Fifty-eight rabbits were subjected to fracture and studied. Linear or segmental fractures at the junction of the middle and distal thirds of both radii of these animals were made. In all experimental ammals a Kirschner wire was inserted intrarnedullarly from the distal end of the right radius. The left radius was not fixed with any internal device and was used as the control side. Animals were sacarficed and studies made at 1 week, 10 days. 2, 3, 4,5, 8, 12, and 16 weeks. Radiography, microangiography, biochemical. and histological techniques were used.
The results were as follows:
1) Radiography:
The side with intramedullary fixation formed the periosteal callus earlier than the control side. Though callus formation appeared earlier in segmental fracture. complete healing was somewhat slower than it 11·as in animals with linear fracture.
2) Microangiography:
The nutrient artery was normal down to the fracture site on the control side. On the experimental side, the nutrient artery remained normal down to the most proximal point of the intramedually nail. As healing progressed, circulation increasedby development of now blood vessels at the cotex of the fracture site. This development was more pronounced on the experimental side.
3) Biochemistry:
A week after experimental fracture the alkaline phosphatase levels in the blood of the experimental animals increased to more than. twice that of the control animals. Serum phosphorus levels were one and one-half times higher than those of the control animals. No remarkable change was observed in serum calcium. There was no difference ill biochemical studies between linear and segmental fractures. After the first week, all blood chemistries studied returned to normal.
4) Histology:
Periosteal new bone formation was present at the end of one week. It was more advanced on the experimental side. At no time during the experiment did the intramedullary fixation side lag behind the control side in healing. In a few cases the healing on the side with fixation was significantly ahead of the control side. Linear fractures healedmore rapidly than segmental ones.
The conclusion of the experimental study is that:
1) In no case did the use of intramedullary fixation delay bony union.
2) In a few cases the use of iniramedullary fixation facilitated bony union.
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