Abstract
Introduction: The surface of articular cartilage is adapted to low-friction movement. It is important for lubrication, resists shear and compression, and allows transfer of fluid, nutrients and metabolites between synovial fluid, matrix and cells. Surface damage is common following trauma and in early osteoarthritis. The use of intra-articular hyaluronan (visco-supplementation), or oral glucosamine and chondroitin, is claimed to enhance surface protection and/or repair. To validate such treatment biologically, a better understanding of normal structure and function of the cartilage surface is required.
Methods: The surface of femoral condylar cartilage of sheep was examined using transmission electron microscopy (TEM), scanning electron microscopy and polarising microscopy. Fresh specimens were obtained before and after wiping the surface with lens tissue.
Results: TEM of un-wiped normal cartilage showed a thin surface coating of amorphous electron-dense material containing occasional microvesicles and bundles of detaching collagen fibrils. In wiped cartilage this coating was absent, suggesting the superficial layer described in previous studies (lamina splendens of MacConaill), is an adherent coating, probably aggregated proteoglycan, hyaluronate and matrix degradation products. The definitive cartilage surface was a smooth network of fine collagen fibres supported by a mesh of collagen containing microvesicles and particles. More deeply a denser layer of collagen ran parallel to the joint surface. The most superficial zone would allow rapid surface exchange of fluid and particles while the deeper collagen would protect the underlying cells and limit fluid moving deeper during joint loading.
Conclusions: The findings have implications for therapy aimed at cartilage surface protection and/or repair.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
