Scattered mitosis in adult joint cartilage after partial chondrectomy. A histological, autoradiographical and biochemical study in rabbits.

Full-grown rabbits were operated on and subjected to total or partial chondrectomy of the cartilage in the patellar groove. In one group, only arthrotomy was performed in the control knee. The animals were killed at various times after the operation. Histologically, proliferation of the synovial cells at the joint margins, as well as osteoblastic activity, could be seen; later, osteophyte formation was observed. There were only minimal signs of degenerative changes in the cartilage. The biochemical investigation did not show any difference in the nucleic acids of the cartilage, either in relation to the time after the operation had taken place or in relation to the size of the trauma. In the knees where the cartilage was excised, thymidine-labelled chondrocytes were seen scattered in the joint. The number of labelled chondrocytes showed a rising tendency up to 14 days postoperatively, but no peak value was seen. In the arthrotomized knee joints, labelled chondrocytes were occassionally seen. It is possible that the scattered mitosis is the result of a reduction in the concentration of normal cell-specific inhibitors of mitosis, so-called chalones.