There are a variety of options for filling defects during revision total knee arthroplasty: cement with or without screws, structural or morselized allograft, highly porous cones and sleeves, massive bone allograft or megaprostheses. Our goal is to describe the techniques for these procedures and their indications. Any necrotic bone, fibrous tissue or granulomas must be excised, and the bone freshened. The height of the joint line must be restored using trial components stabilized by stems. The defect is the space between the bone and each of the two components. Whether contained or not, it can be evaluated using the AORI classification. Cement alone or supplemented with screws, which is pressurized to penetrate the bone, is now only used in small defects less than 10mm in diameter, especially contained one. It is preferable to use morselized compacted bone graft instead. Augments are used to fill AORI type 2 defects less than 10 mm deep in a condyle. They can also be used to position the femoral component and sometimes the tibial one. For type 2 and 3 defects, bone allografts aim to reconstruct the skeleton. They can be used as trimmed fragments, as described by Engh who did hemispheric reaming to embed a femoral head into the defect. One can also compact or pack morselized bone graft around a stem. These reconstruction procedures are long and difficult. They are being done less and less since porous cones and sleeves were introduced, which are impacted after bone preparation. These sterile components are secured to the stem either mechanically or with cement, saving time. Once in place, bone grows into them. They provide metaphyseal anchoring that helps to reduce the stem's length. When the epiphysis is nearly all gone, the choices are a massive bone allograft or a megaprosthesis, although both have a high risk of infection and mechanical failure. The allograft must be trimmed to restore the height of the joint line and achieve a stable connection with the host bone. A long stem, always cemented into the allograft, is essential. In older patients, a megaprothesis is simpler to use and faster. The femur is better suited to massive reconstruction than the tibia, where coverage must be ensured along with extensor mechanism continuity.

V; expert opinion.