Fracture repair during external fixation. Torsion tests of rabbit osteotomies.

Bone repair was studied in the rabbit tibiofibular bone after a midshaft transverse osteotomy stabilized by external fixation and heavy compression. Both subendosteal and subperiosteal callus formation with concomitant contact healing were observed within 3 weeks, and were further succeeded by subendosteal resorption and increased porosis resulting in atrophy of the cortical bone. Subjected to the torsion test, the bones exhibited restoration of strength within 3 weeks, with maximal energy absorption and elasticity at 6 weeks. The failure of the osteotomy in the torsion test, with radiographic visibility of the osteotomy, characterized the soft-tissue type of behavior of the bones. Hard-tissue like behaviour of the bones with resistance to torsion at the osteotomy site and radiographic obliteration of the osteotomy line occurred by 12 weeks, indicating complete union of the osteotomy. Our experiments demonstrate that elastic external fixation is preferable to the rigid compression plate.