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 t he tibia, (2) a length of the fibula was excised, or (3) a sleeve of p eriosteum was removed from the middle third of the tibia and a length of fibula was also excised. Over a 14 wk experimental period subsequen t tibial bone growth was measured on radiographs and compared with uno perated contralateral control tibiae. Procedure (1) had no effect on g rowth, (2) resulted in 4.2% overgrowth and (3) produced 19.7% overgrow th compared with control tibiae. The failure of overgrowth after perio steal resection from the middle third of the rat tibia argues against the vascular response theory in relation to bone overgrowth. The longi tudinal 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 r estraining influence of the tibial periosteum. Overgrowth appears to b e facilitated by decompression of the cartilage growth plate of the ra t tibia when a sleeve of the periosteum is removed from it, and this s uggests a mechanical relationship between the fibrous periosteum and t he cartilage growth plate of the tibia. It is concluded that the fibul a plays a reciprocal role in regulating tibial bone growth in the rat.