Hyaline articular cartilage dissected by papain: light and scanning electron microscopy and micromechanical studies

The effect of normal saline irrigation at different temperatures on the surface of articular cartilage: an experimental study in the rat

PURPOSE

To determine, with an electron microscope, the effects of irrigation fluid at different temperatures on the surface of articular cartilage. TYPE OD STUDY: Experimental in vivo study.

METHODS

With a scanning electron microscope, we investigated the effect of 2 hours of irrigation with normal saline at 3 different temperatures (4 degrees C, 25 degrees C, and 37 degrees C) on articular hyaline cartilage in an in vivo rat knee model study. The contralateral knees were used as controls. We then compared the results.

RESULTS

Specimens irrigated with cold (4 degrees C) fluid seemed to show the most uneven surface and apparent fibril exposure. Those irrigated with fluid close to body temperature (37 degrees C) showed the most even surface without fibril exposure.

CONCLUSIONS

Although further work is needed to evaluate the long-term effects, using warm irrigation fluid to maintain the intra-articular environment at a more physiologically normal temperature may help reduce damage to cartilage during irrigation.

In vivo qualitative assessments of articular cartilage in the rabbit knee with high-resolution MRI at 3 T

Proteoglycan (PG) loss and disruption of the collagen framework in cartilage are early events associated with osteoarthritis (OA). The feasibility of in vivo high-resolution MRI assessments probing both macromolecules was explored in articular cartilage of the rabbit knee. One-millimeter thick coronal images were obtained at 3 T with a 97 x 97 microm(2) pixel size. A 22% decrease in the magnetization transfer (MT) exchange rate along with an approximately 2-fold greater Gd(DTPA)(2-)-induced decrease in T(1) relaxation time were measured in response to papain injection 1 day prior to the MRI session, indicative of an alteration of collagen integrity and PG depletion, respectively. A two-point method was tested as an alternative to the more time-consuming multipoint method typically used to measure T(1) changes. Kinetics of Gd(DTPA)(2-) uptake were observed with a 10-min time resolution. The diffusive transport of Gd(DTPA)(2-) was characterized by a T(1) decrease approximately 2-fold faster in papain-treated knees. These data suggest that kinetics of tracer diffusion may be used as an informative marker of PG loss, in addition to the amplitude of T(1) variations. When applied to a relevant OA model, the combination of MT and Gd(DTPA)(2-)-MRI may help in identifying new active compounds during efficacy studies on cartilage protection.

Histochemical studies of the extracellular matrix of human articular cartilage--a review

OBJECTIVE

This paper reviews the histochemistry of the extracellular matrix of human articular cartilage. No systematic review of histochemical knowledge and techniques in the study of articular cartilage has been published previously.

METHODS AND RESULTS

Literature was searched in the Winspirs Medline database from 1960 to 2000. Only techniques applicable for bright field or polarization microscopy were considered. Unless otherwise noted, all applies to hyaline cartilage. The most widely used fixatives are adequate for routine staining of proteins, but proteoglycan fixation is problematic, and no one fixative can be recommended. Proteoglycan can be stained reliably but it is problematic that, at low substrate concentrations, these methods are not stoichiometric. Collagen can be stained efficiently, although attempts to differentiate collagen types have not been successful.

CONCLUSIONS

Detailed studies of fixation and staining procedures should be carried out and standards for cartilage sampling, handling and evaluation agreed upon if results from different laboratories are to be compared.

Scanning electron microscopy of "fibrillated" and "malacic" human articular cartilage: technical considerations

Specimens of articular cartilage from human knees with gross evidence of malacia (dull appearance and/or softness) or fibrillation (exposed fibrous strands and/or staining with India ink) were prepared for scanning electron microscopy (SEM) and compared to cartilage from apparently intact regions. Vertical cryofractures were made through the center of each specimen, so the matrix collagen structure and its relationship to surface features could be examined. Soft, dull, malacic cartilage was characterized by the presence of numerous clefts among the collagen fibers within the most superficial region of the cartilage. In one form of this condition, these clefts did not extend through the articular surface. In a second form, usually observed where the tangential zone was normally thin or absent, the free ends of radial collagen fibers were exposed, but the deeper layers were intact. Two forms of fibrillation were also identified. The first is created by separation of the superficial lamellae which curl up from the tangential layer and form frondlike projections above the normal plane of the joint surface. In the second, deep radial fibers are exposed by vertical fissures. This second form is associated with advanced damage to the joint. The early stages of cartilage failure are characterized by debonding among the major collagen fiber tracts. This process may initiate in the deep tangential zone where the radial fibers cross into the surface. The patterns of the degenerative changes are dictated by the original architecture of the collagen matrix. The microscopic findings do not correlate adequately with conventional gross grading. SEM provides useful information about injured articular cartilage.

Ultrastructure of adult human articular cartilage matrix after cryotechnical processing

The ultrastructure of adult human articular cartilage matrix is reexamined in tissue processed according to recently improved cryotechniques [Studer et al. (1995) J. Microsc., 179:321-332]. In truely vitrified tissue, a network of fine cross-banded filaments (10-15 nm in diameter) with a periodicity characteristic of collagen fibrils is seen throughout the extracellular substance, even within the pericellular compartment, which has hitherto been deemed free of such components. Proteoglycans fill the interstices between these entities as a homogeneously distributed granular mass; they do not manifest a morphologically identifiable reticular structure. Longitudinally sectioned collagen fibrils exhibit variations in thickness and kinking; they tend to align with their periodic banding in register and are frequently seen to split or fuse along their longitudinal course. The tendency of fibrils to form bundles is greater in deeper zones than in more superficial ones. A duality in the orientation of fibrils and fibril bundles is observed within the interterritorial matrix compartment: superimposed upon the well-characterized arcade-like structure formed by one subpopulation is another, more randomly arranged one. The classical concepts of matrix organization thus need to be modified and refined to encompass these findings.

Problems and paradigms in joint pathology

This short review outlines aspects of joints relevant to current problems in articular, connective tissue disease and describes the pathology of rheumatoid arthritis and osteoarthrosis. The synovial joints display greatly varying degrees of anatomical specialisation. There is also heterogeneity of microscopic structure, to illustrate which the synovial components of the sacroiliac joints are considered. The chondron is regarded as a functional unit of hyaline articular cartilage but the responses of this tissue in disease are strongly influenced by its avascularity and by the need for chondrocytes to communicate with each other and with their local and systemic environments. Hyaline cartilage is capable of molecular replacement or substitution but not of repair by regeneration; it can, however, be replaced by fibrocartilage. The bearing surfaces of hyaline articular cartilage are never planar or smooth. Rheumatoid arthritis is a paradigm of connective tissue disease. It is not only a systemic disorder which may abbreviate life but, characteristically, is an aseptic form of symmetric polyarthritis. The inheritance of HLA-DR beta 1 and of female sex predispose to rheumatoid arthritis but the cause is unknown; it may be viral. Central to the disease is destruction of articular cartilage by sustained inflammation in which activated macrophages and TH cells, possibly of restricted clonality, combine to release cytokines, proteinases and the mediators of inflammation. Osteoarthrosis is a synovial joint syndrome, not a single disease. It is characterised by a loss of and change in the composition of cartilage proteoglycans leading to failure of normal responses to stress. The results include cartilage fibrillation and loss, bone exposure and a clinical syndrome of pain and disability. Rare forms of heritable chondrodysplasia lead to premature osteoarthrosis but, in most instances, the cause of osteoarthrosis appears to be either excess, inappropriate or insufficient mechanical demand, or traumatic, infective, inflammatory, endocrine or metabolic disease. There remain idiopathic ('primary') cases in which no cause is demonstrable.

Magnetic resonance imaging reflects cartilage proteoglycan degradation in the rabbit knee

Cartilage degeneration in osteoarthritis is initiated by a loss of proteoglycan. Intra-articular injection of papain causes a reversible loss of proteoglycan in rabbit knees. Rabbits were scanned with magnetic resonance imaging (MRI), using a 1.5T Signa superconducting magnet with 3 inch surface coil. Spin echo sequences were performed in the coronal and sagittal planes at 0, 24, 48, and 72 h after intra-articular injection of papain to obtain T1, proton density, and T2-weighted images. Cartilage proteoglycan content was measured biochemically and histochemically. Reduced articular cartilage thickness in the MR images of papain-treated knees corresponded to changes in cartilage proteoglycan content.

Synovial membrane and cartilage changes in experimental osteoarthrosis

The Hulth instability model was performed on 25 rabbit knee joints. Electron-microscopic, light-microscopic, and histomorphometric data demonstrated consistent chondrocyte alterations and cartilage destruction. The comparison between operated, sham, and control knees shows that surgical intervention without surgically induced instability is followed by changes in the synovial membrane and cartilage. The cartilage destruction is preceded by a synovial reaction, suggesting that the inflammatory response has an important role in the onset of cartilage damage in this model. The damage was more severe in the experimental knees, suggesting that mechanical instability is also a factor in cartilage destruction.