Total Knee Arthroplasty in Severe Varus Deformity

Severe varus deformity appears to have no predilection for male or female patients. Typically, patients report some varus alignment in their knees since childhood and may have a history of medial meniscectomy. The deformity gradually progresses, and the patient may present with significant disability any time after the age of 50 years. Lateral subluxation of the tibia on the femur is not uncommon. The source of the varus deformity is the tibial side of the joint, in contrast to the valgus knee, for which the femoral side of the joint is responsible ( Fig. 3.1 ).

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Varus deformity is usually caused by a deficiency of the medial tibial plateau, and often lateral subluxation of the tibia is present.

The knee is exposed through the standard median parapatellar arthrotomy. Routine exposure proceeds with excision of the anterior horn of the medial meniscus. This provides access to the plane between the proximal tibial plateau and the deep medial collateral ligament (MCL). Into this plane a 1-cm curved osteotome is passed posteriorly to the level of the semimembranosus bursa. This accomplishes an initial release of the deep MCL. If present, the anterior cruciate ligament is resected. The tibia is then manipulated into flexion and external rotation and delivered in front of the femur ( Fig. 3.2 ). Peripheral femoral and tibial osteophytes are removed to further release the medial structures that were tented over them ( Fig. 3.3 ).

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Tibia is delivered in front of the femur for the initial tibial resection.

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Initial correction is obtained by removing peripheral osteophytes (arrows) from the femur and tibia that tent up the medial collateral ligament.

Unlike in the valgus knee, ligament balance in flexion and extension are interrelated. The valgus knee can be balanced in flexion before any releases by proper rotational alignment of the femoral component (see Chapter 4 ). In the varus knee, however, the knee should be balanced in extension before it is balanced in flexion (via proper femoral component rotation).

Medial Release in Extension

As noted earlier, routine exposure of the knee and removal of femoral and tibial osteophytes accomplishes an initial medial release. For many varus knees, this is sufficient to achieve mediolateral balancing in extension. For severe varus knees, however, an additional release is necessary. I believe this is most successfully and safely achieved by the shift and resect technique.

Shift and Resect Technique

After the tibia has been delivered in front of the femur, an initial conservative tibial resection is performed. The level of resection is based on the intact lateral side. The amount of lateral resection is approximately 10 mm, including any residual cartilage for the use of a 10-mm composite tibial thickness ( Fig. 3.4 ).

The angle of the resection is perpendicular to the long axis of the tibia and has a 3- to 5-degree posterior slope (see Chapter 2 for exceptions to this amount of posterior slope). The tibia is next measured for the size of tray. One size smaller is then chosen and shifted laterally to the edge of the cut surface of the lateral plateau. Preliminary tibial rotation of the tray is based on alignment with the medial third of the tibial tubercle. A marking pen is used to outline the uncapped portion of the medial tibial plateau ( Fig. 3.5 ). This bone is removed with an angle of resection that is perpendicular to the tibial resection ( Fig. 3.6 ). The MCL has been freed of its attachment to this resected bone before its removal, and the ligament should be carefully protected during the resection. The resection can be accomplished with a rongeur, a saw, or an osteotome. It is sometimes helpful to define the resection with multiple small drill holes that perforate the sclerotic medial bone. In mild-to-moderate varus knees, I resect a 3-mm rim of proximal tibia, including osteophytes, even before performing the tibial resection ( Fig. 3.7 ).

Formal Medial Collateral Ligament Release From the Tibia

It is extremely rare for me to perform a formal distal MCL release. Should this be necessary, I would proceed with one of the following techniques. The first is a pie-crusting release. Releasing anterior fibers affects the flexion space, whereas releasing posterior fibers affects extension balancing. To remember this, I use the mnemonic “atrial fibrillation/pulmonary embolus” or AF/PE (anterior-flexion/posterior-extension). The pie-crusting can be done in a stepwise fashion from inside-out or outside-in using a laminar spreader to tension the ligament.

Alternatively, I would perform a classic subperiosteal MCL release as described by Insall, progressing distally in stages until adequate release was obtained. I avoid this type of release, if possible, because it carries the danger of catastrophic loss of medial support at the time of the surgical release or in the early postoperative course secondary to minor trauma.