EFFECTS OF CONTINUOUS DISTRACTION ON CARTILAGE IN A MOVING JOINT - ANINVESTIGATION ON ADULT-RABBITS

An animal model, using distraction force on adult rabbits, was develop ed to study the effects of nonweight-bearing on articular cartilage in a moving joint. Histologic evaluation was used to compare the morphol ogy of chondrocytes, safranin O intensity, cartilage thickness, and st ructural changes between the test and contralateral joints. At 3 and 6 weeks, the chondrocytes in superficial and intermediate zones were ro und, with an increase in cellular volume density and mean cell volume and with less metachromasia; the safranin O intensity and cartilage th ickness were the same as in the controls,ln cartilage of the 9-week gr oup, mean cell volume decreased with cell cloning in the superficial z one, while numerical density increased and mean matrix volume per cell decreased in the superficial and intermediate zones. The cartilage, w ith a 34% reduction in thickness and a 53-72% decrease in safranin O i ntensity from the superficial to the deep zone, had superficial fibrot ic proliferation, surface erosion or depression, and tidemark irregula rity, Continuous distraction in a moving joint caused morphological ch anges in chondrocytes prior to degeneration of cartilage, These result s support the hypothesis that the forces perceived by cells may dictat e their shape and then stimulate alterations in cellular biochemistry and matrix metabolism.