Absolute concentrations of mRNA for type I and type VI collagen in the canine meniscus in normal and ACL-deficient knee joints obtained by RNase protection assay

Cellular and molecular meniscal changes in the degenerative knee: a review

Background

The important role of knee menisci to maintain adequate knee function is frequently impaired since early stages of knee joint degeneration. A better understanding of meniscal impairment may help the orthopaedic surgeon to orient the treatment of the degenerative knee. This review focuses on changes in meniscal cells and matrix when degeneration is in progress.

Main body

Differences in the meniscal structure and metabolism have been investigated in the degenerative knee, both in experimental animal models and in surgical specimens. Cell population reduction, extracellular matrix disorganization, disturbances in collagen and non-collagen protein synthesis and/or expression have been found in menisci along with knee degeneration. These changes are considered disease-specific, different from those due to aging.

Conclusion

Significant cellular and matrix differences are found in menisci during knee degeneration. These investigations may help to further progress in the understanding of knee degeneration and in the search of more biological treatments.

Transcriptome comparison of meniscus from patients with and without osteoarthritis

OBJECTIVE

To assess the impact of osteoarthritis (OA) on the meniscus by comparing transcripts and biological processes in the meniscus between patients with and without OA.

DESIGN

RNA microarrays were used to identify transcripts differentially expressed (DE) in meniscus obtained from 12 OA and 12 non-OA patients. The non-OA specimens were obtained at the time of arthroscopic partial meniscectomy. Real-time PCR was performed on selected transcripts. Biological processes and gene-networking was examined computationally. Transcriptome signatures were mapped with 37 OA-related transcripts to evaluate how meniscus gene expression relates to that of OA cartilage.

RESULTS

We identified 168 transcripts significantly DE between OA (75 elevated, 93 repressed) and non-OA samples (≥1.5-fold). Among these, CSN1S1, COL10A1, WIF1, and SPARCL1 were the most prominent transcripts elevated in OA meniscus, POSTN and VEGFA were most highly repressed in OA meniscus. Transcripts elevated in OA meniscus represented response to external stimuli, cell migration and cell localization while those repressed in OA meniscus represented histone deacetylase activity (related to epigenetics) and skeletal development. Numerous long non-coding RNAs (lncRNAs) were DE between the two groups. When segregated by OA-related transcripts, two distinct clustering patterns appeared: OA meniscus appeared to be more inflammatory while non-OA meniscus exhibited a "repair" phenotype.

CONCLUSIONS

Numerous transcripts with potential relevance to the pathogenesis of OA are DE in OA and non-OA meniscus. These data suggest an involvement of epigenetically regulated histone deacetylation in meniscus tears as well as expression of lncRNAs. Patient clustering based on transcripts related to OA in articular cartilage confirmed distinct phenotypes between injured (non-OA) and OA meniscus.

A Porcine Animal Model for Early Meniscal Degeneration - Analysis of Histology, Gene Expression and Magnetic Resonance Imaging Six Months after Resection of the Anterior Cruciate Ligament

BACKGROUND/OBJECTIVE

The menisci of the mammalian knee joint balance the incongruence between femoral condyle and tibial plateau and thus menisci absorb and distribute high loads. Degeneration processes of the menisci lead to pain syndromes in the knee joint. The origin of such degenerative processes on meniscal tissue is rarely understood and may be described best as an imbalance of anabolic and catabolic metabolism. A standardized animal model of meniscal degeneration is needed for further studies. The aim of the current study was to develop a porcine animal model with early meniscal degeneration.

MATERIAL AND METHODS

Resection of the anterior cruciate ligament (ACLR) was performed on the left knee joints of eight Göttingen minipigs. A sham operation was carried out on the right knee joint. The grade of degeneration was determined 26 weeks after the operation using histology and magnetic resonance imaging (MRI). Furthermore, the expression of 14 genes which code for extracellular matrix proteins, catabolic matrix metalloproteinases and inflammation mediators were analyzed.

RESULTS

Degenerative changes were detected by a histological analysis of the medial meniscus after ACLR. These changes were not detected by MRI. In terms of their gene expression profile, these degenerated medial menisci showed a significantly increased expression of COL1A1.

CONCLUSION

This paper describes a new animal model for early secondary meniscal degeneration in the Göttingen minipig. Histopathological evidence of the degenerative changes could be described. This early degenerative changes could not be seen by NMR imaging.

Genome-wide expression profiles of subchondral bone in osteoarthritis

Introduction

The aim of this study was to evaluate, for the first time, the differences in gene expression profiles of normal and osteoarthritic (OA) subchondral bone in human subjects.

Methods

Following histological assessment of the integrity of overlying cartilage and the severity of bone abnormality by micro-computed tomography, we isolated total RNA from regions of interest from human OA (n = 20) and non-OA (n = 5) knee lateral tibial (LT) and medial tibial (MT) plateaus. A whole-genome profiling study was performed on an Agilent microarray platform and analyzed using Agilent GeneSpring GX11.5. Confirmatory quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis was performed on samples from 9 OA individuals to confirm differential expression of 85 genes identified by microarray. Ingenuity Pathway Analysis (IPA) was used to investigate canonical pathways and immunohistochemical staining was performed to validate protein expression levels in samples.

Results

A total of 972 differentially expressed genes were identified (fold change ≥ ± 2, P ≤0.05) between LT (minimal degeneration) and MT (significant degeneration) regions from OA samples; these data implicated 279 canonical pathways in IPA. The qRT-PCR data strongly confirmed the accuracy of microarray results (R² = 0.58, P <0.0001). Novel pathways were identified in this study including Periostin (POSTN) and Leptin (LEP), which are implicated in bone remodeling by osteoblasts.

Conclusions

To the best of our knowledge, this study represents the most comprehensive direct assessment to date of gene expression profiling in OA subchondral bone. This study provides insights that could contribute to the development of new biomarkers and therapeutic strategies for OA.

Altered trabecular bone structure and delayed cartilage degeneration in the knees of collagen VI null mice

Mutation or loss of collagen VI has been linked to a variety of musculoskeletal abnormalities, particularly muscular dystrophies, tissue ossification and/or fibrosis, and hip osteoarthritis. However, the role of collagen VI in bone and cartilage structure and function in the knee is unknown. In this study, we examined the role of collagen VI in the morphology and physical properties of bone and cartilage in the knee joint of Col6a1(-/-) mice by micro-computed tomography (microCT), histology, atomic force microscopy (AFM), and scanning microphotolysis (SCAMP). Col6a1(-/-) mice showed significant differences in trabecular bone structure, with lower bone volume, connectivity density, trabecular number, and trabecular thickness but higher structure model index and trabecular separation compared to Col6a1(+/+) mice. Subchondral bone thickness and mineral content increased significantly with age in Col6a1(+/+) mice, but not in Col6a1(-/-) mice. Col6a1(-/-) mice had lower cartilage degradation scores, but developed early, severe osteophytes compared to Col6a1(+/+) mice. In both groups, cartilage roughness increased with age, but neither the frictional coefficient nor compressive modulus of the cartilage changed with age or genotype, as measured by AFM. Cartilage diffusivity, measured via SCAMP, varied minimally with age or genotype. The absence of type VI collagen has profound effects on knee joint structure and morphometry, yet minimal influences on the physical properties of the cartilage. Together with previous studies showing accelerated hip osteoarthritis in Col6a1(-/-) mice, these findings suggest different roles for collagen VI at different sites in the body, consistent with clinical data.

Zonal differences in meniscus matrix turnover and cytokine response

OBJECTIVE

To determine the mechanisms of meniscal degeneration and whether this varied zonally and from articular cartilage.

DESIGN

Normal ovine menisci were dissected into inner and outer zones and along with cartilage cultured ±IL-1α and TNFα. Glycosaminoglycan (GAG) and collagen release, and gene expression were quantified. Aggrecan proteolysis was analysed by Western blotting with neoepitope-specific antibodies. Matrix metalloproteinase (MMP)2, MMP9 and MMP13 activity was evaluated by gelatin zymography or fluorogenic assay.

RESULTS

Inner meniscus was more cartilaginous containing more GAG and expressing more ACAN and COL2A1 than outer zones. Higher expression of VCAN and ADAMTS4 in medial outer and both zones of the lateral meniscus reflected their embryologic origin from cells outside the cartilage anlagen. All meniscal regions released a greater % GAG in response to cytokines; only outer zones had cytokine-stimulated collagenolysis. Cytokine-induced aggrecanolysis was primarily due to increased ADAMTS cleavage in cartilage and inner menisci but MMPs in the outer menisci. Outer menisci always released more active MMP2 than other tissues and more active MMP13 in basal and TNF-stimulated cultures. Expression of ACAN, COL1A1 and COL2A1 was decreased by both cytokines in all tissues, while VCAN was increased by IL-1α in cartilage and inner menisci. Metalloproteinase expression was differentially regulated by IL-1α and TNFα: ADAMTS4, MMP1, MMP3 were upregulated more by IL-1α in inner zones whereas ADAMTS5, MMP13 and MMP9 were more upregulated by TNFα in outer zones.

CONCLUSIONS

Meniscal degeneration mechanisms are zonally-dependent, and may contribute to the enzymatic burden in the joint.

Changes of human menisci in osteoarthritic knee joints

OBJECTIVE

To investigate the changes of knee menisci in osteoarthritis (OA) in human.

METHODS

OA and control menisci were obtained from 42 end-stage OA knees with medial involvement and 28 non-arthritic knees of age-matched donors, respectively. The change of menisci in OA was evaluated by histology, and gene expression of major matrix components and anabolic factors was analyzed in the anterior horn segments by quantitative PCR (qPCR). In those regions of menisci, the rate of collagen neo-synthesis was evaluated by [(3)H]proline incorporation, and the change of matrix was investigated by ultrastructural observation and biomechanical measurement.

RESULTS

In OA menisci, the change in histology was rather moderate in the anterior horn segments. However, despite the modest change in histology, the expression of type I, II, III procollagens was dramatically increased in those regions. The expression of insulin-like growth factor 1 (IGF-1) was markedly enhanced in OA menisci, which was considered to be responsible, at least partly, for the increase in procollagen gene expression. Interestingly, in spite of marked increase in procollagen gene expression, incorporation of [(3)H]proline increased only modestly in OA menisci, and impaired collagen synthesis was suggested. This finding was consistent with the results of ultrastructural observation and biomechanical measurement, which indicated that the change of meniscal matrix was modest in the macroscopically preserved areas of OA menisci.

CONCLUSION

Although the expression of major matrix components was markedly enhanced, matrix synthesis was enhanced only modestly, and the changes of matrix in human OA menisci were rather modest in the non-degenerated areas.

Transfer of macroscale tissue strain to microscale cell regions in the deformed meniscus

Cells within fibrocartilaginous tissues, including chondrocytes and fibroblasts of the meniscus, ligament, and tendon, regulate cell biosynthesis in response to local mechanical stimuli. The processes by which an applied mechanical load is transferred through the extracellular matrix to the environment of a cell are not fully understood. To better understand the role of mechanics in controlling cell phenotype and biosynthetic activity, this study was conducted to measure strain at different length scales in tissue of the fibrocartilaginous meniscus of the knee joint, and to define a quantitative parameter that describes the strain transferred from the far-field tissue to a microenvironment surrounding a cell. Experiments were performed to apply a controlled uniaxial tensile deformation to explants of porcine meniscus containing live cells. Using texture correlation analyses of confocal microscopy images, two-dimensional Lagrangian and principal strains were measured at length scales representative of the tissue (macroscale) and microenvironment in the region of a cell (microscale) to yield a strain transfer ratio as a measure of median microscale to macroscale strain. The data demonstrate that principal strains at the microscale are coupled to and amplified from macroscale principal strains for a majority of cell microenvironments located across diverse microstructural regions, with average strain transfer ratios of 1.6 and 2.9 for the maximum and minimum principal strains, respectively. Lagrangian strain components calculated along the experimental axes of applied deformations exhibited considerable spatial heterogeneity and intersample variability, and suggest the existence of both strain amplification and attenuation. This feature is consistent with an in-plane rotation of the principal strain axes relative to the experimental axes at the microscale that may result from fiber sliding, fiber twisting, and fiber-matrix interactions that are believed to be important for regulating deformation in other fibrocartilaginous tissues. The findings for consistent amplification of macroscale to microscale principal strains suggest a coordinated pattern of strain transfer from applied deformation to the microscale environment of a cell that is largely independent of these microstructural features in the fibrocartilaginous meniscus.

Comparative spatial and temporal localisation of perlecan, aggrecan and type I, II and IV collagen in the ovine meniscus: an ageing study

This is the first study to immunolocalise perlecan in meniscal tissues and to demonstrate how its localisation varied with ageing relative to aggrecan and type I, II and IV collagen. Perlecan was present in the middle and inner meniscal zones where it was expressed by cells of an oval or rounded morphology. Unlike the other components visualised in this study, perlecan was strongly cell associated and its levels fell significantly with age onset and cell number decline. The peripheral outer meniscal zones displayed very little perlecan staining other than in small blood vessels. Picrosirius red staining viewed under polarised light strongly delineated complex arrangements of slender discrete randomly oriented collagen fibre bundles as well as transverse, thick, strongly oriented, collagen tie bundles in the middle and outer meniscal zones. The collagen fibres demarcated areas of the meniscus which were rich in anionic toluidine blue positive proteoglycans; immunolocalisations confirmed the presence of aggrecan and perlecan. When meniscal sections were examined macroscopically, type II collagen localisation in the inner meniscal zone was readily evident in the 2- to 7-day-old specimens; this became more disperse in the older meniscal specimens. Type I collagen had a widespread distribution in all meniscal zones at all time points. Type IV collagen was strongly associated with blood vessels in the 2- to 7-day-old meniscal specimens but was virtually undetectable at the later time points (>7 month).

Characterisation of human knee meniscus cell phenotype

OBJECTIVE

Studies on the biology of the human meniscus cell are scarce. The objective of our studies was to assess survival/proliferation of human meniscus cells in different culture conditions and to characterize the extracellular matrix (ECM) produced by these cells in these artificial environments. The composition of this ECM offers a variable to define the distinct meniscus cell phenotype.

MATERIALS AND METHODS

Human meniscus cells were isolated enzymatically from visually intact lateral and medial knee menisci. Cells were cultured in monolayer conditions or in alginate gel. The composition of the cell-associated matrix (CAM) accumulated by the isolated cells during culture was investigated and compared to the CAM of articular chondrocytes cultured in alginate using flow cytometry with fluorescein isothiocyanate-conjugated monoclonal antibodies against type I collagen, type II collagen and aggrecan. Additional cell membrane markers analysis was performed to further identify the different meniscus cell populations in the alginate culture conditions and meniscus tissue sections. Proliferation was analyzed using the Hoechst 33258 dye method. In some experiments, the effect of TGFbeta1 on some of these variables was investigated.

RESULTS

The CAM of monolayer cultured meniscus cells is composed of high amounts of type I and II collagen and low amounts of aggrecan. A major population of alginate cultured meniscus cells on the other hand synthesized a CAM containing high amounts of type I collagen, low amounts of type II collagen and high amounts of aggrecan. This population is CD44+CD105+CD34-CD31-. In contrast, a minor cell population in the alginate culture did not accumulate ECM and was mainly CD34+. The CAM of alginate cultured articular chondrocytes is composed of low amounts of type I collagen, high amounts of type II collagen and aggrecan. The expression of aggrecan and of type II collagen was increased by the addition of TGFbeta1 to the culture medium. The proliferation of meniscus cells is increased in the monolayer culture conditions. Cell numbers decrease slightly in the alginate culture, but can be increased after the addition of TGFbeta1.

CONCLUSION

These results demonstrate that the human meniscus is populated by different cell types which can be identified by a distinct CAM composition and membrane marker expression. Unlike the monolayer culture conditions, the alginate culture conditions appear to favor a more fibrochondrocyte-like cell accumulating a CAM resembling the native tissue composition. This CAM composition is distinctly different from the CAM composition of phenotypically stable articular cartilage chondrocytes cultured in the same alginate matrix.

Spatial organization of types I and II collagen in the canine meniscus

The meniscus of the knee joint is a fibrocartilage mainly composed of type I collagen and smaller amounts of type II collagen. The distribution of type II collagen in the canine meniscus and its spatial relationship to type I collagen was examined by immunohistochemistry and confocal microscopy. Dorsal and coronal slices of the mid-section of medial and lateral menisci from the knee joints of skeletally mature dogs were predigested with Streptomyces hyaluronate lyase and bacterial Protease enzyme XXIV. Monoclonal antibodies against type I collagen (CP17L) and type II collagen (II-II6B3) and an anti-type II collagen polyclonal antibody (AB759) were employed. The staining for type II collagen in the extracellular matrix of hyaline articular cartilage was diffuse without any identifiable spatial organization. In striking contrast, type II collagen in the fibrocartilage of the meniscus stained as an organized network. Type II collagen was distributed throughout the meniscus with the exception of the outer zone containing the blood vessels. Coronal and dorsal staining of the meniscus showed bundles of circumferential fibrils of type I that colocalized with type II collagen in specific sites. These bundles were enwrapped in a second organizational fibrillar system of types I and II collagen that also colocalized. Bundles of circumferential fibrils appeared in cross-section in coronal sections as dots within the interstitial spaces framed by the network of types I and II collagen of the second system. Confocal overlays showed that types I and II collagens were superimposed, suggesting a close spatial proximity between the two collagens. The cells were confined to the types I and II collagen fibrils that enwrapped the bundles. A striking feature of the radial tie fibers was patches of type II collagen without colocalized type I collagen. Our study reveals a unique network of type II collagen in fibrocartilage of the meniscus that serves as a morphological distinction between fibro- and hyaline cartilage.

The concentration, gene expression, and spatial distribution of aggrecan in canine articular cartilage, meniscus, and anterior and posterior cruciate ligaments: a new molecular distinction between hyaline cartilage and fibrocartilage in the knee joint

The concentration, spatial distribution, and gene expression of aggrecan in meniscus, articular cartilage, and the anterior and posterior cruciate ligaments (ACL and PCL) was determined in the knee joints of five mature dogs. An anti-serum against peptide sequences specific to the G1 domain of aggrecan was employed in competitive-inhibition ELISA of guanidine HCl extracts and immunofluorescence microscopy. Gene expression was determined by Taqman real-time PCR. The concentration of aggrecan in articular cartilage (240.1 +/- 32 nMol/g dry weight) was higher than that in meniscus (medial meniscus: 33.4 +/- 4.3 nMol/g) and ligaments (ACL: 6.8 +/- 0.9 nMol/g). Aggrecan was more concentrated in the inner than the outer zone of the meniscus. Aggrecan in meniscus showed an organized, spatial network, in contrast to its diffuse distribution in articular cartilage. Thus, differences in the concentration, gene expression, and spatial distribution of aggrecan constitute another molecular distinction between hyaline cartilage and fibrocartilage of the knee.

Comparison of the effects of caudal pole hemi-meniscectomy and complete medial meniscectomy in the canine stifle joint

OBJECTIVE

To compare the effects of caudal pole hemi-meniscectomy (CPHM) and complete medial meniscectomy (MM), specifically with respect to development of secondary osteoarthritis, in the stifle joints of clinically normal dogs.

ANIMALS

14 large-breed dogs.

PROCEDURE

Unilateral CPHM (7 dogs) or MM (7) was performed, and the left stifle joints served as untreated control joints. Gait was assessed in all dogs before surgery and at 4, 8, 12, and 16 weeks postoperatively. After euthanasia, joints were evaluated grossly; Mankin cartilage scores, subchondral bone density assessment, and articular cartilage proteoglycan extraction and western blot analyses of 3B3(-) and 7D4 epitopes were performed.

RESULTS

Weight distribution on control limbs exceeded that of treated limbs at 4 and 16 weeks after surgery in the CPHM group and at 4 and 8 weeks after surgery in the MM group; weight distribution was not significantly different between the 2 groups. After 16 weeks, incomplete meniscal regeneration and cartilage fibrillation on the medial aspect of the tibial plateau and medial femoral condyle were detected in treated joints in both groups. Mankin cartilage scores, subchondral bone density, and immunoexpression of 3B3(-) or 7D4 in articular cartilage in CPHM- or MM-treated joints were similar; 7D4 epitope concentration in synovial fluid was significantly greater in the MM-treated joints than in CPHM-treated joints.

CONCLUSIONS AND CLINICAL RELEVANCE

Overall severity of secondary osteoarthritis induced by CPHM and MM was similar. Investigation of 7D4 epitope concentration in synovial fluid suggested that CPHM was associated with less disruption of chondrocyte metabolism.

Congruency Effects on Load Bearing in Diarthrodial Joints

Modelling load bearing in diarthrodial joints is challenging, due to the complexity of the materials, the boundary and interface conditions and the geometry. The articulating surfaces are covered with cartilage layers that are filled with a fluid that plays a major role in load bearing [Mow, V.C., Holmes, M.H., Lai, W.M. (1984) "Survey article: fluid transport and mechanical properties of articular cartilage: a review", Journal of Biomechanics 17(5), 377-394]. Researchers have tended to approximate joint geometry using axisymmetry [Donzelli, P.S., Spilker, R.L., Ateshian, G.A., Mow, V.C. (1999) "Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure", Journal of Biomechanics 32, 1037-1047], often with a rounded upper articulating surface, creating a form of Hertz problem [Donzelli, P.S., Spilker, R.L., Ateshian, G.A., Mow, V.C. (1999) "Contact analysis of biphasic transversely isotropic cartilage layers and correlations with tissue failure", Journal of Biomechanics 32, 1037-1047]. However, diarthrodial joints (shoulder, hip and knee) are equipped with peripheral structures (glenoid labrum, acetabular labrum and meniscus, respectively) that tend to deepen the joint contact and thus cause initial contact to be established at the periphery of the joint rather than "centrally". The surface geometries are purposefully incongruent, and the incongruency has a significant effect on the stresses, pressures and pressure gradients inside the tissue. The models show the importance of the peripheral structures and the incongruency from a load-bearing perspective. Joint shapes must provide a compromise between demands for load-bearing, lubrication and the supply of nutrients to the chondrocytes of the cartilage and cells of the peripheral structures. Retention and repair of the functionality of these peripheral structures should be a prime consideration in any surgical treatment of an injured joint.

Analysis of cartilage biomarkers in the early phases of canine experimental osteoarthritis

OBJECTIVE

To study 3 body fluids for changes in the levels of 5 biomarkers of cartilage metabolism during the early phases of experimental osteoarthritis (OA).

METHODS

Twenty skeletally mature mixed-breed canines underwent unilateral surgical transection of the anterior cruciate ligament. Samples of joint fluid, serum, and urine were obtained preoperatively and just before necropsy (3 weeks or 12 weeks postoperatively). Biomarkers included 2 markers of cartilage matrix synthesis/turnover (aggrecan 846 epitope and C-propeptide of type II collagen) and 3 markers of cartilage degradation (keratan sulfate proteoglycan epitope, the collagenase-generated cleavage epitope of type II collagen [Col2-3/4C(long mono), or CIIC], and crosslinked peptides from the C-telopeptide domain of type II collagen [Col2CTx]). Significant changes in the levels of these biomarkers were determined by paired analyses.

RESULTS

Joint pathology was more severe in the 12-week group compared with the 3-week group. In joint fluid, due to limited volume, only Col2-3/4C(long mono) and Col2CTx were measured. Significant elevations in the levels of both of these markers were observed in experimental joints in both the 3-week group and the 12-week group. In serum, the level of aggrecan 846 epitope was elevated at both 3 weeks and 12 weeks, the level of Col2-3/4C(long mono) was elevated at 12 weeks, and the level of Col2CTx was elevated at both 3 weeks and 12 weeks. In urine, the level of Col2-3/4C(long mono) was elevated at 12 weeks after surgery.

CONCLUSION

Levels of biomarkers of intact aggrecan proteoglycan (aggrecan 846 epitope) and type II collagen degradation (Col2-3/4C(long mono) and Col2CTx) were elevated early after unilateral stifle joint injury, suggesting that these markers are sensitive and specific for early cartilage changes associated with isolated joint injury in this established model of experimental OA.

Differential effects of static and dynamic compression on meniscal cell gene expression

Cells of the meniscus are exposed to a wide range of time-varying mechanical stimuli that may regulate their metabolic activity in vivo. In this study, the biological response of the meniscus to compressive stimuli was evaluated in vitro, using a well-controlled explant culture system. Gene expression for relevant extracellular matrix proteins was quantified using real-time RT-PCR following a 24 h period of applied static (0.1 MPa compressive stress) or dynamic compression (0.08-0.16 MPa). Static and dynamic compression were found to differentially regulate mRNA levels for specific proteins of the extracellular matrix. Decreased mRNA levels were observed for decorin ( approximately 2.1 fold-difference) and type II collagen ( approximately 4.0 fold-difference) following 24 h of dynamic compression. Decorin mRNA levels also decreased following static compression ( approximately 4.5 fold-difference), as did mRNA levels for both types I ( approximately 3.3 fold-difference) and II collagen ( approximately 4.0 fold-difference). Following either static or dynamic compression, mRNA levels for aggrecan, biglycan and cytoskeletal proteins were unchanged. It is noteworthy that static compression was associated with a 2.6 fold-increase in mRNA levels for collagenase, or MMP-1, suggesting that the homeostatic balance between collagen biosynthesis and catabolism was altered by the mechanical stimuli. These findings demonstrate that the biosynthetic response of the meniscus to compression is regulated, in part, at the transcriptional level and that transcription of types I and II collagen as well as decorin may be regulated by common mechanical stimuli.

The effect of cranial cruciate ligament insufficiency on caudal cruciate ligament morphology: An experimental study in dogs

OBJECTIVES

To investigate the effect of cranial cruciate ligament (CrCL) insufficiency on morphology of the canine caudal cruciate ligament (CdCL).

STUDY DESIGN

In vivo experimental study.

ANIMALS

Five adult foxhounds.

METHODS

Two years after CrCL transection, the histologic appearance of CdCLs from CrCL-deficient and unoperated contralateral control (CrCL-intact) stifle joints were evaluated using light and transmission electron microscopy.

RESULTS

CdCLs from CrCL-deficient joints had extracellular matrix changes, characterized by chondroid metaplasia and disruption of cell architecture. Percent of small-diameter fibrils in CdCLs from CrCL-deficient joints was significantly greater (P <.05) than that in CdCLs from CrCL-intact joints. Collagen fibril density in CdCLs from CrCL-deficient joints (41.09 +/- 5.39%) tended to be less than that in CdCLs from CrCL-intact joints (52.96 +/- 6.92%); however, this difference was not significant (P =.056). Mean eccentricity (ratio of minor to major diameters) of collagen fibrils was significantly (P <.0001) lower for CdCLs from CrCL-deficient joints (0.85 +/- 0.016) when compared with that for CdCLs from CrCL-intact joints (0.87 +/- 0.015).

CONCLUSIONS

Significant alterations were found in the morphology of CdCLs from CrCL-deficient joints. These changes may be associated with repetitive microtrauma to the CdCL secondary to instability or enzymatic degradation in the hostile synovial environment of an unstable joint.

CLINICAL RELEVANCE

Regardless of the cause, the switch to a predominantly small-diameter collagen fibril profile may reflect compromised material properties of the CdCL. This should be taken into account when considering surgical techniques that rely on the CdCL to stabilize CrCL-deficient stifles.