Low‐intensity pulsed ultrasound (LIPUS) increases the articular cartilage type II collagen in a rat osteoarthritis model

In this study, the effect of low‐intensity pulsed ultrasound (LIPUS) on cartilage was evaluated in a rat osteoarthritis (OA) model using serum biomarkers such as CTX‐II (type II collagen degradation) and CPII (type II collagen synthesis) as well as histological criteria (Mankin score and immunohistochemical type II collagen staining). OA was surgically induced in the knee joint of rats by anterior cruciate/medial collateral ligament transection and medial meniscus resection (ACLT + MMx). Animals were divided into three groups: sham‐operated group (Sham), ACLT + MMx group without LIPUS (?LIPUS), and ACLT + MMx group with LIPUS (+LIPUS; 30 mW/cm², 20 min/day for 28 days). CTX‐II levels were elevated in both ?LIPUS and +LIPUS groups compared to that in the Sham group after the operation, but there was no significant difference between +LIPUS and ?LIPUS groups, suggesting that LIPUS does not affect the degradation of type II collagen in this model. In contrast, CPII was significantly increased in +LIPUS group compared to ?LIPUS and Sham. Moreover, histological damage on the cartilage (Mankin score) was ameliorated by LIPUS, and type II collagen was immunohistochemically increased by LIPUS in the cartilage of an OA model. Of interest, mRNA expression of type II collagen was enhanced by LIPUS in chondrocytes. Together these observations suggest that LIPUS is likely to increase the type II collagen synthesis in articular cartilage, possibly via the activation of chondrocytes and induction of type II collagen mRNA expression, thereby exhibiting chondroprotective action in a rat OA model. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:361–369, 2010     

Repair of full-thickness articular cartilage defects using injectable type II collagen gel embedded with cultured chondrocytes in a rabbit model

BACKGROUND: Recently, tissue-engineered chondrocyte transplantation has been tried to treat full-thickness cartilage defects. We developed an injectable type II collagen gel scaffold by chemically reacting type II collagen with polyethylene glycol crosslinker. This type II collagen was prepared from the nasal septa of cattle. In the present study, chondrocytes embedded in type II collagen gel were injected into rabbit full-thickness cartilage defects without a periosteal graft, and the feasibility for clinical application of the gel was evaluated. METHODS: Chondrocytes were isolated from 1-kg New Zealand white rabbits. A full-thickness articular cartilage defect (5 mm diameter, 4 mm depth) was created on the patellar groove of the femur of 16 male 3-kg New Zealand white rabbits. A type II collagen solution of mixed chondrocytes at a density of 1 x 10(7) cells/ml was injected and transplanted into the defect in the right knee. The controls were the defect only in the left knee. At 4, 8, 12, and 24 weeks after operation, four cases from each group were evaluated macroscopically and histologically. RESULTS: After injection into the cartilage defect, the gel bonded to the adjacent cartilage and bone within several minutes. Macroscopic examination revealed that the surface of the transplanted area was smooth and exhibited similar coloration and good integration with the surrounding cartilage at 12 and 24 weeks after transplantation. Histological examination at 8 weeks revealed favorable hyaline cartilage regeneration with good chondrocyte morphology. At 12 and 24 weeks, reparative cartilage remained rich in type II collagen. According to O'Driscoll histological scores, significant differences between the transplanted and control groups were apparent at 12 and 24 weeks. Immunohistochemical staining indicated sufficient type II collagen synthesis in regenerated cartilage 8 weeks after transplantation, and it was maintained until 24 weeks. CONCLUSIONS: These results indicate that type II collagen gel is suitable for injection into cartilage defects without any covering of a graft and offers a useful scaffold during chondrocyte transplantation.     

A type XI collagen mutation leads to increased degradation of type II collagen in articular cartilage

OBJECTIVE: To determine in articular cartilage whether degraded type II collagen is more abundant in Col11a1 mutant cho/+ than in age-matched +/+ mice and whether collagen degradation occurs in a generalized or localized fashion. DESIGN: Knee joints from cho/+ and +/+ mice at 6, 9, 12 and 15 months of age were dissected, fixed, cryosectioned, and stained with antibody COL2-3/4m against denatured type II collagen using a FITC-conjugated secondary antibody. Sections were viewed and photographed under a fluorescence microscope and areas of staining were quantified. RESULTS: Before 12 months of age, little degraded collagen staining was detectable in +/+ or cho/+ mice. By 15 months, however, cho/+ mice showed significantly more degraded type II collagen than age-matched controls. Degraded collagen staining was localized at the articular surface, not distributed generally throughout the articular cartilage. CONCLUSIONS: The results suggest a model in which cumulative biomechanical stresses trigger increased collagen synthesis and degradation in both +/+ and cho/+ mice at around 12 months of age. Cho/+ mice, however, are less able to synthesize and assemble normal replacement collagen fibrils because of the Col11a1 mutation. Degradation is further activated, resulting in the accumulation of degraded type II collagen in the articular cartilage extracellular matrix. Similar mutations that do not overtly affect skeletal development may likewise predispose humans to increased collagen degradation and resultant osteoarthritis.     

骨保护素对兔骨关节炎关节软骨的保护效应

目的 观察关节腔内注射骨保护素对兔骨关节炎关节软骨组织形态的保护作用.方法 将60只雄性新西兰大白兔随机分为三组,每组20只.骨保护素组行左侧膝关节前十字韧带离断术,术后4周于左膝关节腔内注射骨保护素溶液0.1 ml,每周注射5次,共注射8周;磷酸盐缓冲液组于前十字韧带离断术后4周注射等剂量磷酸盐缓冲液;假手术组显露前十字韧带后缝合切口.术后12周处死动物取左膝关节标本,行大体形态学Pelletier评分,切片番红染色后行Mankin软骨评分并测量软骨厚度.结果 大体观察骨保护素组股骨髁软骨评分(1.80±0.89)分,胫骨平台软骨评分(1.80±0.77)分,均低于磷酸盐缓冲液组[分别为(3.10±0.97)、(3.20±0.77)分],与假手术组比较差异无统计学意义.组织学观察骨保护素组的软骨结构(2.65±0.88)分、软骨细胞(1.35±0.71)分、番红染色(1.83±0.83)分、潮线完整性(0.30±0.47)分及Mankin软骨评分总分(6.13±1.97)分,均低于磷酸盐缓冲液组[分别为(4.52±1.09)、(1.85±0.63)、(2.80±0.75)、(0.65±0.49)、(9.83±1.98)分].骨保护素组Mankin评分总分高于假手术组,但四个分项评分与假手术组的差异无统计学意义.骨保护素组软骨厚度(371.84±38.94)μm,大于磷酸盐缓冲液组(255.09±74.82)μm,小于假手术组(404.68±15.97)μm,差异均有统计学意义.结论 骨保护素对关节软骨具有保护效应,可延缓骨关节炎进展.保护效应表现为减轻滑膜炎症反应、减少关节边缘骨赘形成及在一定程度上阻止软骨厚度丢失.     

Excessive degradation of type II collagen in articular cartilage in equine osteochondrosis.

Articular osteochondrosis (OCD) occurs in both man and animals. The etiology remains to be determined. Studies of OCD lesions in animals may provide clues as to its pathogenesis. The aim of our study was to determine whether there was evidence for increased degradation namely proteoglycan (PG) release and type II collagen cleavage in articular cartilage harvested from OCD lesions. We examined ex vivo explants at post-mortem from equine OCD lesions and macroscopically normal site and age matched cartilage. These were cultured over a 10 day period in serum-free medium. Type II collagen cleavage was measured in articular cartilage and media using an Elisa assay to detect the COL2-3/4C(short) epitope, which is generated on cleavage of the triple helix of type II collagen by collagenases. PG release was measured by a dye-binding assay. Cumulative release of PG and COL2-3/4C(short) and their contents in cartilage at the end of the culture period were determined. In OCD lesions there was a significant increase in type II collagen cleavage by collagenase but no evidence for increase of PG degradation. These findings point to a selective increase in type II collagen cleavage by collagenases, in OCD lesions of the kind observed in osteoarthritis. Further work is needed to determine whether changes represent primary or secondary events in the pathogenesis of OCD.     

Increase in degraded collagen type II in synovial fluid early in the rabbit meniscectomy model of osteoarthritis

OBJECTIVE: The objective of this study was to determine whether collagen type II breakdown products in synovial fluid (SF), detected by an enzyme-linked immunoassay, represent a useful marker for early events in osteoarthritis (OA) in the rabbit medial meniscectomy model. DESIGN: Complete medial meniscectomy was performed on the right knee joints of 32 rabbits. Balanced groups of rabbits were then sacrificed at 2, 4, 8, and 12 weeks post-surgery. An additional 8 unoperated and 11 sham-operated animals served as controls. SF lavages were performed on right and left knee joints of the same animals at sacrifice. The proteolytic epitope of type II collagen was monitored using an enzyme-linked immunoassay. RESULTS: Macroscopically visible surface fibrillation and focal erosions appeared as early as 2 weeks after meniscectomy in the femorotibial joint (P<0.01). OA developed gradually during the later observation period, and then predominantly on the medial tibial plateau and medial femur. Significant histological alterations in cartilage, including a loss of proteoglycans, surface irregularities, and clefts, were detected at 2 weeks after meniscectomy (P<0.01). Collagen type II epitope levels in SF lavage samples were elevated peaking at 2 weeks after meniscectomy (P<0.02). Levels decreased at later time points, but they were still raised at 12 weeks (P< or =0.05). Highly significant correlations were found between the SF collagen type II epitope levels and the macroscopic and microscopic scoring results (Spearman rho correlation coefficient, macroscopy-collagen type II epitope r=0.222, P=0.025; microscopy-collagen type II epitope r=0.436, P< or =0.01). CONCLUSION: In this rabbit model of medial meniscectomy, levels of type II collagen fragments in SF appear to provide a useful marker of the early degenerative changes.     

Matrilin-3 in human articular cartilage: increased expression in osteoarthritis

OBJECTIVE: Matrilin-3 is a member of the recently described matrilin family of extracellular matrix proteins containing von Willebrand factor A-like domains. The matrilin-3 subunit can form homo-tetramers as well as hetero-oligomers together with subunits of matrilin-1 (cartilage matrix protein). It has a restricted tissue distribution and is strongly expressed in growing skeletal tissues. Detailed information on expression and distribution of extracellular matrix proteins is important to understand cartilage function in health and in disease like osteoarthritis (OA). METHODS: Normal and osteoarthritic cartilage were systematically analysed for matrilin-3 expression, using immunohistochemistry, Western blot analysis, in situ hybridization, and quantitative PCR. RESULTS: Our results indicate that matrilin-3 is a mandatory component of mature articular cartilage with its expression being restricted to chondrocytes from the tangential zone and the upper middle cartilage zone. Osteoarthritic cartilage samples with only moderate morphological osteoarthritic degenerations have elevated levels of matrilin-3 mRNA. In parallel, we found an increased deposition of matrilin-3 protein in the cartilage matrix. Matrilin-3 staining was diffusely distributed in the cartilage matrix, with no cellular staining being detectable. In cartilage samples with minor osteoarthritic lesions, matrilin-3 deposition was restricted to the middle zone and to the upper deep zone. A strong correlation was found between enhanced matrilin-3 gene and protein expression and the extent of tissue damage. Sections with severe osteoarthritic degeneration showed the highest amount of matrilin-3 mRNA, strong signals in in situ hybridization, and prominent protein deposition in the middle and deep cartilage zone. CONCLUSION: We conclude that matrilin-3 is an integral component of human articular cartilage matrix and that the enhanced expression of matrilin-3 in OA may be a cellular response to the modified microenvironment in the disease.     

The organization of collagen in cryofractured rabbit articular cartilage: a scanning electron microscopic study

Adult rabbit articular cartilage was prepared for scanning electron microscopy using, in order, glutaraldehyde fixation, enzymatic removal of proteoglycan, dehydration in ethanol, cryofracture in liquid nitrogen, and critical-point drying. Enzymes were effective in fixed material. Fixation, cryofracture, alignment of fracture surfaces with "split lines," and retention of subchondral bone were found to be necessary steps for the preservation of collagen detail. The fibrous framework was found to be similar to that proposed by Benninghoff and favored by more recent phase-contrast microscopic studies. Vertical fibers extending from subchondral bone and a network of tangentially oriented superficial fibrils converge in the transitional zone. No random layer is seen. Pericellular capsules interdigitate with the vertical fibers. When cartilage is prepared in a manner that minimizes tissue damage, scanning electron microscopy provides useful, unique information.     

Type II collagen expression in the mandibular condyle during growth adaptation: An experimental study in the rabbit

Summary An experiment was designed to mimic orthopedic functional appliances in order to investigate the spatial and temporal characteristics of type II collagen secretion as a marker of cartilage maturation in the mandibular condyle of young rabbits. The position of the glenoid fossa in relation to the condyle was altered so that articulation now took place more posteriorly. Histological sections of the condyles of 15-, 20- and 30-day-old experimental and control animals were stained with toluidine blue and with an anti-type II collagen antibody. A widened progenitor cell layer was found posteriorly in the experimental condyles and a narrow layer was found anteriorly to the articulating region. The chondroblast layer was also widened posteriorly, whereas the hypertrophic cell zone was narrower; the opposite was seen anteriorly. The effect was marked in 15- and 20-day-old animals and weak in 30-day-old animals. Type II collagen stain and strong toluidine blue metachromasia were not observed in the progenitor cell zone until the chondroblasts had acquired a flattened, slightly hypertrophic morphology, which was found deeper in the experimental condyles than in the controls. This is interpreted as a slowing down of the differentiation of chondroblasts as a result of the force applied. The effect of masticatory function may also be explained in terms of delayed differentiation of chondroblasts and increased growth.     

The influence of vitamin D metabolites on the calcification of cartilage matrix and the C-propeptide of type II collagen (chondrocalcin)

The influence of vitamin D metabolites (at 1 X 10(-10) M) on the calcification of cartilage matrix (measured by 45Ca2+ uptake) and the C-propeptide of type II collagen (measured by radioimmunoassay) has been studied using organ cultures and chondrocytes isolated from growth plates of vitamin D-deficient and -sufficient 11-day-old rats. Vitamin D-deficient rats had reduced amounts of C-propeptide in their serum and freshly isolated growth plate chondrocytes. In all chondrocytes cultured from vitamin D-deficient animals, the C-propeptide content was maximal at 24 hr whereas calcification continued to increase for up to 72 hr. In organ and chondrocyte cultures of tissue from vitamin D-sufficient rats, both 1,25-dihydroxycholecalciferol (1,25(OH)2D3) and 24,25-dihydroxycholecalciferol (24,25(OH)2D3) were required for maximal stimulation of calcification and maximal increases in C-propeptide content. In these D-replete tissues, 24,25-(OH)2D3 had a less stimulatory effect on both calcification (organ and cell cultures) and C-propeptide (organ cultures only), while 1,25(OH)2D3 alone had no effect in cell cultures but an inhibitory effect in organ cultures. Studies of cells or tissue from growth plates of vitamin D-deficient rats demonstrated that 24,25(OH)2D3 alone produced maximal calcification and maximal increases in the C-propeptide content. 1,25(OH)2D3 generally had an inhibitory effect on both calcification and C-propeptide when used alone. In the presence of 1,25(OH)2D3, the stimulatory effect of 24,25(OH)2D3 was partly abrogated. Maximal stimulation of calcification and increases in C-propeptide by 24,25(OH)2D3 were observed at 1 X 10(-9) M and 1 X 10(-10) M. In none of these studies was there any effect on proteoglycan content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Type II collagen degradation in articular cartilage fibrillation after anterior cruciate ligament transection in rats

OBJECTIVE: To investigate the kinetics of early cartilage changes in mechanically induced osteoarthritis (OA) and the association of these changes with damage to the type II collagen network. METHODS: Experimental OA was induced by anterior cruciate ligament transsection in the rat knee joint (ACLT-OA). Animals were sacrificed after 2, 7, 14, 28 and 70 days. Knee joints were evaluated using routine histology and immunohistochemistry for denatured (unwound) type II collagen to detect collagen damage. An antibody recognizing the collagenase cleavage site in type II collagen was used to study the role of collagenase in this process. RESULTS: The first changes of the articular cartilage after anterior cruciate ligament transection occurred in the superficial zone. These changes included loss of superficial chondrocytes, swelling of the remaining chondrocytes and superficial fibrillation. The swelling of the chondrocytes did not result from a change towards the hypertrophic phenotype, since these cells did not stain for type X collagen. A marked increase in denatured type II collagen staining was present in the fibrillated areas. Staining of the collagenase cleavage site showed the same distribution as denatured collagen but was clearly less intense. Collagen damage could never be detected before fibrillation occurred and was not present in non-fibrillated areas. CONCLUSIONS: These results indicate that in this model cartilage degeneration starts at the articular surface and that this degeneration is associated with a localized expression of type II collagen degradation products.     

Developmental distribution of collagen type XII in cartilage: association with articular cartilage and the growth plate.

Collagen type XII is a member of the fibril-associated collagens and is characterized by a short triple-helical domain with three extended noncollagenous NC3 domains. Previous studies suggested that collagen XII is a component of cartilage but little is known about its spatial-temporal distribution. This study uses a polyclonal antibody to the purified NC3 domain to investigate its developmental distribution in rat forelimb. Collagen XII was present at the joint interzone on embryonic day 16 (E16d) and restricted to the presumptive articular cartilage by E18d. Labeling of the articular surface intensified as development progressed postnatally (day 1 [1d] to 28d) and extended approximately six cell diameters deep. In juvenile rats, collagen XII antibodies also labeled the longitudinal and transverse septa of stacked chondrocytes in the growth plate. However, collagen XII was not associated at any developmental stage with the cartilaginous secondary ossification center and was only weakly expressed in epiphyseal cartilage. Ultrastructural localization of the NC3 domain epitope showed labeling of the surface of collagen II fibrils both in tissue and in isolated fibrils. The results presented provide further evidence that articular cartilage differs substantially from the underlying epiphyseal cartilage and that different chondrocytic developmental fates are reflected in the composition of their extracellular matrix starting early in development. In addition, collagen XII was distributed in areas of cartilage with more organized fibril orientation and may have a role in promoting alignment or stabilizing such an organization, thereby creating a matrix capable of withstanding load-bearing forces.     

兔骨关节炎软骨缺损动物模型的建立

目的探讨建立一种便捷实用的兔骨关节炎软骨缺损动物模型的方法，以适应软骨组织工程技术修复骨关节炎软骨缺损研究的要求。方法5-7月龄新西兰大白兔22只，雌雄不限，体重2．5～3．0kg。根据侧别，分为改良侧（左侧膝）及对照侧（右侧膝）。改良侧分别切除兔内侧半月板、前十字韧带并在股骨髌沟部制造一直径4mm，深3mm的软骨缺损，对照侧仅切除内侧半月板和前十字韧带。分别在术后第3周和第6周在双侧股骨髁部和髌沟部取材，比较两种骨关节炎动物模型的大体形态及病理变化，进行Mankin评分及统计学分析。结果术后6周，改良侧股骨髌沟软骨缺损仍明显存在，但缺损面直径减小，股骨髌沟墨汁染色均达Ⅳ级，光学显微镜下示股骨髌沟软骨缺损达钙化层以下；而对照侧股骨髌沟墨汁染色均未达Ⅳ级。术后3周，改良侧股骨髌沟部Mankin法OA评分（11．82±1．07）分，对照侧（2．37±0．62）分；术后6周，改良侧股骨髌沟部Mankin法OA评分（13．29±1．15）分，对照侧（5．65±1．03）分；改良侧与对照侧股骨髌沟部Mankin评分比较差异有统计学意义（P〈0．01），但股骨髁部Mankin评分两组比较，差异无统计学意义（P〉0．05）。改良侧关节软骨退变进行性加重。结论改良侧和对照侧均能获得满意的骨关节炎动物模型。改良侧在股骨髌沟处形成一个明显的陈旧性软骨缺损，为应用软骨组织工程技术研究骨关节炎软骨缺损修复提供了一种便捷实用的动物模型。     

Ex vivo characterization of articular cartilage and bone lesions in a rabbit ACL transection model of osteoarthritis using MRI and micro-CT

OBJECTIVE: To characterize the rabbit anterior cruciate ligament transection (ACLT) model of osteoarthritis (OA) at various stages of disease using high-resolution 3-D medical imaging systems, which, in turn, will facilitate future longitudinal studies evaluating disease progression and response to therapy in live animals. METHODS: Degenerative changes in femorotibial cartilage, volumetric bone mineral density (vBMD), bone volume fraction (BV/TV), and osteophyte volume were characterized ex vivo using 4-T magnetic resonance imaging (MRI) and micro-computed tomography (micro-CT) at 4, 8, and 12 weeks post-ACLT. These changes were subsequently correlated to macroscopic joint evaluation. RESULTS: Macroscopic assessment demonstrated progressive cartilage degeneration post-surgery, which was significantly correlated to MRI evaluation (r=0.82, P<0.0001). Linear regression analysis indicated that vBMD and BV/TV are linearly related such that as vBMD increases, BV/TV increases (P<0.0001). Micro-CT revealed bone loss at 4 and 8 weeks post-ACLT, but recovery to control values at 12 weeks post-ACLT. Volumetric BMD was not strongly correlated with macroscopic assessment of articular cartilage degeneration (r=-0.35, P<0.0001). Quantitative measurement of osteophyte volume demonstrated a statistically significant difference (with respect to control groups) at both 8 and 12 weeks post-ACLT, but not at 4 weeks post-ACLT. CONCLUSIONS: The rabbit ACLT model of OA demonstrates progressive cartilage degeneration and intermediate bone changes at 4, 8, and 12 weeks post-surgery. Cartilage and bone lesions were characterized ex vivo using 4-T MRI and micro-CT, and MRI assessment of cartilage degeneration was correlated to macroscopic grading.     

Biomechanical, histologic and macroscopic assessment of articular cartilage in a sheep model of osteoarthritis

OBJECTIVES: Our primary objective was to explore the full potential of the ovine medial meniscectomy (MMx) model of early osteoarthritis (OA) for studies to validate non-destructive articular cartilage (AC) assessments and therapeutic interventions. Our secondary objective was to re-evaluate the relationships between the different types of AC assessment after MMx in sheep. METHODS: Macroscopic assessments, dynamic shear modulus (G*), phase lag and AC thickness measurements were performed at a total of 5437 reference points on all six articular surfaces in four normal joints and 16 MMx ovine stifle (knee) joints. Comparisons with histologic assessments of gross structural damage, collagen organisation (birefringence) and proteoglycan content were possible at 702 of these points. RESULTS: Histologic gross structural damage and proteoglycan loss were seen throughout the joint with greatest severity (fibrillation) in closest proximity to the MMx site. Increases in AC (30-50%) thickness, reductions in G* (30-40%) and collagen birefringence intensity (15-30%) occurred more evenly throughout the joint. Macroscopic softening was evident only when G* declined by 80%. G* correlated with AC thickness (rho=-0.47), collagen organisation rho=0.44), gross structural damage (rho=-0.44) and proteoglycan content (rho=0.42). Multivariate analysis showed that collagen organisation contributed twice as much to dynamic shear modulus (t=6.66 as proteoglycan content (t=3.21). Collagen organisation (rho=0.11) and proteoglycan content (rho=0.09) correlated only weakly to phase lag. CONCLUSIONS: Macroscopic assessments were insensitive to AC softening suggesting that arthroscopic assessments of AC status might also perform poorly. Collagen integrity was more important for the maintenance of AC stiffness (G*) than proteoglycan content. The development of major AC softening and thickening throughout the joint following MMx suggested involvement of non-mechanical (e.g., protein and biochemical) chemical and cytokine mediated processes in addition to the disturbance in biomechanical loading. The ovine MMx model provides a setting in which the spectrum of AC changes associated with the initiation and progression of OA may be evaluated.     

Comparison of collagenase-cleaved articular cartilage collagen in mice in the naturally occurring STR/ort model of osteoarthritis and in collagen-induced arthritis

OBJECTIVE: The STR/ort mouse develops a naturally occurring osteoarthritis of the femorotibial joint that provides a model with which to establish the time course of biochemical changes taking place in articular cartilage in the disease. Our objective was to define the onset, location and progression of type II collagen cleavage by collagenase in the tibial cartilage of the STR/ort mouse. For comparison, cartilage collagen cleavage was also studied in collagen-induced arthritis in DBA mice. DESIGN: STR and control CBA mice aged 6-45 weeks were examined. DBA/1 mice were studied 2 and 3 weeks after initiating collagen-induced arthritis. Collagen cleavage was detected by immunolocalization using the antibody COL2-3/4Cshort which recognizes a carboxy terminal neoepitope created by collagenase cleavage of type I and II collagens. RESULTS: No COL 2-3/4Cshort immunostaining was observed in the intact cartilage of healthy young or old mice. The earliest detectable collagen degradation occurred at the cartilage surface coincident with the appearance of surface roughening. As fibrillations developed, further collagen degradation was evident around the edge of the lesion and in adjacent extracellular matrix. In contrast, staining was observed throughout the cartilage matrix in type II collagen-induced arthritis prior to the development of histopathological lesions. CONCLUSION: No evidence was found for collagen cleavage in intact/pre-lesional cartilage from STR/ort mice. Local collagen cleavage was, however, clearly associated with very early histopathological lesions and immunostaining with COL 2-3/4Cshort increased with progression of the latter. In contrast, type II collagen cleavage occurs throughout the articular cartilage at an early stage in collagen-induced arthritis.     

Prediction of collagen orientation in articular cartilage by a collagen remodeling algorithm

OBJECTIVE: Tissue engineering is a promising method to treat damaged cartilage. So far it has not been possible to create tissue-engineered cartilage with an appropriate structural organization. It is envisaged that cartilage tissue engineering will significantly benefit from knowledge of how the collagen fiber orientation is directed by mechanical conditions. The goal of the present study is to evaluate whether a collagen remodeling algorithm based on mechanical loading can be corroborated by the collagen orientation in healthy cartilage. METHODS: According to the remodeling algorithm, collagen fibrils align with a preferred fibril direction, situated between the positive principal strain directions. The remodeling algorithm was implemented in an axisymmetric finite element model of the knee joint. Loading as a result of typical daily activities was represented in three different phases: rest, standing and gait. RESULTS: In the center of the tibial plateau the collagen fibrils run perpendicular to the subchondral bone. Just below the articular surface they bend over to merge with the articular surface. Halfway between the center and the periphery, the collagen fibrils bend over earlier, resulting in a thicker superficial and transitional zones. Near the periphery fibrils in the deep zone run perpendicular to the articular surface and slowly bend over to angles of -45 degrees and +45 degrees with the articular surface. CONCLUSION: The collagen structure as predicted with the collagen remodeling algorithm corresponds very well with the collagen structure in healthy knee joints. This remodeling algorithm is therefore considered to be a valuable tool for developing loading protocols for tissue engineering of articular cartilage.