The incidence of enlarged chondrons in normal and osteoarthritic human cartilage and their relative matrix density

Objective: To quantitate changes in the pericellular matrix in osteoarthrit ic (OA) articular cartilage. Design Chondrons were enzymatically isolated from normal and OA human carti lage;The cross-sectional area of the chondrons were measured. After immunol abeling for keratan sulfate, type VI collagen and type II collagen, the rel ative matrix density was determined for different size classes of chondrons with quantitative fluorescence microscopy. Results: For individual chondrons, the average cross-sectional area (344+/- 28 mu m(2), mean+/-SE) for the normal specimens was significantly smaller t han the average area (439+/-30 mu m(2)) far the OA specimens. Using 496 mu m(2) (mean+2 SD of the normal area) as the cut-off for enlarged chondrons, 33% of individual OA chondrons were enlarged-compared to 16% for the normal . Chondrons under 300 mu m(2) had a significantly higher density of keratan sulfate and type VI collagen than larger chondrons, while chondrons over 4 00 mu m(2) had similar matrix densities. Conclusions: There is a higher incidence of enlarged chondrons in OA cartil age than in normal cartilage. The enlargement may initially be due to hydro dynamic swelling but further increases in size are due to increased matrix deposition. (C) 2000 OsteoArthritis Research Society International.