Changes in the AO/ASIF principles and methods

Abstract

Early AO/ASIF principles and methods emphasized the operative treatment of fractures, the mechanical aspects of internal fixation and the absolute stability of all fragments. Absolute stability was thought necessary to make internal fixation sufficiently strong to allow immediate movement of joints and partial loading of the bones. Investigation revealed that osteoporosis or accelerated Haversian remodelling associated with plating was not the result of stress protection but the result of damage to the blood supply to the bone. Similarly accelerated Haversian remodelling was noted along the endosteum of long bones with intramedullary nailing. This remodelling paralleled the distribution of dead bone brought about by reaming and nailing. Primary bone healing is histologically identical to remodelling and would be more appropriately regarded as accelerated remodelling of the dead bone at the fracture under conditions of absolute stability. Under conditions of relative stability only living bone will unite because only living bone is capable of overcoming motion and bringing about stability by the formation of callus. The recognition that implants and the manipulation of fragments devitalize bone and can interfere with union has brought about a shift from the quest for absolute stability to the emphasis on the preservation of the blood supply and to the recognition of the biological requirements of the different segments of bone. Thus, fractures involving end segments, such as articular fractures, require anatomical reduction and absolute stability for union and regeneration of articular cartilage, whereas diaphyseal fractures require only relative stability with restoration of length, axial alignment, and rotation for union and for the full return of function. Thus, diaphyseal fractures of long bones are best treated with locked intramedullary nailing whereas end segment fractures require lag screw fixation and plating. Fractures of the forearm are an exception. The anatomical relationship of the two bones makes them behave as a .joint. Therefore, they require an anatomical reduction for full return of function. Where intramedullary nailing is contraindicated methods of indirect reduction and bridge plating have been developed to minimize devitalization of bone. The recent recognition that manipulations of the medullary canal such as reaming and nailing may seriously compromise pulmonary function has led to a reappraisal of the intramedullary nailing of long bone fractures in polytrauma patients with pulmonary contusion and a high ISS. Therefore, there are a large number of specific indications for absolute stability and plating, and consequently a great need to develop new plates and new methods of their application which would minimize the damage to the blood supply to the bone and promote union.