Master Techniques in Orthopedic Surgery Knee CH21

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PART IV Revision Total Knee Arthroplasty ●● The trial components are removed and the final stem selections are determined depending on whether cemented or uncemented stems are to be used. The trials with the final stem trials are reinserted to ensure that component alignment and position is not affected. ●● Intraoperative radiographs may be obtained to verify appropriate sizing and alignment of the components before insertion of the final components. Insertion of the Femoral and Tibial Components ●● The real modular components are assembled with the appropriate stem extensions and standard metal augments. ●● With the new 3D printed titanium cones, bone graft is not needed to fill these voids because an intramedullary milling system is utilized. However, any remaining small gaps between the tantalum cones that have been previously impacted and the host are filled with either morcellized cancel- lous bone graft or demineralized bone matrix putty. This minimizes cement intrusion between the augment and host bone and, furthermore, may promote bone ingrowth around the entire periphery of the tantalum cone. ●● Finally, the real prosthetic components are cemented through the metaphyseal cones (Figure 21-19A and B). PEARLS AND PITFALLS ●● When preparing conical femoral or tibial bone defects with the high-speed burr to accept tantalum cone trials, unnecessary bone removal should be avoided. However, even with the plastic trial augments, rigorous impaction can produce a split in the bone. Therefore, the preparation process is a precision technique and the trials should be used frequently to assess fit. This fracture risk, in the experience of the authors, has been mitigated with the intramedullary reaming and milling system of the 3D printed titanium cones. ●● In most cases, the authors avoid the use of complete or partial wedges because of the shear stress on the interface between the augment and the cement mantle. Instead, we recommend converting a wedge-shaped defect to a step configuration to allow use of a block augment. This preparation can be performed either freehand, using the trial tray and block to mark the bone that must be removed, or with the use of an intramedullary cutting jig.

FIGURE 21-19. Final (A) anteroposterior and (B) lateral radiographs of a revision total knee arthroplasty with femoral and tibial three-dimensional printed titanium cones. A B