Master Techniques in Orthopedic Surgery Knee CH27
PART V Alternatives to Total Knee Arthroplasty include 3-ft weight-bearing anteroposterior hip-to-ankle, lateral, and sunrise patellar views as well as varus- and valgus-stress views. Lateral radiographs show the orientation of the medial condyle on the tibial plateau and allow evaluation of the competency of ACL and extent of posterior involvement. A varus-stress view confirms the presence of bone-on-bone arthritis, whereas a valgus-stress view ensures a correction of the deformity and maintenance of the lateral joint space. Templating of the femur is necessary to choose the size of the femoral component. TECHNIQUE The patient is placed supine on the operating table, with the operative extremity restrained in an appropriate leg holder to ensure that full flexion can be obtained after draping. The hip should be abducted to 30° with a thigh support. Ensure the knee can be flexed to 120° with thigh support not impinging on popliteal fossa. A thigh tourniquet is placed on the operative extremity and the appropriate intravenous antibiotics are given. The center of the femoral head should be marked at the midpoint between the pubic tubercle and the anterior superior iliac spine (ASIS). The authors prefer using a roll of tape that can be palpated beneath the drape throughout the case, as needed. We use a mixture of ropivacaine, toradol, and epinephrine for perioperative local analgesia in combination with either a spinal or a general anesthesia. Approach With the knee flexed to 90°, make a paramedial skin incision extending from the medial border of the patella to 3 cm distal to the joint line down to the tibial tubercle, making sure to stay medial to the patellar tendon. Remove some fat pad and inspect the condition of the ACL and the lateral com- partment. We perform a midvastus approach preserving the quadriceps tendon. A mark is made for the entry point of the intramedullary (IM) femur guide about 1 cm anteromedial and superior to the intercondylar notch. With the knee flexed to 45°, make a starting point using a 5-mm awl. Keep knee flexed and drill the entry point. Use rod pusher, to push IM rod into the femur until the rod pusher abuts the femur (Figure 27-1). The IM rod is placed as a guide for flexion of the femoral component. The femoral component would be flexed approximately 10° from the sagittal plane of the femoral shaft. This guide can simultaneously be used as a patellar retractor. Preparation of the Femur The author removes the osteophytes on the medial aspect of the medial femoral condyle and notch with a rongeur before marking the center of the femoral condyle. Then the center of the femoral guide is marked with a marking pen. Alternatively, one can use the technique of Shakespeare by measuring the distance from the lateral edge of the medial femoral condyle as 13, 14, and 15 mm for small, medium, and large components, respectively. This will ensure the meniscal bearing to be seated 2 mm medial from the medial aspect of the wall of the tibial tray (Figure 27-2). Choose the size of the femoral component depending on preoperative templating and assessment of the size of the native femur from medial to lateral. There should be no overhang The curved femoral drill guide that is decoupled from the femoral guide is used to position and drill the femoral component position in place. Because the drill guide will slide medially into the tibial defect, removing some cartilage from the lateral aspect of the medial tibial plateau will help in stabilizing the femoral guide into position (Figure 27-3). Link the femoral drill guide to the IM rod with the hinged elbow of the guide pointing laterally to ensure the appropriate position in flexion and extension planes (Figures 27-4 and 27-5). Ensure that the guide is seated on the bone, and make the drill holes that should coincide with the marked center of the condyle. Drill the anterior smaller 4-mm hole followed by the 6-mm drill hole (Figures 27-6 and 27-7). Placing the Guide of the Posterior Femur Place the saw guide for the posterior femur cut into the drill holes on the femoral condyle and tap it in gently (Figure 27-8). Complete the posterior femur cut using a 12-mm broad oscillat- ing saw blade. Make sure that all ligamentous structures, especially ACL and MCL, are well protected by retractors. The thickness of the femoral bone cut should be comparable to what will be replaced with the femoral component (Figure 27-9). The saw guide is then removed using the slap hammer.
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