人体下颈椎显微骨硬度体外测量的实验研究

目的 探讨人体下颈椎C₃~C₇椎骨显微骨硬度的分布特征及其临床意义。方法 3具新鲜成人尸体标本,分别为62岁男性(标本A)、45岁女性(标本B)、58岁男性(标本C),由河北医科大学解剖学教研室提供。取其下颈椎C₃~C₇段脊柱,剔除附着软组织。每个椎骨分为椎体区和附件区两部分,使用高精慢速锯分别经椎体中部垂直于椎体上下终板、右侧椎弓根长轴、左侧上下关节突长轴切割3 mm厚骨切片各1片, 并用砂纸打磨,15块椎骨共制成45片骨切片。应用维氏显微硬度测量仪测量骨组织切片不同区域皮质骨和松质骨的显微硬度值,每一个区域选取5个有效显微骨硬度值,全体有效值的平均值作为该区域的硬度值。结果 15块椎骨共计获得825个有效显微骨硬度测量值。 C₃~C₇总体骨硬度值为11.10～47.80 HV,其中皮质骨为(26.04±4.84) HV、松质骨为(22.92±4.78) HV。椎体区皮质骨硬度值为(25.46±4.86) HV、松质骨硬度值为(21.10±4.97) HV,附件区皮质骨硬度值为(26.50±4.78) HV、松质骨硬度值为(24.75±3.80) HV,附件区高于椎体区,差异均有统计学意义(t=2.800、4.978, P值均＜0.05)。3具尸体标本各自的下颈椎在不同部位的骨显微硬度值不同,但椎体区的皮质骨与松质骨骨硬度值均低于附件标本的皮质骨与松质骨骨硬度,其中松质骨之间的差异均有统计学意义(t_A=4.316、t_B=2.364、t_C=2.107, P值均＜0.05);而皮质骨中,仅标本B的差异有统计学意义(t=2.498,P＜0.05)。C₃~C₇各椎骨不同部位的硬度值分布规律与总体一致:椎体区的骨硬度值均低于附件区;其中C₃、C₅、C₆、C₇松质骨的骨硬度值差异具有统计学意义(P值均＜0.05)。 附件分区中,上关节突皮质骨骨硬度低于椎弓根、椎板、横突、下关节突皮质骨骨硬度,差异具有统计学意义(F=8.590, P＜0.05);椎体分区中,下终板皮质骨骨硬度高于上终板和外周终板皮质骨骨硬度,差异具有统计学意义(F=16.365, P＜0.05)。结论 下颈椎椎骨不同部位、不同区域的骨显微硬度存在差异,附件区的皮质骨/松质骨骨硬度分别高于椎体区的皮质骨/松质骨骨硬度。该分布规律是人体活动过程中适应应力应变的生理改变,可以为三维有限元分析、3D打印及术前模拟提供数据支持。     

Effect of View,Scan Orientation and Analysis Volume on Digital Tomosynthesis (DTS) Based Textural Analysis of Bone

Digital tomosynthesis (DTS) derived textural parameters of human vertebral cancellous bone have been previously correlated to the finite element (FE) stiffness and 3D microstructure. The objective of this study was to optimize scanning configuration and use of multiple image slices in the analysis, so that FE stiffness prediction using DTS could be maximized. Forty vertebrae (T6, T8, T11, and L3) from ten cadavers (63–90 years) were scanned using microCT to obtain trabecular bone volume fraction (BV/TV) and FE stiffness. The vertebrae were then scanned using DTS anteroposteriorly (AP) and laterally (LM) while aligned axially (0°), transversely (90°) or obliquely (23°) to the superior–inferior axis of the vertebrae. From the serial DTS images, fractal dimension (FD), mean intercept length (MIL) and line fraction deviation (LFD) parameters were obtained from a 2D-single mid-stack location and 3D-multi-image stack. The DTS derived textural parameters were then correlated with FE stiffness using linear regression models within each scanning orientation. 3D-multi-image stack models obtained from Transverse-LM scanning orientation (90°) were most explanatory regardless of accounting for the effects of BV/TV. Therefore, DTS scanning perpendicular to the axis of the spine in an LM view is the preferred configuration for prediction of vertebral cancellous bone stiffness.     

The impact of mammalian reproduction on cancellous bone architecture

Pregnancy and lactation make demands on maternal calcium homeostasis which may affect bone strength. Recently, changes in cancellous architecture have been described in iliac crest bone biopsies from normal pregnant women but the rarity of such human material means an animal model is essential. The microanatomy of cancellous bone was compared in uniparous and multiparous rats using undecalcified histological sections of lumbar and caudal vertebrae and also proximal femora. An automated trabecular analysis system (TAS) measured a comprehensive range of structural variables including the trabecular number, connectivity and width. In the first pregnancy cycle an early stimulation of bone formation (which quadrupled at some sites) was indicated by an increase in the skeletal uptake and spacing of double calcein labels and the immediate generation of thicker more numerous and interconnected trabeculae. A 40% increase in cancellous bone volume was observed in the lumbar spine in comparison with age-matched virgin controls. In contrast, a rapid succession of 3 pregnancy cycles (including lactation) culminated in cancellous atrophy of 15% at the same site, with a loss in trabecular number ranging from 20% (caudal vertebra) to 30% (lumbar vertebrae). In comparison, the proximal femur lost 40% of its struts but, nevertheless, uniquely sustained its cancellous bone volume. When lactation was excluded the number of struts lost was halved although trabecular thinning then took place which was sufficient to maintain the previous 15% deficit in bone volume. It was concluded that a single pregnancy strengthens the cancellous component of the maternal skeleton while a quick succession of pregnancies weakens it. Lactation influences the pattern of bone loss but not its amount.     

Sustained swimming increases the mineral content and osteocyte density of salmon vertebral bone

This study addresses the effects of increased mechanical load on the vertebral bone of post-smolt Atlantic salmon by forcing them to swim at controlled speeds. The fish swam continuously in four circular tanks for 9 weeks, two groups at 0.47 body lengths (bl) × s(-1) (non-exercised group) and two groups at 2 bl × s(-1) (exercised group), which is just below the limit for maximum sustained swimming speed in this species. Qualitative data concerning the vertebral structure were obtained from histology and electron microscopy, and quantitative data were based on histomorphometry, high-resolution X-ray micro-computed tomography images and analysis of bone mineral content, while the mechanical properties were tested by compression. Our key findings are that the bone matrix secreted during sustained swimming had significantly higher mineral content and mechanical strength, while no effect was detected on bone in vivo architecture. mRNA levels for two mineralization-related genes bgp and alp were significantly upregulated in the exercised fish, indicating promotion of mineralization. The osteocyte density of the lamellar bone of the amphicoel was also significantly higher in the exercised than non-exercised fish, while the osteocyte density in the cancellous bone was similar in the two groups. The vertebral osteocytes did not form a functional syncytium, which shows that salmon vertebral bone responds to mechanical loading in the absence of an extensive connecting syncytial network of osteocytic cell processes as found in mammals, indicating the existence of a different mechanosensing mechanism. The adaptive response to increased load is thus probably mediated by osteoblasts or bone lining cells, a system in which signal detection and response may be co-located. This study offers new insight into the teleost bone biology, and may have implications for maintaining acceptable welfare for farmed salmon.     

A potential mechanism for allometric trabecular bone scaling in terrestrial mammals

Trabecular bone microstructural parameters, including trabecular thickness, spacing, and number, have been reported to scale with animal size with negative allometry, whereas bone volume fraction is animal size‐invariant in terrestrial mammals. As for the majority of scaling patterns described in animals, its underlying mechanism is unknown. However, it has also been found that osteocyte density is inversely related to animal size, possibly adapted to metabolic rate, which shows a negative relationship as well. In addition, the signalling reach of osteocytes is limited by the extent of the lacuno‐canalicular network, depending on trabecular dimensions and thus also on animal size. Here we propose animal size‐dependent variations in osteocyte density and their signalling influence distance as a potential mechanism for negative allometric trabecular bone scaling in terrestrial mammals. Using an established and tested computational model of bone modelling and remodelling, we run simulations with different osteocyte densities and influence distances mimicking six terrestrial mammals covering a large range of body masses. Simulated trabecular structures revealed negative allometric scaling for trabecular thickness, spacing, and number, constant bone volume fraction, and bone turnover rates inversely related to animal size. These results are in agreement with previous observations supporting our proposal of osteocyte density and influence distance variation as a potential mechanism for negative allometric trabecular bone scaling in terrestrial mammals. The inverse relationship between bone turnover rates and animal size further indicates that trabecular bone scaling may be linked to metabolic rather than mechanical adaptations.     

The ovariectomized ewe model in the evaluation of biomaterials for prosthetic devices in spinal fixation.

The effect of surgical ovariectomy on cancellous bone was investigated by comparing mechanical properties and microarchitectural characteristics of the lumbar vertebrae in ovariectomized and sham-operated ewes. Eighteen mongrel ewes, 4+/-1 years old, were randomly divided into three groups: 6 animals served as a control group (Baseline), 6 were bilaterally ovariectomized (OVX), and the others were used as a sham-operated group (SHAM). OVX and SHAM ewes were euthanized 24 months after surgery; the L5 vertebrae were processed for mechanical and histomorphometric analyses. Maximum load, maximum strength (p<0.0005) and elastic modulus (p <0.005) decreased by about 28% in the OVX group in comparison with the other groups. In the OVX group, vertebral cancellous bone volume, trabecular thickness and trabecular number decreased by about 32% (p<0.0005), 15% (p=0.001) and 20% (p=0.019), respectively. An overall decrease in the bone turnover rate of the OVX group was registered in terms of bone formation rate (p=0.007) and activation frequency (p<0.0005). The variations observed in cancellous bone mechanics and histomorphometry would suggest the development of an osteopenic state in ewe vertebrae at 24 months. Such findings may be useful for future experimental investigations on biomaterials and prosthetic devices to be implanted in the osteopenic spine.     

胸骨柄松质骨结合钛网支撑满足颈椎前路修复植骨需求的可行性

背景：现今临床上常用的自体植骨材料多为髂骨、胫骨、腓骨等部位的松质骨块或骨碎块。采用胸骨柄松质骨作为植骨材料融合稳定颈椎未见报道。 目的：测量国人胸骨柄标本及无明显退变的颈椎X射线侧位片,探讨胸骨柄内松质骨结合钛网植骨在颈椎前路手术中应用的可行性,为自体骨移植开发一个新的植骨材料来源。 方法：测量40具胸骨柄标本的胸骨柄长、胸骨柄最大宽、胸骨柄最小宽、胸骨柄厚、胸骨柄前皮质厚及胸骨柄后皮质厚,计算胸骨柄体积。将胸骨柄长、胸骨柄最大宽、最小宽每边减去4 mm,胸骨柄前、后皮质骨减去1 mm作为胸骨柄内松质骨取骨区(以下简称供区)边界,计算胸骨柄内供区的体积。选择106例无明显退变的中立位颈椎侧位X射线片,测量C_2~3至C₇~T₁椎间隙和C3~C7椎体高度。计算常规颈椎前路术中单间隙、双间隙、三间隙椎间盘切除,1个椎体+2个椎间盘及2个椎体+3个椎间盘切除所需钛网长度和钛网内所需植骨体积。验证供区内松质骨是否满足临床需要。 结果与结论：胸骨柄体积为(17 735.51±    5 231.93) mm³;供区松质骨体积为(8 982.83± 2 437.56) mm³。颈前路术中使用钛网最短和所需植骨量最小为单间隙植骨,所需钛网最长和所需植骨量最大为2个椎体+3个椎间隙切除。颈椎前路常用的任意一种术式中,钛网内所需盛骨体积均明显小于供区体积。提示胸骨柄内松质骨结合钛网支撑可满足大多数颈椎前路融合过程中的植骨需求。与自体髂骨植骨相比,操作更简单方便,不影响患者早期功能锻炼和负重行走。     

Trabecular Microarchitecture of Hominoid Thoracic Vertebrae

Spontaneous vertebral fractures are a common occurrence in modern humans, yet these fractures are not documented in other hominoids. Differences in vertebral bone strength between humans and apes associated with trabecular bone microarchitecture may contribute to differences in fracture incidence. We used microcomputed tomography to examine trabecular bone microarchitecture in the T8 vertebra of extant young adult hominoids. Scaled volumes of interest from the anterior vertebral body were analyzed at a resolution of 46 μm, and bone volume fraction, trabecular thickness, trabecular number, trabecular separation, structure model index, and degree of anisotropy were compared among species. As body mass increased, so did trabecular thickness, but bone volume fraction, structure model index, and degree of anisotropy were independent of body mass. Bone volume fraction was not significantly different between the species. Degree of anisotropy was not significantly different among the species, suggesting similarity of loading patterns in the T8 vertebra due to similar anatomical and postural relationships within each species' spine. Degree of anisotropy was negatively correlated with bone volume fraction (r² = 0.85, P < 0.05) in humans, whereas the apes demonstrated no such relationship. This suggested that less dense human trabecular bone was more preferentially aligned to habitual loading. Furthermore, we theorize that trabeculae in ape thoracic vertebrae would not be expected to become preferentially aligned if bone volume fraction was decreased. The differing relationship between bone volume fraction and degree of anisotropy in humans and apes may cause less dense human bone to be more fragile than less dense ape bone. Anat Rec, 2009. © 2009 Wiley‐Liss, Inc.     

Vergleichende rasterelektronenmikroskopische Knochenuntersuchungen bei primärem und sekundärem Hyperparathyreoidismus

Summary Stereoscopic structures of cancellous bone of human vertebral bodies were studied with a scanning electron microcope at autopsy of 2 cases of primary and 4 of secondary hyperparathyreoidism.One principle finding are enlarged resorbing surfaces all over numerous bone trabeculae.There is a compensatory activity of forming surfaces, which brings about mineralizing fronts and extended active osteoid seams. Active fiber osteoid predominates in cases with secondary (renal). HPT. No morphological differences can be demonstrated on bone trabeculae of dialyzed or non-dialyzed patients.These results are in a certain contrast to SEM findings in rat parietal bone after experimental PTH administration, which showed a striking increase of resting surfaces. These short-term animal experiments, however, are not really comparable to human chronic hyperparathyreoidism.The osteocytes of lamellar compact bone prove to be enlarged in cases of primary and secondary hyperparathyreoidism as compared to specimens of normal compact bone. The difference is slight but is statistically significant. We explain this not as periosteocytic osteolysis but as an effect of the disturbed maturation brought about by defective mineralization of the osteocyte capsules.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft. Herrn Dr. med. Bernhard Karhoff zum 60. Geburtstag.     

人体脊柱胸腰段椎骨显微骨硬度分布特征研究

目的 探讨人体胸腰椎段椎骨显微骨硬度的分布特征及临床应用前景。方法 选取3具新鲜成人尸体标本,取出其T₁₁~L₂椎骨后剔除软组织。将每一个椎骨分为椎体区和附件区,经高精慢速锯切割成若干厚约3 mm的骨组织切片,12块椎骨标本共计产生72个骨组织切片。应用维氏显微硬度测量仪测量骨组织切片不同区域皮质骨和松质骨的显微硬度值,每一个区域选取5个有效显微硬度值,全体有效值的平均值作为该区域的硬度值。结果 12块椎骨共进行660次有效压痕实验并取得显微硬度值。(1)胸腰段椎休总体硬度为11.6 ~48.3 HV,其中皮质骨硬度为13.8~48.3(31.62±5.66) HV,松质骨硬度11.6~44.9 (29.62±5.38) HV;(2) 胸腰段椎体区和附件区皮质骨硬度分别为(29.99 ±5.27)HV和(32.92 ±5.63) HV,松质骨硬度分别为(28.44 ±4.79) HV和(30.81±5.71)HV,附件区均高于椎体区,差异均有统计学意义(t=5.098、2.011, P值均＜0.05);(3)椎体区皮质骨硬度由高到低依次为下终板(33.94±4.31)HV、上终板(29.76±4.35)HV、外周终板(28.13±5.07)HV,下终板皮质的骨硬度高于上终板、外周终板,差异均有统计学意义(P值均＜0.05);(4)附件区皮质骨中,硬度由高到低依次为椎弓根皮质(34.78 ±5.30)HV、上关节突(33.73±5.68)HV、椎板(33.15±5.28)HV、横突(31.69±5.37)HV和下关节突(31.26 ±5.91)HV,其中椎弓根皮质骨硬度与横突和下关节突相比,差异均有统计学意义(P值均＜0.05)。结论 本实验首次应用维氏显微硬度方法对人体胸腰椎段椎骨显微硬度的分布规律进行研究,发现胸腰椎段椎骨附件区皮质骨、松质骨骨硬度分别高于椎体区皮质骨、松质骨骨硬度,胸腰椎段T₁₁~L₂之间、不同标本的胸腰椎段的骨显微硬度存在差异,但分布规律相对一致,是微观结构、力学承载共同作用的结果,符合人体正常生理及负重功能。本研究结果可为3D打印制备具有梯度硬度的人工椎骨提供数据支持。     

Determination of bone volume by osteocyte population

During development and growth, biological tissues and organisms can control their size and mass by regulating cell number (Raff, 1992; Conlon and Raff, 1999). Later in life both cell number and organ mass decrease (Buetow, 1985). We demonstrate that the number density of bone cells buried in the calcified matrix (osteocyte lacunar density) predicts extracellular matrix volume for both cancellous and cortical bone in a broad cross-section of the population (males and females, age range 23-91 years, r(2) = 0.98). Our hypothesis is that bone mass is determined by the control of osteocyte number, and that this is a particular instance of the control of organ size through the social controls on cell survival and death (Raff, 1992; Conlon and Raff, 1999).     

Histomorphometric assessment of Haversian canal and osteocyte lacunae in different-sized osteons in human rib

There is no detailed information available concerning the variations in bone, the Haversian canal, and osteocyte populations in different-sized osteons. In this study a total of 398 secondary osteons were measured in archived rib sections from nine white men (20-25 years old). The sections were stained with basic fuchsin. The parameters included the osteon area (On.Ar), Haversian canal area (HC.Ar) and perimeter (HC.Pm), bone area (B.Ar), and osteocyte lacunar number (Lc.N). From these primary measurements the following indices were deduced: 1) lacunar number per bone area (Lc.N/B.Ar) and per osteon (Lc.N/On); 2) the ratio between Haversian canal perimeter and bone area (HC.Pm/B.Ar); and 3) the fraction of Haversian canal area (HC.Ar/On.Ar) and its complement, the fraction of bone area (B.Ar/On.Ar). The results showed that the osteons varied greatly in size, but very little in the fraction of bone area. Regression analyses showed that HC.Ar, HC.Pm, and Lc.N/On were positively associated with On.Ar (P < 0.001 for all). A significant negative correlation was found between On.Ar and Lc.N/B.Ar (P < 0.05) and HC.Pm/B.Ar (P < 0.0001). HC.Ar and HC.Pm increased significantly with increasing Lc.N/On (both P < 0.0001) rather than Lc.N/B.Ar. Lc.N/B.Ar had a significant positive correlation with HC.Ar/On.Ar (P < 0.05) and HC.Pm/B.Ar (P < 0.01). We conclude that: 1) the size of the osteon is determined by the quantum of bone removed by osteoclasts, 2) the osteon is well designed for molecular exchange, and 3) a well designed osteon may be produced via the regulation of bone apposition by osteocytes during the process of osteon refilling.     

Exercise‐induced metacarpophalangeal joint adaptation in the Thoroughbred racehorse

Repetitive bone injury and development of stress fracture is a common problem in humans and animals. The Thoroughbred racehorse is a model in which adaptive failure and associated development of stress fracture is common. We performed a histologic study of the distal end of the third metacarpal bone in two groups of horses: young Thoroughbreds that were actively racing (n = 10) and a group of non‐athletic horses (n = 8). The purpose of this study was to determine whether development of articular microcracks was associated with specific alterations to subchondral plate osteocytes. Morphometric measurements were made in five regions of the joint surface: lateral condyle, lateral condylar groove, sagittal ridge, medial condylar groove, and medial condyle. The following variables were quantified: hyaline cartilage width; calcified cartilage width; the number of tidemarks; microcrack density at the articular surface; blood vessel density entering articular cartilage; the presence of atypical bone matrix in the subchondral plate; bone volume fraction; and osteocyte density. Adaptation of articular cartilage was similar in both groups of horses. Vascularization of articular cartilage was increased in the group of non‐athletic horses. Microcracks, which typically had an oblique orientation to the joint surface, were co‐localized with blood vessels, and resorption spaces. Microcracking was increased in the condylar grooves of athletic horses compared with the other joint regions and was also increased compared with the condylar groove regions of non‐athletic horses. Coalescence of microcracks also led to development of an intracortical articular condylar stress fracture in some joints and targeted remodeling of affected subchondral plate. The subchondral plate of the condyles in athletic horses was sclerotic, and contained atypically stained bone matrix with increased numbers of osteocytes with atypical morphology. However, osteocyte numbers were not significantly different between groups. We conclude that differences in site‐specific microdamage accumulation and associated targeted remodeling between athletic and non‐athletic horses are much greater than differences in subchondral osteocyte morphology. However, the presence of atypical subchondral bone matrix in athletic horses was associated with extensive osteocyte loss. Although osteocyte mechanotransduction is considered important for functional adaptation, in this model, adaptation is likely regulated by multiple mechanotransduction pathways.     

Trabecular Shear Stresses Predict <Emphasis Type="Italic">In Vivo</Emphasis> Linear Microcrack Density but not Diffuse Damage in Human Vertebral Cancellous Bone

Linear microcracks and diffuse damage (staining over a broad region) are two types of microscopic damage known to occur in vivo in human vertebral trabecular bone. These damage types might be associated with vertebral failure. Using microcomputed tomography and finite element analysis for specimens of cancellous bone, we estimated the stresses in the trabeculae of human vertebral tissue for inferosuperior loading. Microdamage was quantified histologically. The density of in vivo linear microcracks was, but the diffuse damage area was not, related to the estimates of von Mises stress distribution in the tissue. In vivo linear microcrack density increased with increasing coefficient of variation of the trabecular von Mises stress and with increasing average trabecular von Mises stress generated per superoinferior apparent axial stress. Nonlinear increase in linear crack density, similar to the increase of the coefficient of variation of trabecular shear stresses, with decreasing bone stiffness and bone volume fraction suggests that damage may accumulate rather rapidly in diseases associated with low bone density due to the dramatic increase of shear stresses in the tissue. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8719Xx, 8759Ls, 8759Fm, 8710+e     

Intervertebral disc disorganisation and its relationship to age adjusted vertebral body morphometry and vertebral bone architecture

Vertebral deformity, intervertebral disc disorganisation, and change to vertebral bone architecture are morphological features that are associated with low back pain. The purpose of this study was to examine the influence of the morphological disorganisation of the intervertebral disc on vertebral body shape indices and vertebral cancellous bone architecture. Lumbar spines, T12-S1, were collected from 27 cadavers. The motion segments T12-L1, L2-L3 and L4-L5 were selected for the study. There were 8 females aged 35-94 years and 19 males aged 20-90 years. An intervertebral disc grade signifying the severity of disc disorganisation was assigned to each disc using the macroscopic disc grading criteria of Hansson and Roos (Spine, 1981; 6:147-153.). Vertebral shape indices and vertebral body bone histomorphometric analyses were performed on the vertebral bodies. Where appropriate, data were age adjusted and the influence of morphological disc disorganisation on vertebral body deformity and cancellous bone architecture analysed. Increased vertebral body axial area and the ratio of vertebral body axial area to sagittal area were associated with an increase in vertebral deformity and disc disorganisation. This suggests that vertebral deformity that remains clinically silent in the general population is influenced by intervertebral disc disorganisation. Vertebral cancellous bone architecture undergoes change associated with increased disc disorganisation, consistent with increased vertebral deformity. Vertebral bodies adjacent to degenerate discs (Grade 4) showed increased BV/TV and Tb.Th and decreased BS/BV. This shows that disc disorganisation may modulate vertebral cancellous bone architecture such that it protects against age-related bone changes. In addition, vertebral body wedging and concavity are associated with smaller vertebral body size and vertebral body compression is associated with larger vertebral body size and compromised cancellous bone architecture.     

腰椎爆裂骨折椎体松质骨内力学分布特点的有限元研究

目的运用有限元方法模拟腰椎爆裂骨折的过程,观察腰椎在轴向压缩载荷作用下松质骨内的应力分布情况。方法建立正常人体胸腰段(T12~L2)运动节段的三维有限元模型,在T12椎体上表面施加不同等级的压力(0.4、0.6、0.8、1.0、1.2 k N),模拟腰椎爆裂骨折发生时椎体承受的不同等级的轴向压缩载荷。将连接椎体上下终板凹面顶点的连线7等分,在此基础上将L1椎体中的松质骨划分为7个具有统计节点的层面,每个统计层面划分成6个统计区。分别测量L1椎体松质骨内3个层面(第1、4、7层面)18个统计区的平均应力。在同一等级载荷下对3个层面内的平均应力进行单因素方差分析,分析腰椎椎体松质骨内不同载荷作用下的应力分布情况。结果在5个不同等级载荷下,第1、7层松质骨平均应力分别与第4层比较有统计学意义(P0.05),而第1、7层平均应力比较无统计学意义(P0.05)。轴向加载时,相比第1、7层应力,椎体松质骨中间层面(第4层)应力最小。结论腰椎在轴向压缩载荷作用下,椎体松质骨内存在应力集中的现象,接近椎体上下软骨板的松质骨应力较大,而椎体松质骨中间层面应力较小,椎体内应力集中分布在上下软骨板的特点与腰椎爆裂骨折所致终板破裂的生物力学机制相一致,提示腰椎椎体骨结构损伤可能与椎体内应力集中有关。     

Morphologic changes associated with functional adaptation of the navicular bone of horses

Failure of functional adaptation to protect the skeleton from damage is common and is often associated with targeted remodeling of bone microdamage. Horses provide a suitable model for studying loading-related skeletal disease because horses are physically active, their exercise is usually regulated, and adaptive failure of various skeletal sites is common. We performed a histologic study of the navicular bone of three groups of horses: (1) young racing Thoroughbreds (n = 10); (2) young unshod ponies (n = 10); and (3) older horses with navicular syndrome (n = 6). Navicular syndrome is a painful condition that is a common cause of lameness and is associated with extensive remodeling of the navicular bone; a sesamoid bone located within the hoof which articulates with the second and third phalanges dorsally. The following variables were quantified: volumetric bone mineral density; cortical thickness (Ct.Th); bone volume fraction, microcrack surface density; density of osteocytes and empty lacunae; and resorption space density. Birefringence of bone collagen was also determined using circularly polarized light microscopy and disruption of the lacunocanalicular network was examined using confocal microscopy. Remodeling of the navicular bone resulted in formation of transverse secondary osteons orientated in a lateral to medial direction; bone collagen was similarly orientated. In horses with navicular syndrome, remodeling often led to the formation of intracortical cysts and development of multiple tidemarks at the articular surface. These changes were associated with high microcrack surface density, low bone volume fraction, low density of osteocytes, and poor osteocyte connectivity. Empty lacunae were increased in Thoroughbreds. Resorption space density was not increased in horses with navicular syndrome. Taken together, these data suggest that the navicular bone may experience habitual bending across the sagittal plane. Consequences of cumulative cyclic loading in horses with navicular syndrome include arthritic degeneration of adjacent joints and adaptive failure of the navicular bone, with accumulation of microdamage and associated low bone mass, poor osteocyte connectivity, and low osteocyte density, but not formation of greater numbers of resorption spaces.