Biomechanics of healed experimental fractures

Biomechanical properties of osteotomies and physiologically fractured canine femurs fixed with six-hole stainless steel AO/DCP plates (Synthes: Paoli, PA) were investigated with torsional loading 12 weeks postoperatively and were compared. Biomechanical evaluation of fracture healing with compression plate fixation requires a well controlled fracture creation technique which should reflect closely the natural process. Osteotomy has been suspected of creating ;local bone necrosis, a segmental defect, and subsequent healing patterns which do not mimic those following a more physiologic fracture. Two fracture techniques were compared in the mid-diaphyseal canine femur. An osteotomy was created in one limb and stabilized with a dynamic compression plate, while the contralateral limb was fractured physiologically utilizing four-point bending (modified technique of Ashhurst et al.) and also stabilized with a dynamic compression plate. Comminution developed in one animal during the four-point bending fracture creation technique and nonunion developed in an animal following osteotomy. Following sacrifice at three months, dynamic torsion testing demonstrated no statistical difference in mean torque to failure (osteotomy = 27.7, SD 9.4 N m; physiologic fracture = 28.4, SD 5.0 N m). Stiffness, rotation to failure, and energy to failure were also analysed and demonstrated no statistical difference.