Measure the amount of varus-flexion deformity on anteroposterior and lateral knee radiographs. Confirm the radiographic degree of the deformity with physical examination.

Note any elongation on the lateral side (Fig. 1, yellow arrowhead) and measure the amount of the deformity that is correctable with valgus stress on physical examination.

Without using a tourniquet, expose the knee in flexion with a medial parapatellar approach and a medial periosteal elevation proximal to the pes anserine insertion. (The use of a tourniquet during exposure is possible with this technique; however, we do not use one during exposure as knee flexion substantially reduces bleeding.) Release both cruciate ligaments (this technique is designed for a posterior stabilized knee system) and evert the patella.

Subluxate the tibia anterior to the femur using the Ran-sall maneuver⁶ by hyperflexion and external rotation of the tibia to expose the entire articular surface of the tibia.

Cut the proximal part of the tibia at 90° to the long axis of the tibia so that the cut surface is parallel to the tibial plafond. Appropriate slope for a posterior stabilized system should be incorporated into the cut.

Cut 8 to 10 mm of bone off of the uninvolved lateral tibial plateau. Cut a lesser amount if there is any elongation on the lateral side based on the anteroposterior radiograph. Remove all osteophytes and perform a reduction osteotomy to decompress the medial soft-tissue sleeve. Confirm tibial alignment (Fig. 3).

Remove 8 to 10 mm of the distal part of the femur with a valgus cut of 5° to 7° based on the mechanical axis of the femur.

Inflate the tourniquet. Bring the knee to full extension. Place a 20-mm spacer block into the extension gap and check stability. The gap should be asymmetric and trapezoidal. If the spacer block can be placed in the lateral side, the bone cuts are adequate (Fig. 4). If the spacer block cannot fit into the lateral side, then additional bone resection is required. There should be a “springy give” of 2 to 3 mm in the lateral side when a varus force is applied. The medial side will be tight and requires release.

Remove the spacer and place a lamina spreader to tension the extension gap. Irrigate and dry the posterior aspect of the capsule. Remove any remnants of the posterior cruciate ligament (PCL) and menisci. Release the tight posteromedial aspect of the capsule with electrocautery at the level of the tibial cut from the insertion of the PCL to the posterior margin of the sMCL (Fig. 5). Use a periosteal elevator to evaluate the completeness of the release (Fig. 6).

Check the extension gap again with varus/valgus stress tests using a spacer block. If the extension gap is still trapezoidal and tight medially, proceed with pie-crusting of the sMCL.

With a lamina spreader in the extension gap, palpate the tight fibers of the sMCL at the joint level. To pie-crust the sMCL, use a number-11 scalpel blade and stab the tight bands in an oblique manner three, four, or five times (Fig. 7). Place the spacer block back and manipulate the knee with a repeated valgus stress. Repeat pie-crusting and serial manipulations until a rectangular extension gap is achieved.

A balanced extension gap allows for 2 to 3 mm of “springy give” with the spacer block in place on both the medial and the lateral side when you apply a valgus and varus force, respectively (Fig. 8).

Balance the flexion gap using the “parallel to the tibial cut technique.”^7,8

Bring the knee to 90° of flexion. Size the femur appropriately using either an anterior or posterior referencing system to restore the posterior offset and avoid so-called notching of the anterior cortex. Place the femoral cutting block and use a lamina spreader in the middle of the block (Fig. 9).

While an assistant is manually unloading the medial side of the knee, measure the medial and lateral sides of the flexion gap. The size of the flexion gap should be equivalent to, or 2 mm less than, the size of the extension gap.

Rotate the cutting block until the medial and lateral flexion gaps are equal and symmetric (Fig. 10). Use a spacer block to assess flexion stability. Make the chamber and box cuts. Lateralize the femoral component to match the lateral edge to the lateral condyle to reduce the Q angle. Place the trial components and test the stability of the knee through a full range of motion.

The inside-out technique is indicated during total knee arthroplasty for any fixed varus-flexion deformity of the knee of >10°.

Correctable varus-flexion deformities of the knee do not require this technique.

Cut less bone when there is elongation of the lateral structures as evidenced by the preoperative standing anteroposterior radiograph or else the extension gap may become too large.

Perform the posteromedial capsular release using electrocautery at the level of the tibial cut from the insertion of the PCL to the posterior border of the sMCL. Be aware of the neurovascular structures in the posterior aspect of the knee when performing this release.

Pie-crust the tight bands of the sMCL with three, four, or five oblique stabs using a number-11 scalpel blade. Be careful to avoid transecting the sMCL completely during the controlled lengthening process.

Serial manipulations, complete capsular release, and repeat pie-crusting may be required before a balanced extension gap is achieved.

Balance the flexion gap using the “parallel to the tibial cut technique.” Restore femoral posterior offset, avoid notching, and lateralize the femoral component.

How do you avoid overreleasing the sMCL?

What are the advantages of balancing the extension gap prior to the flexion gap?

What steps should you take to ensure an accurate tibial cut 90° to the mechanical axis?

How do you avoid cutting more than enough tibia when the lateral structures are elongated?

What are the advantages of using the “parallel to the tibial cut technique” compared with using the Whiteside line or the transepicondylar axis for femoral rotation?