Allograft in Revision Total Knee Arthroplasty

Most defects encountered at the time of revision surgery can be reconstructed with augments and stems available in modern revision systems. Larger defects, however, may require replacement with custom implants or allograft bone. Morselized allograft is ideal for smaller contained defects and has even been successful in larger defects as long as the component achieves stability on the host rim bone. Structural allograft should be considered in large contained, segmental, and combined defects. When circumferential, deficiencies can be reconstructed with whole allograft composites. Medium-term survival is encouraging. Technique is critical. Rigid fixation between graft and host is essential. Components should be cemented to cut surfaces, as allograft has no biological potential for ingrowth. Press-fit diaphyseal stems share the load to protect grafts but may allow enough compressive force to promote union. Although radiographic resorption is reported in most series, it is unlikely that grafts revascularize. Retrieval studies in the knee and hip do not show revascularization or resorption. Graft collapse is probably due to trabecular fracture and the inability of the graft to repair and remodel. Many acetabular grafts failed early because they were not off-loaded. With the use of cages, survival has improved. Likewise, in the knee, stems reduce stress on grafts and protect against early fatigue failure.