Abstract
The management of bone loss in revision total knee replacement (TKA) remains a challenge. To accomplish the goals of revision TKA, the surgeon needs to choose the appropriate implant design to “fix the problem,” achieve proper component placement and alignment, and obtain robust short- and long-term fixation. Proper identification and classification of the extent of bone loss and deformity will aid in preoperative planning. Extensive bone loss may be due to progressive osteolysis (a mechanism of failure), or as a result of intraoperative component removal. The Anderson Orthopaedic Research Institute (AORI) is a useful classification system that individually describes femoral and tibial defects by the appearance, severity, and location of bone defects. This system provides a guideline to treatment and enables preoperative planning on radiographs.
In Type 1 defects, femoral and tibial defects are characterised by minor contained deficiencies at the bone-implant interface. Metaphyseal bone is intact and the integrity of the joint line is not compromised. In this scenario, the best reconstruction option is to increase the thickness of bone resection and to fill the defect with cancellous bone graft or cement. Type 2 defects are characterised by deficient metaphyseal bone involving one or more femoral condyle(s) or tibial plateau(s). The peripheral rim of cortical bone may be intact or partially compromised, and the joint line is abnormal. Reconstruction options for a Type 2A defect include impaction bone grafting, cement, or more commonly, prosthetic augmentation (e.g. sleeves, augments or wedges). In Type 2B defects, metaphyseal bone of both femoral condyles or both tibial plateaus is deficient. The peripheral rim of cortical bone may be intact or partially compromised, and the joint line is abnormal. Options for a Type 2B defect include impaction grafting, bulk structural allograft, prosthetic augmentation, metaphyseal sleeves (in some cases), or metaphyseal cones. Finally, in the presence of a Type 3 deficiency, both metaphyseal and cortical bone is deficient and there is partial or complete disruption of the collateral ligament attachments. In this case, the most commonly used reconstruction options include hinged implants or megaprostheses with or without bulk structural allograft, prosthetic augmentation, and/or metaphyseal/diaphyseal sleeves or cones.
Today, we are fortunate to have a wide variety of options available to aid in reconstruction of a revision TKA with massive bone loss. Historically, use of cement, bone grafting, or use of a tumor-type or hinged implant were considered the main options for reconstruction. The development and adoption of highly porous sleeves and cones has given the surgeon a new and potentially more durable option for reconstruction of previously difficult to treat defects. Using radiographs and computed tomography, surgeons are able to preoperatively classify bone loss and anticipate a reconstruction plan based upon the classification; however, it is always important to have several back-up options on hand during revision surgery in the event bone loss is worse than expected.
