20

any postoperative complications with denervation of the VMO or VLO and have therefore found no need for the subvastus approach.35 Distally, the incision moves along the medial border of the patellar tendon, leaving a cuff of tissue, and over the tibial plateau, bisecting the medial or lateral meniscus in half, with the knee flexed to 45. The knee is placed in extension when releasing the tibial tissue. From the capsular incision over the tibial plateau, the medial distal capsule is elevated subperiosteally in a single flap off of the medial aspect of the tibial plateau with a knife or key elevator in a full-thickness fashion to avoid stripping the medial collateral ligament (MCL) completely off of the bone. The distal capsular attachment to the tibial metaphysis should be maintained. Staying on bone, the dissection should be carried medially to the fibers of the deep MCL with a small cobb or key elevator, as stated earlier. The fibers of the deep MCL are elevated off the proximal tibia, taking care to maintain the distal attachment. This procedure facilitates a Z retractor placed deep to the MCL to protect the superficial MCL and all vital structures during the operation. When exposing the lateral side of the knee with a lateral midvastus incision, it is important to note this tissue is thin, unlike the medial side of the knee. The incision as described earlier is through the VLO, moving distally through the midsection bisecting the lateral meniscus and continuing to Gerdy’s tubercle. We have found that it is important to release the IT band off of Gerdy’s tubercle to help balance the knee when placing a lateral UKA. The same precautions for the neurovascular structures are carried out whether on the lateral or medial side of the knee. Unlike the medial side of the knee, where flexion and external rotation help the surgeon for visualization, the figure-of-four position is helpful for the surgeon when needing extra visualization for a lateral UKA. FAT PAD AND OSTEOPHYTE EXCISION When beginning the operation, the synovial fluid should be examined to ensure that it is yellow and clear, with no signs of infection. The knee should be thoroughly inspected using a systematic approach. Hoffa’s fat pad is a potential source of 92 Dunn et al postoperative anterior knee pain, and therefore, a generous fat pad excision is recommended in the figure-of-four position for a medial UKA to decrease the risk of fat pad impingement postoperatively.36,37 Successful excision of Hoffa’s fat pad allows for improved visualization of the patellofemoral and lateral joints. Care should always be taken not to violate the patellar tendon. Osteophyte removal from the patella is routinely performed during patellar resurfacing, similar to TKA.38 Osteophytes are circumferentially (360) removed with a small hand rongeur. A small rongeur and nasal rasp are then used to ensure a smooth edge. No osteophytes are removed from the femur or the tibia unless full extension is blocked or a cutting jig does not sit flush on the patient’s anatomy. Removal of osteophytes from the intercondylar notch is critical to avoid ACL impingement; however, this step is not completed until the end of the procedure, along with any overhanging osteophytes on the tibia or femur, to avoid a stress riser to either bone.39 BONE CUTS Bone cuts are initiated with the distal femoral cut first, followed by the proximal tibial cut, and then, the femoral posterior and chamfer cuts, with a gap-balancing technique, similar to TKA.40 The advantages of this approach include (1) better access to the deepest portion of the tibial plateau, which is often more posterior than the tibial stylus can reach with the distal femur intact, (2) easier removal of the tibial cut bone fragment,41 and (3) the creation of a pilot hole, in which a self-retaining patellar retractor may be placed to improve visualization. Distal Femoral Cut Using an IM Guide When making the distal femoral cut with the IM guide, the knee is flexed to approximately 30 and held at the ankle (Fig. 6). The patella is laterally translated to expose the intercondylar notch, trochlear groove, and femoral insertion of the posterior cruciate ligament (PCL). A pilot hole is drilled approximately 1 cm superior to the femoral insertion of the PCL, 1 cm medial or lateral to the apex of the intercondylar notch, and in line with the central axis of the femoral shaft.42 If overgrowth has occurred, a rongeur is used for a better starting position. We always err with a starting hole on the side that has the disease. To avoid slipping off from the appropriate starting position, the catheter tip of the pilot drill is axially loaded through the articular cartilage until it is engaged in the subchondral bone before the drill is started. Suction is then placed Fig. 6. Distal femur jig held in place with Z retractor. UKA: Intramedullary Technique 93 into the drill hole to decrease IM pressures before inserting the IM guide rod.43 The long IM rod guide with appropriate distal femoral cutting block is then inserted slowly. A short IM guide is available when a long-stem hip prosthesis is used, which is one of the reasons that we obtain 3 standing films preoperatively. A short guide is rarely used unless a bowing deformity of the femur necessitates its use. The angulation of the cutting block should be adjusted according to preoperative templating, approximately 6 for a varus knee and 3 or 4 for a valgus knee. The cutting block

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25