Variation of trabecular microarchitectural parameters in cranial, caudal and mid-vertebral regions of the ovine L3 vertebra

The lumbar vertebrae are major load-bearing structures within the spinal column. The current understanding of the microstructure of these bodies and their full role in load-bearing is incomplete. There is a need to develop our understanding of these issues to improve fracture prediction in musculoskeletal diseases such as osteoporosis. The lumbar vertebrae consist primarily of trabecular bone enclosed in a thin cortical shell, but little is known about how microstructural parameters vary within these structures, particularly in relation to the trabecular compartment. The specific aim of this study was to use micro-computed tomography to characterize the trabecular microarchitecture of the ovine L3 vertebra in cranial, mid-vertebra and caudal regions. The L3 vertebra was obtained from skeletally mature ewes ( n  = 18) more than 4 years old. Three-dimensional reconstructions of three pre-defined regions were obtained and microarchitectural parameters were calculated. Whereas there was no difference in bone volume fraction or structural model index between regions, trabecular number, thickness, spacing, connectivity density, degree of anisotropy and bone mineral density all displayed significant regional variations. The observed differences were consistent with the biomechanical hypothesis that in vivo loads are distributed differently at the endplates compared with the mid-vertebra. Thus, a more integrative approach combining biomechanical theory and anatomical features may improve fracture risk assessment in the future.     

骨质疏松性骨折愈合中骨改建的动态参数及骨密度变化

背景：当骨质疏松骨强度下降时,遭受轻微创伤或其他各种风险因素均易发生骨折。 目的：观察骨质疏松性骨折愈合过程中骨小梁组织学变化,骨密度及骨矿化沉积率的改变。 方法：SD大鼠随机分为骨质疏松组与对照组,骨质疏松组大鼠切除双侧卵巢,术后3个月,建立骨折模型。骨折后4,8,12,16 周,荧光显微镜下观察骨改建的动态参数,双能X线骨密度仪下测定骨痂组织的骨密度;骨折后1,2,4,6,8,12,16 周,应用自动图像系统测量骨组织形态。 结果与结论：骨质疏松组大鼠成熟小梁骨占骨痂面积比对照组小,且小梁骨厚度变薄、小梁骨间距较宽,骨质疏松组骨小梁表面荧光标记百分比及骨痂组织骨密度低于对照组;而骨矿化沉积率高于后者对照组。说明在骨质疏松性骨折愈合过程中,骨痂组织的组织学的异常改变导致骨折愈合质量的降低。     

Does subchondral bone of the equine proximal phalanx adapt to race training?

Sagittal fractures of the first phalanx are a common, potentially catastrophic injury in racehorses. These fractures are often linked to an acute, one time, biomechanical event; however, recent evidence implies that chronic exposure to stress can lead to the accumulation of bony changes that affect the structural integrity of the bone and increase the likelihood of fracture. The aim of the study was to compare variations of two common metrics of bone adaptation – subchondral bone density and thickness across the proximal articular surface of the first phalanx in Thoroughbred horses that (1) raced but never experienced a first phalanx fracture (Raced Control); (2) raced and had experienced fracture of the contralateral first phalanx (Contralateral to Fracture); (3) had never raced or experienced a first phalanx fracture (Unraced Control). A total of 22 first phalangeal bones were sampled post‐mortem and imaged using micro‐computed tomography calibrated for mineral density measures. Measurements of volumetric subchondral bone mineral density and thickness were taken from images at five sites from medial to lateral, in three coronal planes (25, 50 and 75% dorsal‐palmar). At each of the 15 sites, measurements were repeated and averaged across 10 adjacent micro‐computed tomography slices of bone, spanning 0.75 mm. The magnitude and variance of these measurements were compared between sites and between cohorts with non‐parametric statistical tests. Across the proximal osteochondral surface of the first phalanx, the pattern of subchondral bone volumetric bone mineral density and thickness varied with each coronal section studied. The subchondral bone thickness was greater for the central and dorsal coronal sections, compared with the palmar section. For the race‐fit groups (Raced Control and Contralateral to Fracture), the highest volumetric bone mineral density was in the central sagittal groove. The volumetric bone mineral density was significantly greater in the sagittal groove in the central coronal section in the raced than the unraced group. The Contralateral to Fracture group demonstrated significantly greater variance of volumetric bone mineral density compared with the Raced Control and Unraced Control (P < 0.0001), with no difference in variance noted between the Raced Control and Unraced Control groups. There was a small (R rank = 0.3) but significant correlation between subchondral bone volumetric bone mineral density and thickness in the Contralateral to Fracture group (P = 0.005). The findings demonstrate that differences exist in subchondral bone volumetric bone mineral density and thickness across the proximal osteochondral surface of the equine first phalanx in horses with different training histories. The findings also demonstrate that the subchondral bone of the sagittal groove of the equine first phalanx adapts to race‐training in the race‐fit groups (Raced Control and Contralateral to Fracture) with an increase in volumetric bone mineral density relative to unraced controls. Within the race‐trained groups, the Contralateral to Fracture bones had a greater variance of volumetric bone mineral density, suggesting that stress‐induced bone adaptation had become more erratic, potentially contributing to the aetiology of sagittal fractures of the first phalanx in the Thoroughbred racehorse.     

Comparative study of iliac crest and proximal femur histomorphometry in normal patients.

The relation between the bone histomorphometric profile of the iliac crest and regions of the proximal femur was investigated. In the proximal femur four blocks were selected, representing the subchondral principal compressive (SPC) and tensile (SPT) regions, the zone near the medial cortex in the principal compressive region (MPC), and the zone medial to the greater trochanter (MGT). Undecalcified tissue sections stained by the von Kossa silver method and counterstained with haematoxylin and eosin were used for quantitation. The SPT region was most representative of the iliac bone profile, in particular the structural parameters of mineralised bone, trabecular thickness, and trabecular spacing and resorption surface. Most parameters in the regions studied showed inconsistent and variable results when compared with those of the iliac crest. There was only a weak association, therefore, between the histomorphometric parameters of the iliac crest and the proximal femur despite the appeal of the use of the iliac biopsy specimen as a simple clinical test.     

椎体骨微结构参数与椎弓根螺钉固定强度的相关性

目的 测量不同骨密度（bone mineral density, BMD）条件下椎体松质骨显微结构参数,并与椎弓根螺钉拔出力作相关性分析,以了解与螺钉稳定性相关的骨显微结构参数,进一步明确螺钉松动的原因。方法 采用新鲜尸体脊柱标本,根据BMD检测结果,按临床诊断标准分为骨质正常、骨量减少、骨质疏松和重度骨质疏松4个水平。然后植入椎弓根螺钉,进行螺钉轴向拔出实验,测定最大拔出力（maximum pullout strength, MPS）。收集螺钉拔出实验后椎体标本,在椎体中央部钻取松质骨柱状样本,对样本进行显微CT扫描,获取椎体松质骨显微结构参数,并进行各项指标的不同BMD水平间的比较分析,在了解这些指标随骨质疏松程度加重的变化规律的基础上,再对骨显微结构参数与所对应的螺钉MPS开展相关性分析。结果BMD水平从正常下降到重度疏松程度,MPS随之显著性下降。随BMD水平的依梯次下降,即骨质疏松程度进行性加重,椎体松质骨显微结构参数发生相应明显变化,存在BMD水平间的显著性差异。广泛的相关性存在于BMD、显微CT参数和螺钉MPS指标之间。其中,螺钉MPS与显微CT扫描所得的骨体积分数（BV/TV）、骨小梁厚度（Tb.Th）和小梁间隙（Tb.Sp）呈高度相关性。结论 随BMD下降,骨组织会同时发生质的退变;螺钉MPS与部分骨显微结构参数高度相关。     

尼尔雌醇对去卵巢大鼠胫骨骨重建的影响

目的　探讨尼尔雌醇防治绝经后骨质疏松 (PMO)的作用机制。方法　雌性Wistar大鼠30只 ,随机分成假手术组、去卵巢组和尼尔雌醇治疗 (N)组。假手术组进行假手术 ,其余 2组切除卵巢制备PMO模型 ,N组使用尼尔雌醇治疗 3个月。各组动物处死后 ,取一侧胫骨提取总RNA ,逆转录 聚合酶链反应 (RT PCR)检测白细胞介素 (IL 6 )mRNA表达情况。另一侧用骨形态计量学方法研究去卵巢大鼠胫骨干骺端对尼尔雌醇的治疗反应 ,包括静力学参数 :(1)骨小梁体积 (TBV)占全部骨组织体积 (TTV)的百分比 (TBV/TTV) ;(2 )骨小梁表面与其体积之比 (S/V) ;(3)TBV占海绵骨 (SBV)体积的百分比 (TBV/SBV) ;(4 )平均骨小梁板厚度 (MTPT) ;(5 )平均骨小梁板密度 (MTPD) ;(6 )平均骨小梁板间隙 (MTPS) ;(7)平均骨皮质厚度 (MCW)。动力学参数 :(1)骨小梁类骨质表面占骨小梁表面的百分比 (TOS) ;(2 )平均类骨质宽度 (MOSW) ;(3)四环素单标记线占骨小梁表面的百分比 [Sfract(s) ];(4 )四环素双标记线占骨小梁表面的百分比 [Sfract(d) ];(5 )四环素单标记线的 1/ 2和双标记线之和占骨小梁表面的百分比 [Sfract(s/ 2 d) ];(6 )四环素双标记线间的平均距离 (DDL) ;(7)矿化沉积率 (MiAR) ;(8)矿化延迟时间 (MLT) ;(9)组织水平的骨形成率 (Svf) ;     

A review of magnetic resonance (MR) imaging of trabecular bone micro-architecture: contribution to the prediction of biomechanical properties and fracture prevalence.

Bone mineral density and three-dimensional trabecular structure play a significant role in predicting bone strength and biomechanical properties. MR is a non-invasive technique for determining trabecular architecture both in vivo and in vitro. In this paper we review the use of magnetic resonance imaging to obtain high resolution images of trabecular bone structure and quantify the three-dimensional architecture of the trabecular bone network. Studies assessing the anisotropy of the trabecular architecture in human cadaveric specimens from the distal and proximal femur, and the thoracic and lumbar vertebrae, are reviewed. The contributions of the MR derived measures of 3D trabecular bone structure to the biomechanical strength of the specimen are presented. In vivo, the relationship between the high resolution MR derived trabecular bone structure parameters in the distal radius and calcaneus in patients with hip fractures, are compared to age matched normal controls. MR derived measures are compared to measures of trabecular bone mineral density (BMD) in the hip using dual X-ray absorptiometry (DXA).     

Estimating structural properties of trabecular bone from gray-level low-resolution images

In this paper the relationship between three-dimensional histomorphometric parameters derived from microCT and MRI images of distal radius trabecular bone samples is studied. microFE analysis of the trabecular samples is performed and Young's modulus for cranio-caudal direction is calculated. Most of the MRI and microCT parameters correlate significantly with, respectively, MRI and microCT estimates of bone volume fraction. For some of the parameters strong correlation between microCT and MRI results is also observed. However, in these cases there simultaneously exists correlation between: microCT parameter and microCT bone volume fraction; microCT and MRI bone volume fraction; MRI bone volume fraction and MRI parameter. It is found that, comparing to bone volume fraction, histomorphometric information derived from binarized MRI images does not improve estimation of the Young's modulus of trabecular bone samples (calculated for "gold standard" microCT data). Thus a novel method of "optimal paths" analysis of gray-level MRI images is introduced. "Optimal paths" parameters improve estimation of the Young's modulus of trabecular bone samples. They also provide surrogate, gray-level image-based measure of trabecular thickness.     

Morphological,biochemical and mechanical properties of articular cartilage and subchondral bone in rat tibial plateau are age related

The purpose of this study was to investigate age‐related changes in the morphological, biochemical and mechanical properties of articular cartilage (AC) and subchondral bone in the rat tibial plateau. Female Wistar rats were grouped according to age (1, 3, 5, 7, 9, 11, 13, 15, 16 and 17 months, with 10 rats in each group). The ultrastructures, surface topographies, and biochemical and mechanical properties of the AC and subchondral bone in the knee joints of the rats were determined through X‐ray micro‐tomography, histology, immunohistochemistry, scanning electron microscopy (SEM), atomic force microscopy and nanoindentation. We found that cartilage thickness decreased with age. This decrease was accompanied by functional condensation of the underlying subchondral bone. Increased thickness and bone mineral density and decreased porosity were observed in the subchondral plate (SP). Growth decreased collagen II expression in the tibial cartilage. The arrangement of trabeculae in the subchondral trabecular bone became disordered. The thickness and strength of the fibers decreased with age, as detected by SEM. The SP and trabeculae in the tibial plateau increased in roughness in the first phase (1–9 months of age), and then were constant in the second phase (11–17 months of age). Meanwhile, the roughness of the AC changed significantly in the first phase (1–9 months of age), but the changes were independent of age thereafter. This study gives a comprehensive insight into the growth‐related structural, biochemical and mechanical changes in the AC and subchondral bone. The results presented herein may contribute to a new understanding of the pathogenesis of age‐related bone diseases.     

Enhancement of subchondral bone quality by alendronate administration for the reduction of cartilage degeneration in the early phase of experimental osteoarthritis

To evaluate the effects of alendronate (ALN) on the subchondral bone quality and cartilage degeneration in the early phase of experimental model of osteoarthritis after anterior cruciate ligament transaction (ACLT). Thirty male adult healthy Japanese white rabbits after right ACLT or sham operation were divided into three groups (n = 10 per group): Sham; ACLT + ALN [after ACLT, the rabbits were treated with ALN daily starting from 4 days after surgery (10 μg/kg/d subcutaneously)]; and ACLT + NS group (after ACLT, the rabbits were injected saline as a placebo). At 60 days postsurgery, specimens from the affected knees were harvested. Histological analysis (HE and Safranin-O staining) as well as Mankin score were carried out to assess the cartilage degradation. BMP-2 and MMP-13 immunohistochemistry were also performed to demonstrate the alterations of cartilage molecular metabolism. Subchondral bone quality was evaluated by bone mineral density (BMD) and microstructure histomorphometry assay. For bone mineral density evaluation, 1/4 distal femurs, medial and lateral regions of femoral condylus were scanned with dual X-ray absorptiometry to assess the subchondral bone mass. Giemsa, von Kossa stain, and fluorescence technique for undecalcified bone section were carried out to examine the morphometry of the subchondral trabecular bone and subchondral plate. Histological and Mankin score analyses displayed that ALN treatment markedly reduced cartilage lesions and delayed the cartilage degeneration in OA joints. Immunohistochemistry assay further indicated that this cartilage-protective role of ALN was associated with elevating BMP-2 while inhibiting MMP-13 expression. BMD assessment demonstrated that ALN treatment significantly suppressed subchondral bone resorption. The results from histomorphometry assay of subchondral bone revealed that ALN treatment markedly increased the percent trabecular area (BV/TV), trabecular thickness (Tb.Th), and trabecular number (Tb.N). Moreover, both thickness and the porosity of the subchondral plate in ACLT + ALN group presented significantly higher than that in ACLT + NS group, while no significant difference was found between ACLT + ALN and Sham group. ALN plays an important role in cartilage protection in OA joints that is associated with the improvement of subchondral bone quality through reduction of subchondral bone resorption. ALN could be potentially used as a disease-modifying strategy to limit the progression of OA.     

Effects of Loading Orientation on the Morphology of the Predicted Yielded Regions in Trabecular Bone

While the effects of bone mineral density and architecture in osteoporotic bone have been studied extensively, the micromechanics of yielding and failure have received less attention. However, understanding architectural features associated with failure should provide insight into assessing bone quality. In this study, microstructural finite element models were used to compute regions of tissue level yielding in ten bovine tibial trabecular bone samples. The morphology, number, and mean volume of the yielded regions were quantified for four apparent strains under two loading conditions. For on-axis loading, the mean aspect ratio of the tissue that yielded due to compressive strain increased with increasing apparent strain, expanding along the principal trabecular orientation. This suggests that tissue level yielding progresses along vertical trabeculae when a specimen is loaded on-axis. The number, but not the volume, of the regions yielded due to tensile strain increased with increasing applied load, consistent with relaxation and redistribution of stresses around the yielded regions. When the specimens were compressed perpendicular to the principal axis, the aspect ratio of the yielded regions was close to one, while the number, mean volume, and mean thickness of the yielded regions increased. This indicates that localized high strains consistent with bending rather than axial deformation of struts occur at the tissue level. Overall, the results provide new insight into trabecular bone failure, which is relevant to assessing diagnostic tests for fracture risk or evaluating osteoporosis treatments.     

金属植入物固定与修复新鲜不稳定型桡骨远端骨折合并腕舟状骨骨折：半年随访

BACKGROUND: Healing time and plaster used in fixed position and fixed time are different between distal radius fractures and scaphoid fracture. When both fractures occur simultaneously, you cannot choose a fixed position and determine a fixed time. One-stage internal fixation for the distal radial fractures and scaphoid fractures simultaneously can obtain a good function.  OBJECTIVE: To retrospectively analyze the effects of titanium locking compression plate and Herbert screw fixation for fresh unstable distal radial fractures with scaphoid fracture. METHODS: A total of 12 patients with fresh unstable distal radial fractures combined with scaphoid fracture were treated in the Shanxi Dayi Hospital from November 2011 to June 2014. All cases received open reduction and locking compression plate fixation of the distal radius, open reduction of scaphoid fracture or percutaneous Herbert screw fixation. Fracture healing was observed during follow-up. At 6 months after treatment, wrist joint function was evaluated with modified McBride score. Range of motion of palmar flexion, dorsiflexion, ulnar deviation, radial deviation, pronation and supination and grip strength were measured. The distal radial shortening (difference in height of styloid process of radius and ulna), and angles of ulnar deviation and palmar tilt were measured with X-ray films. The data of healthy side and affected side were compared. RESULTS AND CONCLUSION: (1) 12 cases were followed up for 6-24 months. (2) The distal radius and scaphoid fractures healed. The healing time of distal radius was 6-12 weeks, with an average of seven weeks. Healing time of scaphoid fracture was 3-6 months, with an average of 4.2 months. (3) Wrist score was evaluated using modified McBride scoring criteria at 6 months after treatment. There were excellent in 5 cases, good in 6 cases, and average in 1 case, with the excellent and good rate of 92%. (4) No significant difference in range of motion of palmar flexion, dorsiflexion, ulnar deviation, radial deviation, pronation and supination and grip strength, angles of ulnar deviation and palmar tilt, difference in height of styloid process of radius and ulna and modified McBride score was detected between healthy side and affected side (P > 0.05). (5) The median nerve injury in two patients was recovered within 6 months after postoperative exploration decompression. No complications appeared, such as infection, dorsal muscle tendon irritation symptoms, carpal tunnel syndrome, and internal fixation failure. (6) These findings confirm that fresh unstable distal radial fractures with scaphoid fractures can be treated with open reduction of the distal radius and locking plate fixation, open reduction of scaphoid bone or percutaneous Herbert screw fixation, with reliable fixation, high fracture healing rate, and good wrist function recovery rate; the repair effect is satisfactory.      

Effects of bone ingrowth on the strength and non-invasive assessment of a coralline hydroxyapatite material

The dependence of strength on the amount of bone growth into a hydroxyapatite material made from coral was investigated. Block and granular forms of the material were implanted into cortical and trabecular regions of the skeletons of 16 dogs. The results were examined after 4, 8, 12 and 16 wk, with four dogs in each experimental group. When implanted into cortical bone, the bending strength of the implant material was found to be highly correlated with the amount of pore space which had become occupied by bone (r = 0.92, P less than 0.005 for the block form; r = 0.84, P less than 0.005 for the granular form). Multiple regression analysis showed that six histomorphometric measures of ingrowth accounted for 96% of the variability in bending strength of the block material, and there were no significant differences between block and granular forms of the material. On the other hand, when implanted into trabecular bone, the block form of the material achieved greater compressive strength than the granular form. While both strength and ingrowth increased with time, there were poor correlations between these two variables. Finally, when the material is implanted into trabecular bone, it becomes stronger in compression than the surrounding bone; when implanted in cortical bone, linear modelling suggests that resorption and replacement of the implant would be required to approximate the bending strength of the surrounding bone.     

A computer-assisted method for the study of the trabecular bone of the distal radius on conventional radiographs

The procedure described is based on the acquisition and processing of x-rays of the distal radius obtained under standard conditions. An x-ray was obtained of the forearm together with an aluminum step wedge to automatically normalize the photometric values of the bone with respect to the photometric values of the reference aluminum wedge. Densitometric values for thickness (T) and a coarseness parameter (C) that depends on the trabecular bone pattern are measured on interactively selected rows and regions of interest (ROIs) of the digital image. Twenty-five women were examined and two different measurements were performed. The first measurement considers C in three sites of the radial epiphisis. The trabecular bone coarseness appears to increase from the distal to the very-very distal site and the value of C in the very distal site, which is located 1 cm distally to the distal one tenth of the radius, seems to be related to the pathological variations more than the value of C in the other sites. The second measurement is the C/T ratio of eight ROIs of 15 patients: five healthy and 10 osteoporotic women. This ratio is significantly different for the two groups in all the eight ROIs and the variations are particularly significant at 6 to 12 mm from the subchondral line.     

局部注射辛伐他汀对骨质疏松大鼠股骨髁骨小梁的改建效应

背景：局部注射具有成骨作用的辛伐他汀,可显著增加骨质疏松大鼠股骨颈及股骨髁部的骨密度及力学强度,分析局部注射辛伐他汀对股骨髁骨小梁的影响。 目的：进一步研究骨质疏松大鼠股骨内局部注射辛伐他汀对股骨髁骨小梁的影响。为将辛伐他汀应用于临床骨质疏松局部治疗提供实验基础。 方法：18只雌性SD大鼠双侧卵巢切除后3个月,制备大鼠骨质疏松模型。实验大鼠随机数字表法均分为3组,分别在实验大鼠的右侧股骨髓腔内单次注射辛伐他汀溶液5 mg、10 mg,对照组单纯注射空白载体。分别在注射后1个月处死大鼠并取材。Micro-CT扫描并定量分析骨组织形态变化。 结果与结论：给药后1个月,Micro-CT扫描结果显示,辛伐他汀治疗组的骨微结构参数如骨皮质厚度、骨小梁密度及连接率明显优于对照组。说明疏松骨骼单次注射小剂量辛伐他汀可显著促进股骨髁部骨小梁改建,改善骨骼微结构,可为强化局部、防治骨质疏松骨折的新选择进一步提供实验基础。     

On the Failure Initiation in the Proximal Human Femur Under Simulated Sideways Fall

The limitations of areal bone mineral density measurements for identifying at-risk individuals have led to the development of alternative screening methods for hip fracture risk including the use of geometrical measurements from the proximal femur and subject specific finite element analysis (FEA) for predicting femoral strength, based on quantitative CT data (qCT). However, these methods need more development to gain widespread clinical applications. This study had three aims: To investigate whether proximal femur geometrical parameters correlate with obtained femur peak force during the impact testing; to examine whether or not failure of the proximal femur initiates in the cancellous (trabecular) bone; and finally, to examine whether or not surface fracture initiates in the places where holes perforate the cortex of the proximal femur. We found that cortical thickness around the trochanteric-fossa is significantly correlated to the peak force obtained from simulated sideways falling (R ² = 0.69) more so than femoral neck cortical thickness (R ² = 0.15). Dynamic macro level FE simulations predicted that fracture generally initiates in the cancellous bone compartments. Moreover, our micro level FEA results indicated that surface holes may be involved in primary failure events.     

可注射硫酸钙修复骨质疏松大鼠股骨近端骨小梁的实验研究*

目的探讨可注射硫酸钙植入对骨质疏松大鼠股骨近端骨小梁的影响。方法复制去卵巢大鼠骨质疏松模型,采用穿刺注射技术将可注射硫酸钙植入骨质疏松实验大鼠股骨近端,对侧做自身对照,于术后2、4、8、12周取材,对双侧股骨近端行影像学、组织学观察,骨组织形态计量学及双能x线骨密度测定。结果影像学显示：术后4、8、12周实验侧股骨近端密度明显高于对照侧。骨组织学检查显示：术后4周实验侧硫酸钙降解,出现成骨效应;8周股骨近端穿刺注射区域已为致密、分化不成熟的骨小梁所填充;12周股骨近端骨小梁得到较好修复,为成熟的骨小梁组织所填充;对照侧为典型骨质疏松病理改变。骨组织形态计量学测定显示：术后8和12周实验侧骨小梁面积百分数、骨小梁宽度和骨小梁数量显著高于对照侧,实验侧骨小梁分离度显著小于对照侧。术后2、4、8、12周实验侧股骨近端骨密度较对照侧明显增加。结论可注射硫酸钙能快速有效的修复骨质疏松大鼠股骨近端骨小梁。     

Topographical variations in articular cartilage and subchondral bone of the normal rat knee are age-related

In osteoarthritis animal models the rat knee is one of the most frequently investigated joint. However, it is unknown whether topographical variations in articular cartilage and subchondral bone of the normal rat knee exist and how they are linked or influenced by growth and maturation. Detailed knowledge is needed in order to allow interpretation and facilitate comparability of published osteoarthritis studies. For the first time, the present study maps topographical variations in cartilage thickness, cartilage compressive properties and subchondral bone microarchitecture between the medial and lateral tibial compartment of normal growing rat knees (7 vs. 13 weeks). Thickness and compressive properties (aggregate modulus) of cartilage were determined and the subchondral bone was analyzed by micro-computed tomography. We found that articular cartilage thickness is initially homogenous in both compartments, but then differentiates during growth and maturation resulting in greater cartilage thickness in the medial compartment in the 13-week-old animals. Cartilage compressive properties did not vary between the two sites independently of age. In both age-groups, subchondral plate thickness as well as trabecular bone volume ratio and trabecular thickness were greater in the medial compartment. While a high porosity of subchondral bone plate with a high topographical variation (medial/lateral) could be observed in the 7-week-old animals, the porosity was reduced and was accompanied by a reversion in topographical variation when reaching maturity. Our findings highlight that there is a considerable topographical variation in articular cartilage and subchondral bone within the normal rat knee in relation to the developmental status.     

Integrating micro CT indices,CT imaging and computational modelling to assess the mechanical performance of fluoride treated bone

In this study we evaluate the influence of low-dose fluoride treatment on 23 patient biopsies. Computational finite element (FE) models of each biopsy were subjected to a range of loads including compression, shear and torsion. The modelling framework was validated against three 3D printed models with known material properties subjected to compression till failure using an Instron machine. The primary outcomes from this study were that mechanical strength was not significantly correlated to low-dose (<10 mg/day) of fluoride levels (one-way ANOVA, P-values of 0.78, 0.69 and 0.62 for compression, shear and torsion, respectively). However, when bulk bone material properties were derived from DXA bone mineral density (BMD) from each patient's proximal femur a non-significant linear decline in mechanical strength with increase in fluoride was predicted. When the same material property was used for all bones (to evaluate bone architecture influence) then mechanical strength showed a characteristic concave upwards trend, consistent with the variation of micro CT derived percentage bone volume (BV/TV). The secondary outcomes from this study were that in compression, BV/TV was observed to be a strong surrogate measure for mechanical strength (R² = 0.83), while bone surface density (R² = 0.6), trabecular thickness (R² = 0.5) and intersection surface (R² = 0.6) also explained the variation of mechanical strength well. However, trabecular separation and trabecular number were mildly correlated with mechanical strength (R² of 0.31 and 0.35, respectively). Compression was the loading mode most strongly correlated to micro CT indices. Material properties adapted from the proximal femur reduced the CT index correlations by up to 58% indicating that bulk density from a near proximity is a poor representation of specific localised density. Substituting the 3D micro CT indices with 2D histomorphometric data decreased correlations by at least 33% indicating that structural identification on a plane is not representative of the full 3D architecture necessary for a complete bone strength analysis. The presented computational framework may be used to assess the roles that bone architecture and loading modes play in bone quality, and which micro CT indices are good surrogate measures for mechanical strength.     

Micro CT analysis of the subarticular bone structure in the area of the talar trochlea

Purpose

Certain regions of the talar trochlea are recognized as exhibiting varying cartilage thickness and degrees of subchondral bone mineralization. These changes have been attributed to the long-term loading history. For the current study, we accepted the hypothesis that stress-induced alterations of the joint surface include not only varying degrees of subchondral lamellar mineralization, but also structural changes of the subarticular cancellous bone.

Methods

In order to examine the structure of the subarticular cancellous bone, ten formalin-fixed talar trochleae were analyzed using micro CT. Sixteen measurement zones were defined and then evaluated in five layers each of 1-mm thickness, enabling assessment of the cancellous architecture extending 5 mm below the trochlear surface using numerical and structural parameters.

Results

As with mineralization patterns in the subchondral lamella, large variation was observed regarding bone volume, trabecular quantity, thickness, and spacing, as well as for structure model index and degree of anisotropy, depending on localization. In addition, like previous reports examining mineralization of the subchondral lamella, two distinct groups could be identified as “bicentric” or “monocentric”.

Conclusions

These results show that structural tissue adaptation probably due to loading history is also evident within the subarticular cancellous bone.