Bone grafts

A graft is living tissue that is transplanted to another site either within the same individual or into another individual to repair a defect. An impl ant is a nonviable material placed in a living system. Implants are compose d of bone cement, frozen cortical bone, metal, or ceramic material. Early g rafts were structurally important for mechanical stability, but their use h as evolved to include the stimulation and enhancement of bone in response t o injury. Knowledge of the terminology defining bone grafting is necessary to understand the indications, contraindications, functions, and biological repair of various types of bone grafts. Bone grafts are named according to their site of origin and composition. An autograft (autogenous) is tissue that is harvested from a donor site and t ransplanted to a recipient site within the same individual. This type of gr aft is histocompatible with the host's immune system and carries little ris k of disease transmission. An allograft (allologous, allogenic) is tissue t hat is transplanted from one individual to another of the same species. An alloimplant is allograft material such as cortical bone that has been prese rved by freezing, freeze-drying, autoclaving, chemical preservation, or irr adiation, so that it is no longer living tissue and does not stimulate an i mmune response. A xenograft (xenogenic) is tissue transplanted from one ind ividual of one species to another of a different species. Different compositions include cancellous, cortical, corticocancellous, com posite, and osteochondral grafts. Cancellous grafts consist of highly cellu lar trabecular bone that is harvested from marrow cavities associated with the metaphyseal regions of long bones. These grafts enhance bony healing bu t do not provide immediate mechanical or structural support for the bone. C ortical grafts consist of dense outer cortical bone that provides structura l support as well as scaffolding for the ingrowth of new bone. Corticocance llous grafts are a mixture of both cortical and cancellous bone. Composite grafts are a combination of fresh cancellous bone used with preserved alloi mplants. Osteochondral grafts include articular cartilage as well as bone. A fresh graft is harvested at the time of use, and a preserved graft is har vested prior to use, sterilized, and stored. The most commonly used methods of sterilization include chemical sterilization with ethylene oxide, freez ing, and irradiation. Vascularized grafts are harvested with blood vessels intact and are anastomosed at the recipient site. With a free graft, the bl ood supply is no longer intact, and vascularization occurs, with the angiog enesis originating at the host site.