Master Techniques in Orthopedic Surgery Knee CH21

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21 Managing Bone Loss with Metaphyseal Cones

FIGURE 21-3. Type III bone loss has deficient metaphyseal bone that compromises a major portion of either condyle or plateau.

Standardmetal augments are augments that, regardless of size, attach directly to the body of the prosthesis with cement, snap or taper fit, or screw fixation. They may be composed of titanium, cobalt chrome, or tantalum. These augments are system specific and available in a variety of sizes and styles. Femoral aug- ments, typically blocks that are 5 to 20 mm thick, attach to the distal or posterior condyles of the prosthesis (Figure 21-4). Tibial augments include blocks, and partial or full wedges that attach to the undersurface of the tibial tray (Figures 21-5 and 21-6). These tibial augments also replace up to 15 to 20 mm of bone loss. In addition, sleeve augments are available in some systems for the tibia and femur (Figure 21-7). These sleeve augments insert over the stem of a revision component and are designed to fill metaphyseal defects. Porous metaphyseal cones do not attach to the prosthesis, but instead are impacted directly into large areas of femoral or tibial metaphyseal bone loss. Currently available options include porous metaphyseal tantalum cones (Trabecular Metal [TM]; Zimmer-Biomet; Warsaw, IN) (Figure 21-8), and porous titanium cones that are either three-dimensional (3D) printed (Tritanium; Stryker; Mahwah, NJ) (Figure 21-9) or produced via a heating process using a mixture of titanium powder that contains other binding agents (Zimmer-Biomet). These cone augments allow the restoration of a stable foundation upon which the prosthesis, with or without additional standard augments, can be supported. It is this ability to use these augments independently of the prosthesis, as a structural bone graft substitute, that differentiates porous metaphyseal cones from other metaphyseal filling metal augments.

FIGURE 21-4. Revision femoral component demonstrating metal augments on the distal and posterior aspects of the femur. The femoral augments are composed of tantalum and are attached via screw fixation.

FIGURE 21-5. Revision tibial component demonstrating metal augments that are cemented to the tray.