ARTICULAR-CARTILAGE COLLAGEN BIREFRINGENCE IS ALTERED CONCURRENT WITHCHANGES IN PROTEOGLYCAN SYNTHESIS DURING DYNAMIC IN-VITRO LOADING

Introduction: The articular cartilage collagen network and proteoglyca ns are subject to changes in deteriorating joint diseases. In this stu dy, we exposed articular cartilage plugs to cyclic loading and investi gated the properties of collagen network, and proteoglycans in differe nt zones of the articular cartilage. Methods: Articular cartilage full -depth plugs were exposed in vitro to 4.1 MPa cyclic (0.5 Hz) loading for 1 to 20 hr and investigated using quantitative microscopic methods (i.e., polarized light microscopy, microspectrophotomery, and autorad iography). Results: The loading caused packing or condensation of the tissue. In histological sections, the height of uncalcified articular cartilage decreased by an average of 12.8% (range, 4 to 19.7%). Loadin g increased the birefringence of collagen in the superficial cartilage (P < 0.05), with thickening of the zone up to 41.4% at 20 hr. The thi ckness of the intermediate zone increased also (22% at 1 hr and 434% a t 20 hr). Concomitantly, the birefringence (P < 0.05) and the thicknes s of the deep zone decreased (18.5 to 27.8%). Loading for 4 hr increas ed the S-35-sulphate incorporation of the cartilage explants by an ave rage of 67% (P < 0.05). The increase was most significant in the deep cartilage. A simultaneous increase was observed in the proteoglycan co ncentration of the cartilage; the staining intensity with safranin-O i ncreased by 8.8% (P < 0.05). After 8 hr loading, this stimulation decr eased; at 20 hr, loading caused a clear inhibitory effect on proteogly can synthesis in the superficial zone. Discussion: According to these results, the chosen loading regimen increased the thickness and collag en orientation in the superficial zone. In contrast, the thickness and birefringence in the deep cartilage were reduced. The proteoglycan me tabolism of chondrocytes was first stimulated deep in the cartilage, b ut as the loading continued, the effect proved to be inhibitory (espec ially in the superficial part of uncalcified cartilage). (C) 1998 Wile y-Liss, Inc.