Abstract
Block allografts traditionally have been used for massive bone deficiencies, but their complication rates are high, and the destructive effects of allograft rejection can limit their long-term success. Large segments of allograft also heal slowly, are never replaced by new bone, and weaken as the ossification and vascularisation front proceeds. In contrast, morselised allograft has proven structurally reliable for both small and large defects while supporting new bone formation. Morsels that are 1 cm in diameter maintain their integrity long enough to act as a substrate for new bone formation. Morsels less than 0.5 to 1 cm in diameter tend to be resorbed while those larger than 1 cm incorporate slowly, if ever, and tend to collapse.
Rejection can be a major problem with allograft because marrow is immunogenic. However, marrow elements can be thoroughly removed from morselised allograft to prevent the inflammatory response and loss of graft and to capitalise on the osteoconductive potential of the demineralised bone and autologous marrow. The allograft acts as scaffolding for new bone growth, and although it is not osteoinductive, demineralised bone (mildly osteoinductive) and bone marrow aspirate (highly osteoinductive) can be added to the allograft to enhance bone formation. The surrounding bone structure supplies most of the osteoinductive activity because metaphyseal bone has a rich blood supply and maintains the capacity to heal even after repeated failed arthroplasty.
Grafting preparation and placement: Fresh-frozen cancellous allograft in morsels measuring 0.5 to 1 cm in diameter is soaked for five to ten minutes in normal saline solution that contains polymyxin 500,000 units, bacitracin 50,000 units, and cephazolin 1 g/l. The fluid is removed and 10 cm3 of powdered demineralised cancellous bone is added to each 30 cm3 of the cancellous morsels. Bone fragments and diaphyseal reamings are added to improve the osteoinductive potential. This mixture is packed into the bone defects, then the implants are impacted so as to seat on the remnant of viable bone while compacting the morselised bone graft.
The abstracts were prepared by Mrs Dorothy L. Granchi, Course Coordinator. Correspondence should be addressed to her at PMB 295, 8000 Plaza Boulevard, Mentor, Ohio 44060, USA.
