膝关节原发性骨关节炎软骨和软骨下骨病理改变的定量研究

目的观察膝关节原发性骨关节炎(osteoarthritis,OA)胫骨平台软骨和软骨下骨病理改变特点,对比内、外侧平台软骨和软骨下骨结构参数,探讨钙化层和软骨下骨在OA发病机制中的作用。方法取2009年10月-2011年5月行人工全膝关节置换术治疗的30例30膝原发性OA患者自愿捐赠的新鲜胫骨平台标本进行实验。其中男11例,女19例;年龄55～78岁,平均65.1岁。病程10～25年,平均16.6年;患膝内翻畸形1～23°,平均9.3°。大体观察胫骨平台后在内、外侧中央负重区取材,常规制备脱钙石蜡切片,行HE和番红O/固绿染色,观察关节软骨退变特点,参照Mankin评分标准评分并分期;观察钙化层及软骨下骨病理改变。应用Image Pro Plus 6.0图像分析软件测量软骨和软骨下骨结构参数,包括软骨全层(total articular cartilage,TAC)厚度、钙化层(articular calcified cartilage,ACC)厚度、ACC/TAC比值、软骨下骨板(subchondral bone plate,SCP)厚度以及骨小梁体积分数(trabecular bone volume,BV/TV)。结果大体观察内侧平台软骨退变较外侧严重,内侧平台软骨Mankin评分为(12.4±1.1)分,显著高于外侧平台的(8.3±1.6)分(t=12.173,P=0.000)。根据Mankin评分结果在60个标本中,14个为OA早期,可见软骨浅表层裂隙、潮线复制和软骨下骨增厚;19个为OA中期,可见软骨深层裂隙、多发软骨下骨吸收陷窝和明显增厚的软骨下骨;27个为OA晚期,可见软骨全层缺失、软骨内化骨和"象牙化"软骨下骨。软骨和软骨下骨结构参数测定示:内侧平台TAC厚度显著低于外侧平台,ACC/TAC比值、BV/TV及SCP厚度显著高于外侧平台,差异均有统计学意义(P<0.05)。内、外侧平台ACC厚度比较,差异无统计学意义(P>0.05)。结论钙化层和软骨下骨可能在OA发生与进展中发挥了重要作用。     

膝关节退行性骨关节炎钙化层病理改变研究

[目的]对骨性关节炎软骨钙化层病理结构进行形态学分析,为临床诊治及预防相关疾病提供理论依据.[方法]标本均来源于临床诊断为膝关节退行性骨关节炎患者,共21例,其中,男1例,女20例.股骨髁负重区取材、修剪、固定后,常规制备石蜡切片,番红O/固绿染色,显微镜观察.[结果]本研究收集的标本平均年龄(65.57±7.43)岁;平均身高(155.38±5.32)cm;体均体重(59.95±8.99)kg;平均病程(13.04±9.66)年.番红O/固绿染色示钙化层病理改变主要为潮线复制、漂移,出现多条潮线结构,钙化层结构明显增厚,最厚处为900多微米;钙化层增厚伴血管长入;非钙化软骨及钙化层纤维样改变;潮线间隙增宽;钙化层及深层软骨缺损.[结论]膝关节退行性骨关节炎钙化层形态结构具有特异性的病理改变.     

保留钙化层结构的猪股骨滑车全厚软骨缺损模型建立

目的建立保留钙化层结构的猪股骨滑车全厚软骨缺损模型,为观察组织工程软骨在保留钙化层的膝关节软骨缺损模型中的修复效果提供良好的实验研究平台。方法选取6月龄清洁级贵州小香猪9只,体重40～50 kg,用标准的软骨缺损制作套件在其右后肢股骨滑车切迹旁制备直径6 mm、深0.2～0.5 mm、不伤及钙化层结构的圆柱形全厚软骨缺损模型。造模4周后行3.0T MRI观察,取材后进行大体、体视显微镜观察及固绿-番红O、阿利新蓝、天狼星红组织学染色观察缺损处软骨修复情况。结果造模后实验动物均存活,术后切口无感染,无髌骨脱位;术后即可下地行走并部分负重,1周后均能自由活动,无跛行。造模后4周,MRI检查可见滑车处有明显连续信号中断,异常信号深及软骨下骨,缺损周边深层未见明显信号异常。标本大体观察示缺损底部有少量填充物、出血点,与周围正常软骨界限清楚。体式显微镜观察示钙化层基本完整,缺损局部软骨下骨板有塌陷。普通显微镜下,固绿-番红O及阿利新蓝染色示缺损处无软骨细胞及染料着色;偏光显微镜下,天狼星红染色示缺损底部被连续、强折光性的纤维组织少量填充。结论通过该造模方法制作的不伤及钙化层结构的猪股骨滑车全厚软骨缺损模型,可用于骨关节炎早期软骨病变修复的研究及猪软骨钙化层结构作用研究的动物模型。     

关节软骨钙化层相关研究进展

关节软骨钙化层(calcified cartilage zone, CCZ)是软骨组织中一层重要的界面结构,对骨软骨组织生理功能的发挥有着重要意义。相关基础研究及临床研究表明钙化层结构有利于骨关节炎的防治以及软骨组织的再生修复,本文对钙化层的理化性质,及在防治骨关节炎和软骨修复方面的研究进展作一综述。     

关节软骨钙化层研究进展

目的综述关节软骨钙化层的结构和功能及其在骨关节炎(osteoarthritis,OA)发病机制中的作用。方法广泛查阅近年来关于钙化层研究的文献,对钙化层的结构、成分、生物力学和生物化学功能进行总结分析。结果钙化层有特殊的结构和材料特性,并且具备半透膜的性质,钙化层软骨细胞保留部分生长板细胞特性,在维持正常软骨功能和OA发生、发展过程中起重要作用。因此重建关节软骨钙化层已成为近年来兴起的界面组织工程领域研究热点。结论对软骨钙化层的研究需要进一步深入,这在OA治疗和组织工程骨-软骨复合体制备方面都具有重要意义。     

早期跑台运动对SD大鼠股骨内髁软骨缺损修复的影响

[目的]了解SD大鼠膝关节软骨急性缺损后早期高强度跑台运动对软骨修复的影响。[方法]将24只雄性Sprague-Dawley(SD)大鼠随机分为实验组(A组,n=12)与对照组(B组,n=12),两组大鼠均在双侧股骨内髁制造直径1.6 mm全层关节软骨缺损。建模后两组大鼠分笼饲养,自由活动,A组大鼠每天进行一次定时定量的小动物跑台训练,B组不施加运动干预。建模后2、6、10、14周时两组各随机处死3只大鼠,分别进行实验部位的大体观察和HE染色;然后进行番红O-固绿染色,并采用Image-pro plus 6.0图像分析软件测定单位面积番红O-固绿染色的平均光密度值,用以显示糖氨多糖(glycosaminoglycan,GAG)的含量;参照软骨缺损修复的改良Pineda半定量评分法进行评分。[结果]术后2周时,实验组与对照组大体观察实验部位仍存在缺损凹陷;术后6周时,两组缺损处凹陷已基本填平,表面较光滑,色泽较均匀,术后14周时,两组缺损处已与周围正常软骨无明显区别。术后2周时,HE染色两组均可见缺损区凹陷,有少量肉芽组织填充,间质内毛细血管及炎细胞浸润,少量纤维细胞、肌纤维母细胞增生,番红O-固绿无异染性着色;术后6周时,缺损区内炎症明显减轻,底部可见骨小梁,表层有成纤维细胞覆盖,可见少量岛类软骨细胞生长,修复组织和周边软骨组织之间有裂隙或不连续,缺损边缘的组织细胞少,纤维细胞及肌纤维母细胞明显增生,少量纤维软骨形成,番红O-固绿染色见缺损修复区组织染色明显减少;术后10周时,修复组织与周边软骨组织整合程度增加,主要由透明变形的纤维软骨及类透明软骨细胞填满并延伸到两侧关节软骨面,底部及边缘可见骨组织及软骨增生,番红O-固绿染色见修复组织内染色轻度减少,与正常软骨染色区别不明显;术后14周时,表面主要为纤维软骨细胞或类透明软骨细胞覆盖,底部及边缘软骨增生较前增加,但镜下形态与正常软骨组织仍有区别,关节软骨下骨质增生、硬化,增生骨质内可见局限性软骨灶,番红O-固绿染色见修复组织染色较淡,接近正常软骨染色。HE染色及番红O-固绿染色显示缺损处修复组织实验组较对照组修复缓慢,实验组与对照组2周时组织学评分无统计学意义(P>0.05),6、10、14周时两组组织学评分有统计学意义(P<0.01)。番红O-固绿染色平均光密度值6周、10周、14周时实验组低于对照组,有统计学意义,其变化趋势与组织学评分结果一致。[结论]SD大鼠股骨内髁关节软骨全层缺损后,早期高强度跑台运动不利于关节软骨的修复,提示对于关节软骨损伤的患者应避免早期承受过度运动负荷。     

膝关节原发性骨关节炎软骨-软骨下骨复合单元改变的实验研究

[目的]观察膝关节原发性骨关节炎(osteoarthritis,OA)胫骨平台软骨和软骨下骨病理改变特点,评价不同OA期别的骨形态计量学,探讨软骨和软骨下骨在OA发病机制中的相互作用。[方法]取人工全膝关节置换术后的膝原发性OA患者(n=40)自愿捐赠的新鲜胫骨平台标本。大体观察后在胫骨平台内、外侧中央负重区取软骨-软骨下骨复合体并切割等分为A、B两组。A组行番红O/固绿染色,参照Mankin评分标准评分并分1⁴期,观察软骨及软骨下骨病理改变。B组用Mirco-CT扫描测量骨形态计量学参数。[结果]根据Mankin评分,Ⅰ期OA可见软骨浅表层纤维化、潮线复制,Ⅱ期OA可见软骨磨损腐蚀、微骨折形成、血管侵入钙化软骨层,Ⅲ期OA可见多发性裂隙深达软骨下骨、软骨内囊肿、血管越过潮线生长、明显增厚的软骨下骨,Ⅳ期OA可见软骨全层缺失、软骨内化骨、软骨下骨暴露。随OA发展的期别增高,骨矿化密度(bone mineral density,BMD)、骨体积分数(bone volume fraction,BV/TV)、组织矿化密度(tissue mineralized density,TMD)、骨小梁数目(trabecula number,Tb.N)、骨小梁厚度(trabecular thickness,Tb.Th)呈增长趋势,骨小梁间隔(trabecular spacing,Tb.Sp)及结构模型指数(structure model index,SMI)呈下降趋势,且OA各期之间有显著统计学差异(P<0.05)。评价软骨退变的Makin评分与BMD、BVF、Tb.Th呈显著正相关(P<0.001),与SMI呈显著负相关(P<0.001)。[结论]软骨和软骨下骨构成结构和功能上的复合单元,在OA进展中相互影响。异常力学载荷引发骨重塑,微裂隙和血管等连接通道的存在提示软骨和软骨下骨间存在物质传递和分子交流。软骨下骨的特异性改变和软骨退变密切相关。     

实验性骨关节炎中关节软骨钙化层厚度测定及其意义

作者借助髋关节骨关节炎（ＯＡ）实验动物模型、观察到：（１）关节软骨钙化层在负重区分布最厚，非负重区最薄。（２）ＯＡ严重度和钙化层厚度呈正相关，和软骨非钙化软骨厚度呈负相关。（３）ＯＡ病理发展过程中具有非钙化软骨层变薄，钙化软骨层增厚，潮线前移等特征。该结果为分析ＯＡ病因及病理机制提供直接依据。     

骨关节炎中关节软骨和周围骨的变化

骨关节炎(OA)是最常见的关节炎,同时也是造成中老年人伤残的重要原因。曾经一度认为关节软骨的改变是骨关节炎主要的病变,但现在普遍认为,所有关节结构包括软骨钙化区、软骨下骨、骨小梁、关节囊等都会受到影响。然而骨与软骨所起到的作用、之间的关系如何还不明确。本文就骨关节炎中关节软骨和周围骨的变化作一综述。     

激素性骨坏死关节软骨下皮质骨病理改变的实验研究

[目的]观察激素性骨坏死关节塌陷早期软骨下皮质骨的病理形态改变,分析关节塌陷的原因.[方法]将新西兰白兔分为两组,A组复制激素增强的Shwanzman反应骨坏死模型,B组为空白对照组.停药后10周获取肱骨头标本,分别制备脱钙和不脱钙切片,脱钙标本HE染色,观察软骨下皮质骨改变,哈佛管计数.不脱钙标本进行荧光观察,比较软骨下皮质骨形态、结构;扫描电镜观察,比较软骨下微循环改变、软骨下方骨组织形态、结构改变.[结果]A组标本出现坏死改变.软骨下方骨组织内哈佛管减少消失,即软骨下皮质骨及由其构成的球拱、桥拱结构破坏,支撑软骨层的骨组织呈松质骨改变.有部分肱骨头出现关节塌陷早期改变.软骨下微血管内广泛存在红细胞淤滞、填塞现象.B组软骨下方骨组织具有较丰富的哈佛管,为皮质骨.完整且连续的皮质骨支撑关节软骨,同时构成球拱、桥拱结构.软骨下微血管内无红细胞淤滞、填塞现象.[结论]关节软骨下皮质骨缺失是关节发生塌陷的原因.软骨下微循环障碍是其重要原因.     

The ultrastructure and biomechanical significance of the tidemark of articular cartilage.

Thirty specimens of human articular cartilage obtained at surgery were examined by scanning electron microscopy to determine the ultrastructure of the tidemark, the junction of the non-calcified and calcified portions of mature articular cartilage. Three distinct variations of the collagen framework of the tidemark were observed: (1) A band of randomly oriented compacted fibrils that appeared to be continuous with those of the non-calcified and calcified zones. (2) A band of flattened fibrils paralleling the undulating surface of the calcified cartilage. (3) A band of perpendicularly oriented fibrils having a distinct continuous transition between the non-calcified and calcified zones, the amount of calcified material applied about the fibrils rapidly increasing as the fibrils entered the calcified zone. The tidemark may serve to provide a tethering mechanism for the relatively flexible and perpendicularly oriented collagen fibrils of the deepest portion of the non-calcified articular cartilage and may prevent them from being sheared at their point of anchorage to the calcified zone. The undulating pattern of the tidemark affords a strong geometric pattern in providing resistance to the shearing action of articulation. Small gaps present in the tidemark may provide pathways for the passage of nutrients into the deep non-calcified zone of articular cartilage from the subchondral bone.     

The cartilage-bone interface

In the knee joint, the purpose of the cartilage-bone interface is to maintain structural integrity of the osteochondral unit during walking, kneeling, pivoting, and jumping--during which tensile, compressive, and shear forces are transmitted from the viscoelastic articular cartilage layer to the much stiffer mineralized end of the long bone. Mature articular cartilage is integrated with subchondral bone through a approximately 20 to approximately 250 microm thick layer of calcified cartilage. Inside the calcified cartilage layer, perpendicular chondrocyte-derived collagen type II fibers become structurally cemented to collagen type I osteoid deposited by osteoblasts. The mature mineralization front is delineated by a thin approximately 5 microm undulating tidemark structure that forms at the base of articular cartilage. Growth plate cartilage is anchored to epiphyseal bone, sometimes via a thin layer of calcified cartilage and tidemark, while the hypertrophic edge does not form a tidemark and undergoes continual vascular invasion and endochondral ossification (EO) until skeletal maturity upon which the growth plates are fully resorbed and replaced by bone. In this review, the formation of the cartilage-bone interface during skeletal development and cartilage repair, and its structure and composition are presented. Animal models and human anatomical studies show that the tidemark is a dynamic structure that forms within a purely collagen type II-positive and collagen type I-negative hyaline cartilage matrix. Cartilage repair strategies that elicit fibrocartilage, a mixture of collagen type I and type II, are predicted to show little tidemark/calcified cartilage regeneration and to develop a less stable repair tissue-bone interface. The tidemark can be regenerated through a bone marrow-driven growth process of EO near the articular surface.     

The normal human chondro-osseous junctional region: evidence for contact of uncalcified cartilage with subchondral bone and marrow spaces

Background  

The chondro-osseous junctional region of diarthrodial joints is peculiarly complex and may be considered to consist of the deepest layer of non-calcified cartilage, the tidemark, the layer of calcified cartilage, a thin cement line (between the calcified cartilage and the subchondral bone) and the subchondral bone. A detailed knowledge of the structure, function and pathophysiology of the normal chondro-osseous junction is essential for an understanding of the pathogenesis of osteoarthrosis.     

Lead accumulation in tidemark of articular cartilage

OBJECTIVE: Determination of the spatial distribution of the toxic element lead (Pb) and other trace elements in normal articular cartilage and subchondral bone from adult humans with no history of work-related exposure to Pb. METHODS: Four macroscopically normal femoral heads and three patellas were harvested from randomly selected forensic autopsies. All subjects died of acute illnesses, had no history of work-related exposure to Pb and had no metabolic bone disease. The elemental distribution of lead (Pb) together with zinc (Zn), strontium (Sr) and calcium (Ca) in the chondral and subchondral region was detected using high resolution synchrotron radiation induced micro X-ray fluorescence (SR mu-XRF) analysis. SR mu-XRF line scans in conventional and SR mu-XRF area scans in confocal geometry were correlated to backscattered electron (BE) images visualizing the mineralized tissue. RESULTS: In all samples, we found a highly specific accumulation of Pb in the tidemark, the transition zone between calcified and non-calcified articular cartilage. Pb fluorescence intensities in the tidemark, which is thought to be a metabolically active mineralization front, were 13-fold higher when compared to subchondral bone. Pb intensities in the subchondral region were strongly correlated with Zn, but were distinctly different from Ca and Sr. CONCLUSIONS: The finding of the highly specific accumulation of lead in the tidemark of human articular cartilage is novel. However at this point, the exact mechanisms of the local Pb accumulation as well as its clinical implications are unknown.     

The structure of the human subchondral plate

To study the anatomy of subarticular bone and cartilage, fresh specimens of cartilage on bone from the human shoulder, hip and knee were treated with bleach or papain, or were fixed and decalcified. All were compared using scanning electron microscopy. Papain digestion selectively removed cartilage to the tidemark. The tidemark contour was highly variable; irregularities were indirectly related to degenerative lesions and were most prominent in peripheral non-weight-bearing areas of joints with central fibrillation. Decalcification exposed the interface between the bone and calcified cartilage. Collagen fibrils in articular cartilage did not interdigitate with those of bone. The subchondral bone was appositional, avascular, smooth and very thin in most areas of human joints. Perforations through subchondral bone or calcified cartilage were rare. Bleach maceration destroyed important details.     

The effect of varus stress on the moving rabbit knee joint

Unicompartmental osteoarthritis was produced by applying varus stress to moving rabbit knee joints. Degenerative changes were confined to the medial tibial and the medial femoral articular surfaces. Within the range of varus stress used, duration appears to be more important than magnitude of varus stress in determining the severity of cartilage damage. The calcified zone remained histologically unchanged despite advanced changes in the noncalcified zone superficial to the tidemark. Intrachondral degenerative cysts were frequently found in the basilar layers of the noncalcified cartilage adjacent to the tidemark where shear stresses were likely to be highest and diffusible nutrients least available. Highly cellular cartilaginous tissue was noted in the subchondral marrow spaces in the specimens with advanced cartilage degeneration. These areas appeared to be continuous with the overlying degenerated cartilage through gaps in the calcified cartilage. Subchondral bone did not show remarkable trabecular thickening despite advanced degenerative changes in the articular cartilage.     

Variations in articular calcified cartilage by site and exercise in the 18-month-old equine distal metacarpal condyle

OBJECTIVES: To interrelate articular calcified cartilage thickness, mineralisation density, tidemark count and tidemark linear accretion rate by site in the equine third metacarpal distal condyle. To determine the effects of exercise during early life on articular calcified cartilage. METHOD: Six of 12 pasture-raised Thoroughbred horses were exercised from 10 days old. Calcein labels were given 19 and 8 days prior to euthanasia at 18 months old. Osteochondral specimens were cut from the distal third metacarpal condyle and imaged using confocal scanning light microscopy (CSLM) and quantitative backscattered electron scanning electron microscopy (qBSE). Articular calcified cartilage thickness and total thickness mineralisation density were measured on montaged qBSE image sets, and inter-label mineralisation density, tidemark count and linear accretion rate measured on registered CSLM-qBSE image pairs. RESULTS: Calcified cartilage thickness, mineralisation density, tidemark count and linear accretion rate varied significantly between sites. Regions with thinner calcified cartilage had greater linear accretion rates, hence rapid chondroclastic resorption. Mineralisation density was positively correlated with linear accretion rate. Fewer multiple tidemarks were counted in regions with greater linear accretion rates. Lag time between the tidemark and cement line was estimated (180 days; in the range of 0-648 days). Exercise had little effect on measured parameters. CONCLUSION: The major determinant of articular calcified cartilage thickness is the rate of chondroclastic resorption, not tidemark linear accretion rate. Our evidence supports coupled, mechanosensitive regulation of chondroclastic resorption and linear accretion rate in articular calcified cartilage. Exercising pasture-reared foals causes little additional adaptation in distal third metacarpal articular calcified cartilage.     

Interaction between zonal populations of articular chondrocytes suppresses chondrocyte mineralization and this process is mediated by PTHrP

OBJECTIVE: Articular cartilage is separated from subchondral bone by the tidemark and a calcified cartilage zone. Advancement of the calcified region and tidemark duplication are both hallmarks of osteoarthritis (OA). Currently the mechanisms controlling post-natal articular cartilage mineralization are poorly understood. The objective of this study is to test the hypothesis that cellular communication between different cartilage layers regulates articular chondrocyte mineralization. DESIGN: Co-culture models were established to evaluate the interaction of chondrocytes derived from the surface, middle and deep zones of articular cartilage. The cultures were stimulated with triiodothyronine (T3) to promote chondrocyte hypertrophy. The effects of zonal chondrocyte interactions on chondrocyte mineralization were examined over time. RESULTS: Co-culture of deep zone chondrocytes (DZCs) with surface zone chondrocytes (SZCs) suppressed the T3-induced increase in alkaline phosphatase (ALP) activity and related mineralization. Moreover, SZC-DZC co-culture was associated with a significantly higher parathyroid hormone-related peptide (PTHrP) expression when compared to controls. When PTHrP(1-40) was added to the DZC-only culture, it suppressed DZC ALP activity similar to the inhibition observed in co-culture with SZC. In addition, treatment with PTHrP reversed the effect of T3 stimulation on the expression of hypertrophic markers (Indian hedgehog, ALP, matrix metalloproteinases-13, Type X collagen) in the DZC cultures. Moreover, blocking the action of PTHrP significantly increased ALP activity in SZC+DZC co-culture. CONCLUSION: Our findings demonstrate the role of zonal chondrocyte interactions in regulating cell mineralization and provide a plausible mechanism for the post-natal regulation of articular cartilage matrix organization. These findings also have significant implications in understanding the pathology of articular cartilage as well as devising strategies for functional cartilage repair.     

Barrier to material transfer at the bone-cartilage interface: measurement with hydrogen gas in vivo

Hydrogen gas was used as a tracer to identify the barrier to material transfer at bone-cartilage interface in the rabbit knees in vivo. The transfer of hydrogen molecules from subchondral bone to articular cartilage was detected by means of platinum electrodes which were placed in varying depths in articular cartilage and subchondral bone. Hydrogen transfer was obstructed at the osteochondral junction in mature animals, while in immature animals there was no such barrier present in the bone-cartilage interface. The metabolism of articular cartilage in mature animals may be isolated from that of the underlying bone. All layers of the mature cartilage including those in the zone of calcified cartilage can receive nourishment and be maintained from the synovial fluid alone.     

Solute transport in the deep and calcified zones of articular cartilage

OBJECTIVES: (1) To establish whether the tidemark and calcified cartilage are permeable to low molecular weight solutes, thereby providing a potential pathway for nutrition of cells in the deep cartilage. (2) To investigate transport from the subchondral microcirculation into calcified cartilage in an intact perfused joint and the effects on transport of static loading. METHODS: The permeability of the tidemark and calcified cartilage was investigated in plugs of cartilage and subchondral bone which formed the membrane of a diffusion cell. Transport from the subchondral microcirculation and the effects of load were studied in an intact perfused joint. Both preparations used the metacarpophalangeal joints of mature horses and fluorescein and rhodamine (m.w. approximately 400 Da) were employed as tracers, assayed by quantitative fluorescence microscopy on histological sections. RESULTS: Calcified cartilage was permeable to both solutes, both from the superficial and the subchondral sides. The effective diffusivity of both solutes was of the order of 9 x 10(-9) cm(2) s(-1), fivefold less than in the uncalcified cartilage. The calcified zone was heterogeneous, with high uptake of both tracers in the vicinity of the tidemark. The distribution volume of rhodamine B was higher than for fluorescein, consistent with a significant anionic charge in the calcified matrix. Static loading of the intact joint did not affect the transport of rhodamine B but caused a significant decrease in concentration of fluorescein both in the surface and deep zones of the tissue. CONCLUSIONS: Calcified cartilage is permeable to small solutes and the subchondral circulation may make a significant contribution to the nutrition of deep cartilage in the mature horse. Static loading reduces the uptake of small anionic solutes in the intact joint.