Growth of the ribs at the costochondral junction in the rat.

The in situ growth of the ribs at the costochondral junction was examined by 2 methods. In the first, 3 threads were tied around the 5th, 6th or 7th ribs of 20-d-old rats. The first thread was located around the bony part of the rib close to the costochondral junction, the second around the cartilaginous part the same distance away from the junction, and the third also around the cartilaginous part but further away. The distances between the threads were measured at 20 and 40 d and were found to have increased considerably. In the second part, an immunohistochemical method using bromodeoxyuridine was employed to detect proliferating cells at the costochondral junction. The most active cell proliferation was observed in the proliferative zone, but mitoses were also noticed in the germinative zone. The results provide further evidence that the growth potential of costochondral grafts used in reconstructive surgery is related to the length of their cartilaginous portion.