定的影响。方法：选择1例健康老年女性患者,根据股骨近端CT扫描数据,应用Mimics 21.0,Geomagic Wrap,Creo 6.0,Abaqus 2020软件建立股骨近端和股骨近端防旋髓内钉的三维有限元模型,模拟外侧壁稳定型、危险型及破裂型股骨转子间骨折,建立股骨近端防旋髓内钉内固定装配模型。观察在静止及行走2种状况下赋予同等载荷时3种骨折内固定模型的等效应力及位移分布云图。结果与结论：(1)A3.3型股骨转子间骨折在动态载荷时最大等效应力及位移均最大,最大等效应力约为A2.3型的2倍,A1.3型的2.7倍,最大等效位移约为A2.3型的1.5倍,A1.3型的3倍,静态时各型差别不明显;(2)动静态载荷时股骨颈、骨折端及主钉处等效应力A3.3型较A1.3和A2.3型增大,以主钉处明显;(3)动态载荷时股...     

张应力对深筋膜力学特性影响的实验研究

目的：探讨肢体延长过程中张应力对深筋膜力学特性的影响。方法：建立新西兰大白兔双侧胫骨胶体延长动物模型,术后第７ｄ开始延长,延长速度为１ｍｍ／ｄ和２ｍｍ／ｄ,每１２ｈ一个增量,延长率为腔骨长度的１０％和２０％。将正常小腿深筋膜和不同延长速度及延长率作用下的深筋膜制成３０ｍｍ×１０ｍｍ的筋膜条,在室温（１３．２℃）和５ｍｍ／ｍｉｎ的拉伸速度下,以Ｉｎｓｔｒｏｎ１１２２型万能拉伸仪进行单轴拉伸实验,在５次加载－卸载的预调后,拉伸深筋膜直至破裂,记录其载荷－位移曲线,比较正常和肢体延长后各实验组的载荷－位移曲线。结果：正常深筋膜载荷－位移曲线显示典型的胶原组织的载荷－位移规律,肢体延长后的筋膜基本上保持了这一特点,其中以速度延长１ｍｍ／ｄ,延长率２０％的筋膜的载荷－位移曲线与正常筋膜的曲线最为接近。正常的深筋膜极限应变为１４．１１％,极限载荷为２．６９Ｎ,肢体延长后深筋膜的极限载荷有所增加（Ｐ＜０．００１）。结论：肢体延长过程中不同的延长速度、延长率对深筋膜载荷－位移曲线有着显著的影响,延长速度１ｍｍ／ｄ,延长率２０％的载荷－位移曲线最接近正常。     

Challenges in Hip Joint Modeling for a Patient with Proximal Femoral Focal Deficiency

We were presented with a technical challenge driven by a clinical need. A patient with proximal femoral focal deficiency required gait analysis, but our typical biomechanical model [Vicon Clinical Manager (VCM)] would not have correctly identified his abnormal right hip center (RHIP). His underdeveloped right femur was fused to his ileum, his anatomical knee functioned as his right hip, and an above-knee prosthesis provided functional knee and ankle joints. During a special calibration, we estimated the global location of RHIP as the center of the femoral epicondyles, also identifying the global location of pelvic markers. These data were used in equations after Davis et al.⁴ to establish local coordinates for RHIP. We used a system of three simultaneous equations to solve for input to VCM that would reproduce this location for RHIP. This procedure allowed for inverse dynamics in VCM, and showed the emergence of an abduction moment at the right hip postoperatively, that exceeded changes predicted by sensitivity analyses. Although our clinical need was met, we concluded that a better approach would have involved full implementation of custom models to reflect abnormal patient anatomy. © 2003 Biomedical Engineering Society. PAC2003: 8719St, 8710+e     

无柄解剖形人工髋关节生物力学实验研究

本实验对一种新型无柄解剖形人工髋关节 (英文名称为 A- Fix TM :Non- stem med Anatomical Total HipProsthesis)仿真临床置换术下的早期 (无骨水泥固定 )和后期 (用骨水泥固定模拟骨组织自然生长 )状态 ,进行生物力学实验研究 ,并对照正常自然股骨和股骨颈对实验结果进行归一化系数分析比较 .结果显示 ,无柄人工髋置换术后无骨水泥固定态和骨水泥固定态的股骨头垂直位移相似 ,均略大于正常股骨态的位移。置换后无骨水泥固定态和骨水泥固定态的应变分布特征也相同 ,但与正常态相比 ,股骨颈的受拉侧和受压侧的应变值都明显降低 ,并且变化平缓。相对于正常态而言 ,置换后无骨水泥固定态的安全系数在受拉侧提高 13% ,受压侧提高 2 7.6 % ;置换后骨水泥固定态的安全系数在受拉侧提高 2 9.6 % ,受压侧提高 2 2 .1%。置换前后股骨头最大扭转角都小于 0 .3°,无骨水泥固定态的扭转角是正常态的 0 .0 2倍 ,骨水泥固定态的扭转角是正常态的 0 .0 1倍。研究表明新型无柄解剖形人工髋关节具有低应力 ,高强度和小变形 ,抗松动 ,高刚度等一系列优异的力学特性 ,为其临床应用和推广 ,提供可靠的力学依据。     

Intrabody application of eptotermin alpha enhances bone formation in osteoporotic fractures of the lumbar spine; however,fails to increase biomechanical stability – results of an experimental sheep model

Abstract

This study analyses the effect of eptotermin α application into fractured vertebrae. It is hypothesized that eptotermin α is capable to enhance bony healing of the osteoporotic spine. In 10 Merino sheep osteoporosis induction was performed by ovariectomy, corticosteroid therapy and calcium/phosphorus/vitamin D-deficient diet; followed by standardized creation of lumbar vertebral compression fractures (VCFs) type A3.1 and consecutive fracture reduction/fixation using expandable mesh cages. Randomly, intravertebral eptotermin α (G1) or no augmentation was added (G2). Macroscopic, micro-CT, and biomechanical evaluation assessed bony consolidation two months postoperatively: Micro-CT data revealed bony consolidation for all cases with significant increased callus development for G2 (60%) and BV/TV (bone volume/total volume 73.45%, osteoporotic vertebrae 35.76%). Neither group showed improved biomechanical stability. Eptotermin α enhanced mineralisation in VCFs in an experimental setup with use of cementless augmentation via an expandable cage. However, higher bone mineral density did not lead to superior biomechanical properties.     

Supporting adherence and healthy lifestyles in leg ulcer patients: systematic development of the Lively Legs program for dermatology outpatient clinics

OBJECTIVES: The objective of our project was to develop a lifestyle program for leg ulcer patients at outpatient clinics for dermatology. METHODS: We used the intervention-mapping (IM) framework for systematically developing theory and evidence based health promotion programs. We started with a needs-assessment. A multidisciplinary project group of health care workers and patients was involved in all five IM steps; formulating proximal program objectives, selecting methods and strategies, producing program components, planning for adoption and implementation and planning for evaluation. Several systematic literature reviews and original studies were performed to support this process. RESULTS: Social Cognitive Theory was selected as the main theory behind the program 'Lively Legs' and was combined with elements of Goal-Setting Theory, the precaution adoption model and motivational interviewing. The program is conducted through health counseling by dermatology nurses and was successfully pre-tested. Also, an implementation and evaluation plan were made. CONCLUSION: Intervention mapping helped us to succeed in developing a lifestyle program with clear goals and methods, operational strategies and materials and clear procedures. PRACTICE IMPLICATIONS: Coaching leg ulcer patients towards adherence with compression therapy and healthy lifestyles should be taken on without delay. Systematic development of lifestyle programs for other patient groups should be encouraged.     

强化螺钉骨水泥髓内钉固定治疗重度骨质疏松性股骨转子间Evans Ⅱ型骨折的生物力学有限元分析

目的 通过有限元分析探讨强化螺钉骨水泥髓内钉固定治疗重度骨质疏松性股骨转子间Evans Ⅱ型骨折的生物力学效果。方法 选取新疆医科大学第一附属医院骨科中心2020年10月5日收治的1例重度骨质疏松性Evans Ⅱ型左股骨转子间骨折患者的CT资料。患者女,73岁,身高160 cm,体质量56 kg。将患者髋部及股骨的CT数据在Mimics 20软件和 Geomagic Wrap 2017软件中进行提取、优化,得到右侧股骨三维模型;运用Solidworks 2017软件画出内固定模型并参考标准的手术技术进行股骨模型装配。将装配好的模型在3-Matic软件中进行截骨得到Evans Ⅱ型股骨转子间骨折模型,截取螺钉近端周围的部分松质骨设置为骨水泥部件,分别构建A模型[普通股骨近端防旋髓内钉（PFNA）内固定模型]、B模型（钉道强化PFNA内固定模型）及C模型（强化螺钉内固定模型）。按照患者CT数据及内固定的材质标准赋予相应的参数、条件,以及人体力学在股骨的受力及患者的体质量赋予载荷值分别储存,并利用ansys 2019软件中的Explicit Dynamics模块进行分析。观察指标：对比3种模型螺钉在股骨近端的切割程度、股骨颈向内翻角度、股骨颈内旋角度、应力在股骨的分布情况,以及股骨头近端移位情况。结果 3种模型螺钉在股骨近端骨水泥表面均由螺旋刀片四周向远端发生切割、形变、沉陷,程度由轻到重依次为C、B、A模型。股骨颈骨块内翻角度和股骨颈旋转角度,A、B模型均分别为0.37°和0.16°,C模型稍占优势分别为0.32°和0.15°。A模型应力主要集中在螺旋刀片和主钉交接处,B、C模型相较于A模型发生了应力转移,分散向骨水泥部位;C模型股骨骨折部分发生最大移位的距离为5.8 mm,相较于A、B模型（均为6.7 mm）减小。结论 强化螺钉内固定治疗重度骨质疏松性股骨转子间Evans Ⅱ型骨折较普通股骨PFNA及钉道强化PFNA具有更好的生物力学效果。     

Effect of rotator cuff dysfunction on the initial mechanical stability of cementless glenoid components

The functional outcome of shoulder replacement is related to the condition of the rotator cuff. Rotator cuff disease is a common problem in candidates for total shoulder arthroplasty; this study relates the functional status of the rotator cuff to the initial stability of a cementless glenoid implant. A 3D finite element model of a complete scapula was used to quantify the effect of a dysfunctional rotator cuff in terms of bone-implant interface micromotions when the implant is physiologically loaded shortly after surgery. Four rotator cuff conditions (from fully intact to progressively ruptured rotator cuff tendons) as well as two bone qualities were simulated in a model. Micromotions were significantly larger in the worst modeled cuff dysfunction (i.e. the supraspinatus and infraspinatus tendons were fully dysfunctional). Micromotions were also significantly different between conditions with healthy and poor bone quality. The implant’s initial stability was hardly influenced by a dysfunctional supraspinatus alone. However, when the infraspinatus was also affected, the glenohumeral joint force was displaced to the component’s rim resulting in larger micromotions and instability of the implant.