Mitosis of chondrocytes in normal adult joint cartilage.

Local traumatization of adult rabbit joint cartilage induces mitosis of chondrocytes not only in the cartilage of traumatized joints but also of the normal cartilage of sham-operated or unoperated-on control joints. All the cartilage of the patella groove of the femur of adult rabbits was excised while the other knee underwent arthrotomy or was left intact. Radioactive thymidine and autoradiographic technique demonstrated that labeled chondrocytes appeared not only around the excised cartilage but also scattered in the tibia and femoral condyles. Scattered mitoses of chondrocytes were also seen in the normal cartilage of sham-operated and unoperated-on control knee joints. The peak of labeling appeared two weeks after operation, and the operation did not result in development of osteoarthritis. Whether the stimulation of chondrocytes is due to a decrease in cell-growth-inhibiting factor or to a liberation of stimulating substances is not known.