Revision, and complicated primary total knee arthroplasty (TKA), may present with significant structural bony defects. Allograft offers blocks of material that can be shaped to the defect. The opportunity to gain a biological bond may theoretically enhance loading conditions and enhance any subsequent surgery. However, the biomechanical and biological issues of immune response, infection, graft incorporation, resorption, and load transfer render allografting a powerful but problematic technology.