Abstract
The amount of bone loss due to implant failure, loosening, or osteolysis can vary greatly and can have a major impact on reconstructive options during revision total knee arthroplasty. Massive bone loss can threaten ligamentous attachments in the vicinity of the knee and may require use of components with additional constraint to compensate for associated ligamentous instability. Classification of bone defects can be helpful in predicting the complexity of the reconstruction required and in facilitating preoperative planning and implant selection. One very helpful classification of bone loss associated with TKA is the Anderson Orthopaedic Research Institute (AORI) Bone Defect Classification System. This system provides the means to compare the location and extent of femoral and tibial bone loss encountered during revision surgery. In general, the higher grade defects (Type IIb or III) on both the femoral and tibial sides are more likely to require stemmed components, and may require the use of either structural graft or large augments to restore support for currently available modular revision components. Custom prostheses were previously utilised for massive defects of this sort, but more recently have been supplanted by revision TKA component systems with or without special metal augments or structural allograft.
Options for bone defect management are as follows: 1) fill with cement, 2) fill with cement supplemented by screws or K-wires, 3) Morsellised bone grafting (for smaller, especially contained cavitary defects), 4) Small segment structural bone graft, 5) Impaction grafting, 6) Large prosthetic augments (cones), 7) Massive structural allograft-prosthetic composites (APC), 8) Custom implants.
It is very helpful for revision surgeons to have a variety of reconstructive options available, even despite a well thought-out preoperative plan. Preoperative planning is important but the plan that results may require alteration during the course of the surgery to accommodate bone defects which are either less or more severe than thought pre-operatively, and to adjust to variable quality and extent of host bone remaining, as this provides the mechanical platform for the reconstruction. Maximising support on intact host bone is a fundamental principle to successful reconstruction and frequently requires extending fixation to the adjacent diaphysis.
Bone defect management during revision total knee arthroplasty can provide a wide range of challenges from relatively trivial problems with small defects manageable with cement or small amounts of cancellous graft to massive deficiencies that may defy reconstruction except with allograft prosthetic components or large segmental replacing tumor-type implants. The more common Type II deficiencies increasingly seen in the context of particulate driven osteolysis demand a wide range of implant and bone graft options so that an individualised reconstruction can be accomplished for that particular patient based on bone defect size, location, quality of bone remaining, ligamentous status, and anticipated patient demands.
