Abstract
Bone loss creates a challenge to achieving fixation in revision TKR. Failure to achieve metaphyseal fixation is associated with failure in revision TKR. In the absence of cancellous bone for cement fixation, metaphyseal augments placed without cement have shown promise in achieving fixation. First generation augments were modular solid titanium sleeves attached to a taper at the base of the core implant. The introduction of tantalum with its favorable mechanical qualities markedly increased the utility and utilization of metaphyseal augments, with positive reports. These are either large augments where the bone is prepared with a burr, or later small cones placed with a cannulated broaching technique. Both have solved real problems, the first being limited by the reproducibility of bone preparation, and the second with excellent reproducibility of bone preparation but limited diameters. Other highly porous titanium surfaces have broadened the choices.
Modern metaphyseal augments seek to add flexibility and options, specifically the use of offset stems. One tibial augment design features a reamed cone with a matching conical implant. Another option is based on an anatomic cone design with a single ream and a broached technique to optimise endosteal cortical bone contact. With each of these options, the augment can be placed wherever the remaining bone exists for fixation, even down to the metaphyseal-diaphyseal junction, and not limited to the area adjacent to the cut surface of bone. Once independent fixation is achieved, the intramedullary stem is cemented inside of it.
Modern femoral augments are designed to sit either in the epiphyseal region, or the metaphysis. Cannulated reaming systems allow for preparation of complex asymmetrical double cone implants at the epiphysis. Metaphyseal implants are designed anatomically to sit deeper in the femoral bone, and can manage larger bony defects. Each system has benefits and compromises, and together they comprise increasingly powerful alternatives to manage extensive bone loss.
