In vitro model of characterizing the effects of compressive loading on proteoglycans in anatomically intact articular cartilage.

An in vitro method has been developed of cultivating anatomically intact articular cartilage (humeral head of dog) while excluding both bone tissue and other connective tissues with a condom, which controls changes in hydration and minimizes loss of proteoglycans. Compressive loading experiments were carried out with the condom-covered humeral head, to which contact stresses of 2.1 MPa, 3.3 MPa and 6.4 MPa, respectively, were applied with a rubber disc of a simple loading apparatus. The model makes it possible, to compare experimentally loaded regions with experimentally unloaded regions in both the same joint area and the contralateral control joint. Intermittent pressure loading (4-s-on/16-s-off-cycle) during 2 hours of pulse-experiment and 18 hours of chase-experiment resulted in a 40% increase in proteoglycan synthesis rate at 2.1 MPa, an unaltered synthesis rate at 3.3 MPa, and a 45% decrease in proteoglycan synthesis rate at 6.4 MPa, as measured by 35S-sulfate incorporation. No significant increase in degradation rate of proteoglycans was noted during the various loading experiments.