Master Techniques in Orthopedic Surgery Knee CH21

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PART IV Revision Total Knee Arthroplasty Therefore, although radiographs remain an important tool for evaluating limb alignment and component positioning in the coronal and sagittal planes, additional studies should be considered for evaluating bone loss, especially when osteolysis is suspected. Evaluation of radiographs and CT or MRI scans preoperatively is especially important if revision surgery is performed in centers where a complete array of porous metaphyseal cones and revision knee prostheses are not immediately available. This allows the surgeon to procure the prosthetic and augment options that may be required. TECHNIQUE In this section, we address in a stepwise manner the use of both tantalum and 3D printed titanium cons for managing AORI type II and III bone defects. Evaluation of Bone Loss ●● After obtaining adequate surgical exposure, the original components are removed. ●● Loose cement and bone is debrided. ●● Classification of femoral and tibial bone loss is performed according to the previously described AORI system. ●● A tentative reconstructive plan is formulated. ●● The tibial surface is freshened with a saw to create a flat surface. ●● The femoral and tibial canals must be opened up and reamed to size the appropriate stem extensions. Preparation for Tantalum Cones ●● In some cases, only a tibial or femoral cone is required. However, when both the femur and tibia have large bone defects that require reconstruction, start with reconstruction of the tibia. ●● A variety of full femoral and tibial tantalum cones, as well as asymmetric stepped tibial designs, are available. ●● A trial augment is used to size the defect. The trial augment that best fits the bone defect and produces the optimal peripheral contact with the remaining host bone is selected. ●● In most cases, the bone defect does not exactly match one of the available sizes. As such, a high-speed burr can be used to contour the host bone or augment itself. New metaphyseal broaches that aid in metaphyseal preparation, especially with smaller, contained defects, are also now available. ●● Once the tibial trial has a good press fit with maximal peripheral contact, the real cone can be selected and impacted in place. ●● The femur can be prepared in a similar manner if required. Preparation for 3D Printed Titanium Cones ●● Similar to tantalum cones, we prefer to reconstruct the tibia first. ●● A variety of symmetric and lobe-shaped 3D printed titanium tibial cones are designed to be used in type I through III bone defect. ●● Symmetric cones are used in type I and IIA bone defects, whereas lobe-shaped cones are designed to be used in type IIB and III bone defects. ●● The tibial cut is freshened either with an intramedullary alignment guide or freehand. ●● An appropriately sized tibial component is selected, as well as stem and metal augments if needed. It is our preference to utilize a mid-length cemented stem. ●● The rotation of the tibial component is established in line with the tibial crest, and corresponding keel and stem preparation is completed. ●● Either a reamer or stem trial (Figure 21-10) is then placed in the intramedullary canal after the canal is reamed to a diameter where the reamer is stable within the canal. ●● A central symmetric reamer is then utilized to a depth that corresponds to the size of the 3D printed titanium cone (Figure 21-11). ●● The trial (Figure 21-12A), and real 3D printed titanium tibial cone (Figure 21-12B), is then inserted with an impactor. The score mark is aligned with the tibial crest. ●● The femoral cones are based on a bilobed design that allows the lobes to bottom out at the junction of the metaphysis and diaphysis (Figure 21-13). This prevents longitudinal fractures of the femur.