A midline incision is made from the superior pole of the patella to the tibial tubercle. The incision can range from 10 to 16 cm depending on patient size, the presence of any previous incisions, and surgeon experience. Again, the length of the incision is not critical to the patient’s recovery and should be optimized to facilitate a safe and accurate surgical procedure (Figure 2). Subcutaneous mobilization is required both medially and superiorly to allow patellar mobility. A horizontal arthrotomy is made along the inferior aspect of the vastus medialis obliquus (VMO), leaving a cuff of retinaculum on the VMO for closure (Figure 3, A). The arthrotomy is completed in a standard manner along the medial patellar tendon. The reflected retinaculum, which contains the medial patellofemoral ligament, is tagged for identification, protection, and retraction (Figure 3, B). To facilitate exposure, I create a subcutaneous mobile window, through which different parts of the knee joint can be visualized depending on the position of the knee, but the entire joint is not visualized at any one time. For example, with the knee placed in the figure-of-4 position, the posterolateral aspect of the knee is well visualized.

The extensor mechanism is mobilized to allow patellar subluxation. The patella and VMO are tethered medially and released through a series of three steps. First, unlike a true subvastus exposure, in which the VMO is released from the intermuscular septum up to the Hunter canal to allow patellar eversion, the mini-subvastus arthrotomy incises just through the retinacular cuff of the VMO on its medial border (Figure 4, A and B). This allows significant lateral mobility of the VMO. In large, muscular patients, the VMO often will “self-release” a few centimeters above the joint line along the intermuscular septum. Next, the synovial capsular reflection underneath the VMO is released (Figure 4, C and D). Depending on the amount and thickness of the synovium, a limited synovectomy can be done at this time. Finally, the patellar tendon fat pad is excised (Figure 4, E and F). These three steps allow the patella to be subluxated laterally.

A Z retractor is placed under the VMO laterally, and the knee is flexed to 90°. It should be emphasized that the knee is flexed to only 90°, leaving it in an in situ position; much of the operation is performed with the knee at this angle. This avoids the hyperflexed knee position routinely described in traditional TKA techniques, in which the tibia is dislocated forward, damaging the posterior knee capsule.

A 9-mm drill is used to open the intramedullary canals of the distal femur and the proximal tibia. An intramedullary distal femoral alignment guide is positioned on the anteromedial surface of the femur. Two parallel threaded pins are drilled into the femur. The distal resection is checked with an angel wing, and the final position of the guide is adjusted to ensure adequate distal femur resection. A third pin is then drilled in a different plane to provide secure fixation of the cutting guide. This distal femoral cutting guide arcs around the femur from anterior to medial, allowing an initial cut of the medial femoral condyle from anterior to posterior. Then the saw can be angled from more medial to lateral to complete the distal femoral cut.

Tibial preparation is next. An intramedullary cutting guide is used to make the tibial cut. Although both intramedullary and extramedullary guides are available, the intramedullary tibial guide requires fewer soft-tissue landmarks for orientation and is thought to provide a more accurate tibial resection. Once the tibial cut is made, the knee is brought into full extension. The cut tibia is grasped on its anteromedial surface and rotated out, medial side first (Figure 5). As the tibia rotates out, the medial meniscus, posterior cruciate ligament, and lateral meniscal attachments are released sharply off the cut tibia with a knife. With the knee still in full extension, the meniscal remnants are removed from the posterior capsule with electrocautery, and the extension gap is checked to ensure that adequate bone has been resected for final implants.

The knee is brought back into a 90° flexed position. The distal femur is measured with a posterior reference guide, femoral rotation is determined, and the low-profile distal femoral four-in-one cutting block is positioned on the distal femur. Saw cuts are made, and bone fragments are removed. If a posterior stabilized implant is being used, the femoral notch cut is made at this time. The patella is allowed to subluxate back into an anatomic position, and the knee is flexed again to 90°. With posterior pressure placed on the proximal tibia, the posteromedial osteophytes are visible through the mobile window and can be removed with a curved osteotome (Figure 6). Then the patella is subluxated laterally again with a Z retractor; the knee is brought into a figure-of-4 position, bringing the posterolateral aspect of the knee into view through the mobile window; and the posterolateral osteophytes are removed with a curved osteotome.