Establishment of a non-union model using muscle interposition without osteotomy in rats.

Many attempts have described a standard experimental model for fracture non-union in laboratory conditions, but the majority of them produced after an experimental osteotomy, so it is different from clinical disturbed fracture healing. The purpose of this study is to establish a standard method for producing fracture non-union with only muscle interposed into the fracture site in rats. Bilateral tibial fractures were made in forty-eight male Wister rats by three point bending and we surgically interposed the distal end of the tibialis anterior muscle into the fracture site. They were sacrificed at 1, 2, 3, 6, 12, 24, 48, and 96 weeks after fracture. The rentgenograms were obtained, and the fractured tibias were harvested in each time period and investigated histologically and immunohistochemically. The rentgenogram at six weeks, in the non-union rats, showed abundant callus at each end of the fracture fragments, but no bridging callus. The histological finding with hematoxylin and eosin, at this point, shows no bridging soft callus, and small isolated regions of cartilage were observed only where the bone was not covered by the muscle. The proliferating cell nuclear antibody immunostaining which is associated with cell proliferation was abruptly lost in chondrocytes at two weeks. This early disappearance of chondrocytes without endochondral ossification may be a significant etiological factor in the development of a non-union. This non-union model is technically simple and reproducible, and dose not require periosteal stripping or surgical osteotomy to produce an artificial bone gap.