Chondrocyte ultrastructure in exercise and experimental osteoarthrosis. A stereologic morphometric study of articular cartilage of young rabbits using transmission electron microscopy.

The effects of physical exercise (running) and immobilization (splinting) on chondrocyte ultrastructure were studied in the knee joint articular cartilage of 24 young rabbits. Synthetic activity of the chondrocytes was quantified by measuring the amount of rough endoplasmic reticulum (RER) from electron micrographs using a sterologic point-counting method. Extra loading of the joint by running, or by increased weight-bearing after splinting of the contralateral limb, caused a 20% and 30% increment of RER in the middle and deep zones of the cartilage, respectively, while immobilization decreased the amount of RER by 30% in the superficial zone. Some attempts to repair and regenerate were observed, especially in the deep zone of articular cartilage. Hypertrophy of cells and organelles, and cell replication were considered as signs of reparative processes. The accumulation of fine intracytoplasmic filaments (FIF) in chondrocytes, regarded as a sign of cell degeneration, was reduced in the exercise group. FIF also decreased in the deep zone chondrocytes of the immobilized group, which could be indicative of improved or retained viability of the chondrocytes.