Physiologic weight-bearing and consolidation of new bone in a rat model of distraction osteogenesis.

To evaluate the effect of weight-bearing on consolidation of the regenerate in distraction osteogenesis, unilateral femoral lengthenings were performed in two groups of rats. In the first group (n = 19) unrestricted weight-bearing was permitted postoperatively, while in the second (n = 18) weight-bearing was prevented via a through-knee amputation. In both groups the distraction protocol involved a 3-day latency period, four daily 0.5-mm lengthenings, and 35 days of consolidation. Healing was evaluated with serial radiographs (days 0, 7, 14, 28, and 35) and at sacrifice with measurement of ash weight, quantitative histology, and mechanical testing. Histomorphometry revealed that the callus in the weight-bearing animals was significantly larger than in the non-weight-bearing animals, primarily due to increases in periosteal and interzone new bone; there was no significant increase in cartilage formation. Weight-bearing had no significant effect on the stiffness, strength, or mineral content of the regenerate. These findings suggest that weight-bearing may be capable of influencing consolidation of the regenerate in distraction osteogenesis. Additional studies will be required to determine the optimal loading for new bone formation.