Biomechanics of Internal Fixation Devices

The internal fixation of fractures has evolved in recent decades with a change of emphasis from mechanical to biological priorities. More flexible fixation should encourage the formation of callus while less precise, indirect reduction will reduce operative trauma. This approach is described as'biological internal fixation.Internal fixation with a plate aimed at absolute stability to avoid micromovement which could result in loosening of the implant and a delay in healing. The new technique of internal fixation, however, seems to tolerate and even require some degree of mobility of the interface of the fracture. The concept of biological internal fixation is still developing. The biomechanical aspects principally address the degree of instability which may be tolerated by fracture healing under different biological conditions.