Cementless fixation issues in revision total knee arthroplasty

Abstract

Although massive solid allografts can be expected to vascularize and form new bone, variable amounts of replacement as well as collapse and necrosis may be prominent features of these large block allografts. Immunocompatibility seems to be an important factor in allograft healing and incorporation. Large block allograft of the acetabulum appears to be more likely to succeed if autograft is used. Rejection appears to be a significant factor in survival of large allografts. Although bone itself is not highly immunogenic, the role of marrow elements in the cancellous bone graft may be crucial. When possible, marrow contents should be washed carefully from the interstices of cancellous bone to remove cellular elements that do not contribute to osteoinduction but do produce an inflammatory immune response that can compromise healing and bone formation. Washing and soaking the components in antibiotic solution has the additional benefit of making available a reservoir of antibiotic that is released slowly during the postoperative period. Morcellized cancellous bone, rather than finely ground bone which tends to be destroyed by phagocytosis, is the best available choice for reconstructing large volumes of deficient bone stock. Fixation is completely dependent on the existing bone, so that massive defects must be protected until sufficient rigidity develops in the grafted material to allow sharing of weightbearing loads. Clinical experience has shown that migration of the tibial component after reconstruction with morcellized allograft is rare during the first 2 to 5 years after surgery (Fig. 8). These results are surprising in light of reported experience with structural allografts of the acetabulum. Jasty and Harris reported loosening of acetabular components after 4 years in 32% of their cases. The biologic behavior of morcellized allograft differs from that of block allograft, however. Vascularization and ossification are rapid and a permanent, competent loadbearing structure is achieved by filling large deficient areas. The biologic response obtained with the correct technique appears to be early and vigorous. It does not seem likely that progressive collapse would occur after remodeling and healing have been established (Fig. 9). Bone graft handling probably is crucial to the success of grafting of the knee. Antibiotic soaking and washing, removal of bone marrow, and adequate support of the implants are all necessary factors for consistent success of this technique. The results of this salvage procedure have been encouraging. The grafting technique appears to provide long-term support for the implants, so that repeat revision is unlikely.