Mandible reconstruction and autogenous frozen bone graft: Experimental study on rats

The aim of this study was to evaluate the biological behaviour of a frozen bone graft in orthotopic and heterotopic sites in the rat. The previous exp erimental study on this subject was published 25 years ago without sufficie nt detail about the histology and comparison between the orthotopic and ect opic sites. Therefore, being very important for future clinical application , we decided to evaluate the frozen bone graft using rats. The procedure wa s performed on two groups of five rats each (Charles River). After wide dis section of the inferior border of the mandible from the surrounding muscle, an inferior segmental resection 4 mm in length was performed, taking care not to fracture the superior part and to maintain mucosal integrity. This s egment was placed in liquid nitrogen for two periods of 10 minutes each wit h a third period to allow it to reach room temperature. In the first group (A), the frozen segment was placed ectopically in a gluteal muscle pocket, and in the second group (B), the frozen bone was fixed in the same position in the same mandible. After 1 month of follow-up, the animals were killed, the bone graft was removed, and histology was performed. Results were cons istent in both groups. In group A, the segment was sur rounded by strong in flammatory reaction, with no vital cells or bone cells, but some vascular p enetration. We concluded that there was no bone deposition and no bone reha bitation. in group B, the initial segment was strongly fixed to the remaini ng mandible, there was an increase of the macroscopic dimension that parall eled the increase in the dimension of the remaining mandible and the growth of the animal. The cortical part had thinned down, the medullary part pres ented signs of bone deposition as well as bone resorption and vascular pene tration. The periosteum from the adjacent normal mandible was growing and c overing the frozen bone graft, offering additional stimulus to the bone dep osition. In conclusion, the frozen bone graft acts as a normal bone graft. It needs to be placed in contact with vascularised bone and surrounded by w ell vascularised soft tissue to allow deposition of new bone. If the frozen graft is placed ectopically, it will be surrounded by chronic inflammatory reaction with no bone deposition. (C) 2001 Wiley-Liss, Inc.