基于损伤修复理论的各向异性骨再造自我组织控制模型

Wolff定律指出 :骨能够响应力学激励来改变其表观密度和骨小梁分布的方向 ,表明骨再造是各项异性行为。本研究基于各项异性损伤修复理论并结合自我组织控制模型 ,提出更符合骨再造实际生理行为的基于损伤修复理论的各向异性自我组织控制骨再造模型 ,并以股骨近端为例进行了模拟 ,得到的结果在密度分布与主应力迹线分布上和实际都非常一致。     

Bone remodeling regulation under unloading conditions: Numerical investigations

The present paper addresses the following question: can a simple regulatory bone remodeling model predict effects of unloading conditions on the trabecular bone morphology? In an attempt to answer this question, rat tail-suspension was chosen as a model that mimics the microgravity environment. Over 23 days, histomorphometric analysis was carried out on cross-sections of tibias of the suspended animals. The slices were digitalized and images discretized to obtain osteocyte distribution and apparent bone density. Based on these experimental data, finite element simulations were conducted to evaluate the bone loss and the change in trabecular architecture similar to those observed after a spaceflight. The numerical model is driven by a remodeling law that takes into account the nonuniform osteocyte distribution that may itself provide mechanoreception. We used the bone density rate of change from the remodeling theory and a time stepping algorithm witch are implemented in a finite element software.This approach takes into account the unloading effects on bone remodeling process and permits to confront experimental and numerical data. We showed that there is a good agreement between these data, particularly at the beginning of the simulated bone mass loss during the rat tail-suspension experiment. Indeed, we obtained a variation of 5.25% at day 7 (D7), 2.09% at day 13 (D13) and finally, 51.03% at day 23 (D23). Despite that last variation, the proposed theoretical model can be suitable to simulate the alteration of bone mineral density under the specific unloading conditions of the rat tail-suspension model.     

Numerical Modeling of Long Bone Adaptation due to Mechanical Loading: Correlation with Experiments

The process of external bone adaptation in cortical bone is modeled mathematically using finite element (FE) stress analysis coupled with an evolution model, in which adaptation response is triggered by mechanical stimulus represented by strain energy density. The model is applied to experiments in which a rat ulna is subjected to cyclic loading, and the results demonstrate the ability of the model to predict the bone adaptation response. The FE mesh is generated from micro-computed tomography (μCT) images of the rat ulna, and the stress analysis is carried out using boundary and loading conditions on the rat ulna obtained from the experiments [Robling, A. G., F. M. Hinant, D. B. Burr, and C. H. Turner. J. Bone Miner. Res. 17:1545–1554, 2002]. The external adaptation process is implemented in the model by moving the surface nodes of the FE mesh based on an evolution law characterized by two parameters: one that captures the rate of the adaptation process (referred to as gain); and the other characterizing the threshold value of the mechanical stimulus required for adaptation (referred to as threshold-sensitivity). A parametric study is carried out to evaluate the effect of these two parameters on the adaptation response. We show, following comparison of results from the simulations to the experimental observations of Robling et al. (J. Bone Miner. Res. 17:1545–1554, 2002), that splitting the loading cycles into different number of bouts affects the threshold-sensitivity but not the rate of adaptation. We also show that the threshold-sensitivity parameter can quantify the mechanosensitivity of the osteocytes.     

应变能密度作控制变量的骨干表面再造—理论预测

用应变能密度作控制变量，其改变量作再造动力，在常压下，将骨干抽象成圆柱形筒，进行骨干表面再造的理论预测。推出的控制内外表面移动的非线性微分方程组的解有８ 种类型，对应的压力值和内外表面再造率系数有４５ 种。它包括了Ｃｏｗｉｎ 用应变作控制变量的理论预测的解。尽管模型与实际相比有一定局限性，但仍能与典型的动物试验结果相一致。从而从理论上说明了用应变能密度作控制变量的适应性骨再造的可靠性。     

Can the contra-lateral limb be used as a control with respect to analyses of bone remodelling?

Bone loss may result from remodelling initiated by implant stress protection. Quantifying remodelling requires bone density distributions which can be obtained from computed tomography scans. Pre-operative scans of large animals however are rarely possible. This study aimed to determine if the contra-lateral bone is a suitable control for the purpose of quantifying bone remodelling. CT scans of 8 pairs of ovine tibia were used to determine the likeness of left and right bones. The deviation between the outer surfaces of the bone pairs was used to quantify geometric similarity. The density differences were determined by dividing the bones into discrete volumes along the shaft of the tibia. Density differences were also determined for fractured and contra-lateral bone pairs to determine the magnitude of implant related remodelling. Left and right ovine tibiae were found to have a high degree of similarity with differences of less than 1.0 mm in the outer surface deviation and density difference of less than 5% in over 90% of the shaft region. The density differences (10–40%) as a result of implant related bone remodelling were greater than left-right differences. Therefore, for the purpose of quantifying bone remodelling in sheep, the contra-lateral tibia may be considered an alternative to a pre-operative control.     

一种力学-生物学因素耦联的松质骨骨质疏松过程计算模型

目的是研究力学因素和生物学因素在松质骨骨质疏松过程中的作用。根据骨重建的生理过程，在基本多细胞单位（BMUs）层次建立了一个力学因素和生物学因素耦联的，带有时间历程的松质骨骨质疏松过程计算模型。通过调整模型中的力学因素和生物学因素，模拟了妇女绝经期骨量变化过程，其模拟结果与Recker等临床观测结果非常接近。可见，本研究提出的松质骨骨质疏松过程计算模型可以很好地描述松质骨的骨质疏松过程，为中老年群体防治骨质疏松提供理论基础和计算分析方法。     

不同力学激励对骨重建数值模拟的影响

目的研究采用应变能密度、等效应力、等效应变3种不同力学激励对骨重建数值模拟结果的影响。方法建立股骨近端的二维有限元模型,基于力学稳态理论的重建控制方程并结合有限元法,分别用3种不同力学激励模拟股骨近端的内部结构及密度分布,并与CT数据计算得到的骨密度值进行定量分析比较。结果 3种力学激励模拟得到的重建结果均能反映出股骨近端的主要特征结构,但采用等效应力作为激励时得到的股骨密度曲线图的趋势和数值都与CT图像数据更为一致。结论在骨重建力学调控机制中,应力可能起主导作用。准确预测和模拟骨重建过程将对矫形外科、骨伤治疗、人工假体的优化和个体化设计等临床实践提供理论依据。     

The reaction of different skeletal sites to metabolic bone disease — A micromorphometric study

Summary It is unknown whether histomorphometric parameters of bone surface remodelling change uniformly throughout the skeleton in metabolic bone disease.In patients without skeletal disease (n=8), in patients with chronic renal failure (n=13) and in patients with malignant tumors (n=11), post mortem bone samples were taken from the core of the 5th lumbar vertebra, from the iliac crest, from the femural head and from the interepicondylar portion of the distal femur. Histomorphometric analysis was carried out in undecalcified sections stained after Masson-Goldner. The dispersion of histomorphometric parameters between the different skeletal sites (cancellous bone) was evaluated by analysis of variance.There existed marked differences in the surface extension of the histomorphometric parameters which are related to bone remodelling, suggesting marked differences in the local remodelling rates (iliac crest > lumbar vertebra > femural head > distal femur).In patients with bone disease all histomorphometric parameters changed uniformly throughout the skeleton with the exception of inactive osteoid.The study shows that in metabolic bone disease local factors do not interfere with remodelling in response to systemic factors. It also provides evidence that bone biopsy samples from iliac crest spongiosa reflect with reasonable accuracy the changes occurring elsewhere in the skeleton, although inactive osteoid may accumulate in the iliac crest out of proportion to its increase in low-turnover sites.With the support of the Deutsche Forschungsgemeinschaft     

Metaphyseal sleeves in revision total knee arthroplasties: Computational analysis of bone remodeling

BackgroundMetaphyseal sleeves help maintain long term stability and reduce revision rate for aseptic loosening in total knee arthroplasty (TKA) revision. However, their performance regarding bone remodeling is still poorly known for the long term. This study aimed to investigate the impact of metaphyseal sleeves on the bone remodeling of the tibia.MethodsFive finite element models of a female tibia with different implant configurations (regarding stem length and metaphyseal sleeve application) were developed. Loading conditions included joint reaction force, muscle, and tibia-fibula loads from 6 instances of the gait cycle. The bone remodeling model applied was adapted to the subject under analysis by selecting the bone remodeling parameters that best replicated the bone density distribution of the tibia estimated from the CT data. Changes in bone density after TKA were evaluated in 8 regions of interest.ResultsGlobal bone loss ranged from −31.16%, in 115 mm stemmed configurations, to −20.93%, in 75 mm stemmed configurations. Apart from the lateral and posterior regions in the proximal tibia, whose bone loss reduced and increased, respectively, due to the incorporation of a metaphyseal sleeve, changes in bone density were similar with and without a metaphyseal sleeve for each stem length.ConclusionThe results suggest that bone remodeling of the tibia is not critically affected by the incorporation of metaphyseal sleeves. Considering that sleeves are believed to present a favorable clinical outcome in stability and osseointegration, reducing the revision rate for aseptic loosening, their advantages seem to outweigh their disadvantages regarding bone remodeling.     

雌激素干预骨质疏松大鼠牙槽骨改建过程中白细胞介素1的表达

背景：目前大鼠是骨质疏松研究中使用最多的模型动物,其中大鼠去卵巢动物模型应用最广泛,雌性大鼠在卵巢切除后,其骨质变化和给予雌激素后的反应与人相似。 目的：建立骨质疏松拔牙创愈合的大鼠动物模型,研究雌激素应用对骨质疏松大鼠牙槽骨中白细胞介素1分布及表达的影响。 方法：选用65只纯种3月龄雌性大鼠,按随机数字表法分为2组,骨质疏松模型组40只大鼠在全麻下摘除双侧卵巢,25只假手术组摘除卵巢周围与之大小相同的脂肪组织,常规饲养8周以建立大鼠骨质疏松模型。造模成功后全麻拔除大鼠左侧上颌磨牙,病理彩色图像分析仪分析颌骨变化。在骨质疏松模型组中随机抽取15只皮下注射苯甲酸雌二醇作为雌激素治疗组。免疫组织化学法观察白细胞介素1在各组大鼠拔牙后牙槽骨改建过程中的表达变化。 结果与结论：卵巢切除后,骨质疏松模型组大鼠的骨小梁薄而少,骨小梁间距变宽,颌骨骨强度下降。应用雌激素治疗后,发现雌激素治疗组白细胞介素1的阳性表达较骨质疏松组减少。提示3月龄SD雌性大鼠去卵巢8周后可发生骨质疏松,雌激素治疗对骨质疏松大鼠拔牙创骨愈合牙槽骨中白细胞介素1表达有明显的抑制作用。