Influence of the fibula on growth of the rat tibia.

To investigate the effect of the fibula on growth of the tibia in the rat, (1) a sleeve of periosteum was removed from the middle third of the tibia, (2) a length of the fibula was excised, or (3) a sleeve of periosteum was removed from the middle third of the tibia and a length of fibula was also excised. Over a 14 wk experimental period subsequent tibial bone growth was measured on radiographs and compared with unoperated contralateral control tibiae. Procedure (1) had no effect on growth, (2) resulted in 4.2% overgrowth and (3) produced 19.7% overgrowth compared with control tibiae. The failure of overgrowth after periosteal resection from the middle third of the rat tibia argues against the vascular response theory in relation to bone overgrowth. The longitudinal overgrowth after procedure (2) and its further accentuation by procedure (3) suggests that the fibula influences tibial bone growth by exerting a mechanical restraint on it, which is reciprocal to the restraining influence of the tibial periosteum. Overgrowth appears to be facilitated by decompression of the cartilage growth plate of the rat tibia when a sleeve of the periosteum is removed from it, and this suggests a mechanical relationship between the fibrous periosteum and the cartilage growth plate of the tibia. It is concluded that the fibula plays a reciprocal role in regulating tibial bone growth in the rat.