History

Medial opening wedge HTO has increased in popularity in recent years for a number of reasons. The theoretical advantages of employing an opening wedge osteotomy over a closing wedge procedure include the following:

The disadvantages of the medial-sided procedure include the following:

Less common surgical options available to modify the coronal and sagittal alignment of the proximal tibia include the dome osteotomy or gradual correction with an external fixator. These operations both offer the ability to correct large deformities that are not correctable by either opening or closing wedge techniques. These techniques are beyond the scope of this chapter.

Imaging

Radiographic assessment of an HTO candidate varies slightly depending on the indication for surgery. However, regardless of the indication, all patients at our institution undergo a routine knee series including a full-length alignment film. The knee radiographs include bilateral anteroposterior (AP) weight-bearing films in full extension, bilateral posteroanterior weight-bearing films taken at 45 degrees of knee flexion, and lateral and skyline views of the affected knee. In the patient with medial compartment osteoarthritis, the radiographs are needed to assess the extent of the medial compartment osteoarthritis and to rule out extensive degeneration in the patellofemoral and lateral joint compartments. Other findings to note on the preoperative radiographs are the distal femoral and proximal tibial angles for deformity, sagittal tibial slope, lateral tibial subluxation, and joint incongruence. On the full-length radiograph, the weight-bearing axis is drawn from the center of the hip to the center of the ankle, which determines where the load passes through the knee joint.

A number of potential methods can be used to calculate the size of the osteotomy.1–3 We currently employ the method described by Dugdale and colleagues,² which corrects the weight-bearing axis to 62.5% of the width of the plateau, or 3 to 5 degrees of mechanical valgus. An example of the calculation can be seen in Figure 70-1. If there is excess varus malalignment because of soft tissue laxity, the difference in congruence angle on the affected and unaffected legs noted on the bilateral standing full-length AP radiograph is subtracted from the correction.

Indications and Contraindications

Indications for an HTO include clinical and radiographic varus and (1) medial compartment arthrosis with or without mild to moderate asymptomatic radiographic patellofemoral arthrosis; (2) symptomatic ligamentous instability with medial compartment arthrosis; (3) recurrent ACL rupture with significant joint deformity; and (4) medial compartment pain in the setting of previous total medial meniscectomy, osteochondritis dissecans, or significant chondral damage.⁴

Isolated medial-sided degenerative joint disease with varus malalignment remains the most common indication for opening wedge HTO. The patient should be motivated and aware that pain relief may not be complete or permanent. Patients under the age of 50 and with a body mass index (BMI) of less than 25 are good candidates and demonstrate improved survivorship.5,6 An HTO in a patient with an unstable knee and malalignment may improve pain and instability symptoms and potentially delay the onset of cartilage degeneration.^7,8

Absolute contraindications to HTO for medial compartment osteoarthritis include inflammatory arthritis and significant lateral tibiofemoral joint disease. Poorer outcomes after HTO have been correlated with severe articular destruction,⁹ significant patellofemoral disease,¹⁰ increased age,^6,9,11 lateral tibial thrust,⁶ decreased range of motion,⁶ or joint instability.¹² Recent literature presents evidence that ACL deficiency correlates with higher likelihood of long-term survival, suggesting that joint instability may not predict a poorer outcome.⁵ The preceding findings should be considered with each patient’s clinical picture, serve as a basis to counsel each patient on the potential for a good functional outcome, and should not be thought of as definitive reasons to avoid performing an osteotomy.