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pinned in place anteriorly (Fig. 9). It is important to line this jig up with the flat cut surface of the tibia to avoid edge loading. The jig is rotated to the posterior aspect of the finishing guide until it is collinear with the proximal tibial cut and headed, threaded long pins are placed to secure the cutting block. Both peg holes are now drilled to a positive stop on the drill. The chamfer and posterior femoral cuts should be made sequentially through the guide. The chamfer cut must be exact and often requires removal of 1 pin and placing it in a different hole. We recommend cutting the posterior femoral cuts before the chamfer cut. The appropriate femoral trial component is placed on the prepared femoral condyle (Fig. 10). A headed gold pin locks the jig in place and the posterior pins are also placed. We have found that in order to avoid edge loading, we bias the femoral sizer toward the notch. With all cuts complete, a smooth, laminar spreader is placed and 1.27-cm (0.5-inch) curved osteotome is used to remove all posterior osteophytes to gain high flexion. Any remaining meniscus is excised and the posterior joint is inspected for any loose bodies. TRIALING COMPONENTS AND BALANCING GAPS The key to a successful UKA is a well-aligned prosthesis, restoring the mechanical axis to neutral (or slight undercorrection), and having appropriate ligamentous tension in both flexion and extension without overstuffing the prosthesis. Overloading the contralateral compartment can accelerate degenerative changes.46 The use of the spacer guide minimizes this risk by ensuring laxity in the operative compartment, as discussed earlier. The fit of the tibial trials is best evaluated with the knee in 90 of flexion and slight external rotation. The use of the largest tibial tray possible without overhang, matching the implant size to the peripheral cortical bone, provides the most support for the implant (Fig. 11). Occasionally, the sagittal cut may need to be repeated, moving toward the notch to accommodate the larger tibial tray. Once the trial tibial tray is inserted, rotational alignment is confirmed when the insertion handle is 90 to the coronal axis of the proximal tibia and no overhang is noted. Fig. 9. (A) Femoral cutting block in place. It is important to appropriately size the femoral cutting block so there is no overhang. (B) Proper sizing of the femoral jig. 96 Dunn et al A curved device is included in the set to feel around the back of the knee with the sizing guide to ensure that the correct tibial prosthesis is selected. The tibial keel is prepared with the provided keel punch and then inserted (Fig. 12A). It is important when creating this trough to first set it flush with the tibial cut surface, then send it posteriorly with good coverage, before drilling the 2, 20-angled posterior tibial holes (see Fig. 12B). The trial femoral component and the trial polyethylene component are then inserted and the patellar retractor is removed. After the trial components are inserted, the flexion extension gaps and tracking are evaluated. The knee is moved through its full ROM without the tension gauge to assess tracking between the femoral and tibial components. The tension gauge is then inserted, with the knee flexed to 90. The tension gauge should slip in and out of the joint with 2 fingers and slight resistance without movement of the tibial trial on the 2-mm side. Movement of the tibial trial is an indication that the flexion gap may be too tight. This step should also be repeated with the knee in full extension. If the tibial trial moves when in extension, the extension gap may be too tight. At this point, necessary adjustments should be made to balance the gaps and properly align the components. Fig. 10. Femoral trial sizing is completed before the trial component is placed on the prepared femoral surface. Fig. 11. Templates to find the largest tibial tray are completed. UKA: Intramedullary Technique 97 FINAL PREPARATION AND CEMENTING OF FINAL IMPLANTS In final preparation for implant placement, the prepared bony surfaces are copiously irrigated with antibiotic solutions and the joint is reinspected for debris. The bony surfaces are dried and a 10.2-cm 8-inch) sponge held by a Z retractor is placed in the posterior aspect of the joint in addition to a thrombin spray. The cement should be compressed into the tibia with a finger or a ganglion knife, making sure not to place excessive cement posteriorly. Excess cement is difficult to remove after the implants are in place. We advise placing a small amount of cement only on the posterior aspect of the prosthesis and the anterior section of the tibia. The final tibial component is then inserted and impacted into place. A small, curved curette and a knife are used to remove excess cement from the posterior aspect of the joint. The process is then repeated with the femoral component, and the trial polyethylene component is placed (Fig. 13). Fig. 12. (A) The tibial keel is placed with an appropriate tibial tray to finalize preparation of the tibial surface. (B) The cut tibial surface is completed, and the posterior tibial holes are prepared. Fig. 13. The tibia is cemented in place, and the femoral surface is prepared with cement to accept the real prosthesis. 98 Dunn et al The leg is moved into extension to compress the components while the cement cures. The cement is monitored, and when appropriate, the previously packed sponge in
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