Application of tissue isolation technique and mechanical mobilization in developing non-union models of the rabbit tibial diaphysis

Aim: To evaluate the effect of tissue isolation technique and mechanical mobilization in building atrophic and hypertrophic non-union model of tibial diaphysis in rabbits. Methods: Twelve New Zealand white rabbits of 18 weeks with a body weight of 3 to 4.5 kg were randomly divided into two treatment groups. In Group A, the tissue isolation technique was applied so as to establish atrophic non-union model. After a transverse osteotomy of the middle third of the tibial shaft was performed, the periosteum on either side of fracture site was excised and the marrow was removed by curettage. The either end of the fracture was covered by 1 cm silastic tube and the fracture was fixed with a Hoffman unilateral external fixator. The fracture gap was displaced to 2 mm. Eight weeks later, the silastic tube was removed. In Group B, mechanical mobilization was used to produce a hypertrophic non-union model. The surgery procedure is similar to Group A. However, the silastic tube was not placed over the fracture end and a K-wire was introduced as intramedullary nail for loose fixation. The passive motion of fracture site was performed 200 times/d for one month. The non-union was evaluated using plain radiograph. Results: None of the rabbits were showed to have healed at the operated site following the removal of the silastic tubes after an interval of 4 weeks in all rabbits of Group A. The radiographs displayed well-formed atrophic non-union. In Group B, after 6 weeks, all rabbits were found that fracture healing was delayed, with some also having deformity. A large number of hypertrophied callus at the fracture site occurred. Conclusion: The tissue isolation technique seems to be an effective method to develop the atrophic non-union model of the rabbit tibial diaphysis. Using passive mechanical mobilization to build a hypertrophic non-union model in rabbits needs further studies.