Biomechanical aspects of bone autografts and allografts.

The structural requirements of skeletal reconstruction should be included in the consideration of an appropriate type of bone graft, whether autogenous or allogeneic tissues are chosen. This analysis should include the nature of any fixation devices to be used, as well as characteristics of the host and donor bone. The mechanical properties and biomechanical response of the graft must be balanced against the type and magnitude of the load to which the graft will be subject. For example, the information presented here suggests that, from a biomechanical perspective, frozen bone would be better suited than freeze-dried bone when the graft is subject to large torsional loads or else the graft must be appropriately protected during incorporation by adequate internal fixation or external bracing. In a situation that is primarily subjected to compressive loads, however, freeze-dried grafts would be just as biomechanically sound. Thus, an understanding of the normal biomechanics of the anatomic region to be reconstructed is crucial. The mechanical properties of the graft are affected by preservation, storage, and sterilization. Incorporation and remodeling of the graft further alter its properties. These properties are, in turn, influenced by the host immune response as well as the local biomechanical environment. The influence of each of these factors is predictable. Obviously, there are numerous considerations in choosing approaches to skeletal reconstruction other than the mechanical issues discussed here. However, an understanding of the mechanical properties involved will help in optimizing the clinical success of these choices.