Abstract
Metaphyseal bone loss is common with revision total knee arthroplasty (TKA). The causes of bone loss include: osteolysis, loosening, infection, iatrogenic or a combination. Small defects can be treated with screws and cement, bone graft, and non-porous metal wedges or blocks. Large defects can be treated with bulk structural allograft, impaction grafting, or highly porous metal cones or augments. The AORI classification of bone loss in revision TKA is very helpful with preoperative planning. Type 1 defects do not require augments or graft—use revision components with stems. Type 2 defects should be treated with non-porous metal augments—wedges or blocks. Type 3 defects require a bulk structural allograft or large highly porous metal cone. Trabecular metal (TM) metaphyseal cones are a unique solution for large bone defects. There are both femoral (full or partial) and tibial (full or stepped) TM cones available. These cones substitute for bone loss, improve metaphyseal fixation, help correct malalignment, restore joint line, and perhaps, permit use of a shorter stem. The technique for these cones involve sculpturing of the remaining bone with a high speed burr and rasp, followed by press-fit of the cone into the remaining metaphyseal bone. The interface is sealed with bone graft and putty. The fixation and osteoconductive properties of the outer surface allow ingrowth and hopefully long term biologic fixation. The revision knee component is then cemented into the porous cone inner surface, which provides superior fixation compared to deficient metaphyseal bone. The advantages of the TM cone compared to allograft include: technically easier; biologic fixation; no resorption; and (?) lower risk of infection. The disadvantages include: difficult extraction and relatively short-term follow-up. The author has reported the results of 33 TM cones (9 femoral, 24 tibial) implanted in 27 revision cases at 2–5.7 years follow-up. One knee (2 cones) was removed for infection. All but one cone showed osseointegration. TM cones are a promising method for the reconstruction of large bone defects in revision TKA.
