Several studies have investigated the association between valgus limb alignment and the development and progression of lateral compartment osteoarthritis (OA). Brouwer and colleagues ¹ found that valgus alignment was associated with a borderline significant increase in the development of knee OA (odds ratio [OR] 1.54; 95% confidence interval [95% CI] 0.97–2.44). Other studies have found a strong correlation between valgus alignment and the progression of knee OA.^2,3 A cross-sectional study by Issa and colleagues⁴ showed that the presence of cartilage defects in the lateral compartment increased with greater valgus malalignment. Lateral unicompartmental knee arthroplasty (UKA) is performed much less commonly than medial UKA, and therefore the available data on long-term outcomes are limited.

In addition, modern knee procedures such as osteochondral resurfacing and meniscal transplantation have evolved in recent years and gained popularity, often necessitating a concomitant joint unloading procedure to increase the longevity of the reconstruction. Corrective varus-producing osteotomies around the knee to correct valgus alignment are common and a valuable adjunct to other knee surgeries to improve outcomes.

Preoperative Considerations

History

In general, proximal tibial osteotomy is used to correct varus limb malalignment, and distal femoral osteotomy is used to correct valgus limb malalignment. A proximal tibial osteotomy can be used to correct valgus malalignment, but this usually leads to a change in the joint line orientation (Fig. 71-1).⁵ Perhaps, small corrections can be tolerated in the proximal tibia.

Figure 71-1 A valgus-producing high tibial osteotomy results in obliquity of the tibiofemoral joint line.

The main differences between proximal tibial and distal femoral osteotomies are their effect on the tibial slope and the patellar height.

It is well known that proximal tibial osteotomy alters the tibial slope, with opening wedge having the tendency to increase the slope ⁶ and closing wedge having the tendency to decrease the slope. This change in the slope has an effect on knee kinematics and stability. In addition, the tibial osteotomy will alter the contact mechanics through a full range of motion, whereas the femoral osteotomy will change the contact forces mainly near extension.⁵

Although there are complications that may accompany any osteotomy including femoral osteotomy, the alignment changes with distal femoral osteotomy involve only the coronal plane. In the varus knee, slight overcorrection into valgus is encouraged, but in the valgus knee the most common complication is overcorrection into varus, and this must be avoided. Patellar height changes after distal femoral osteotomy are also minimal and largely ignored ⁷ compared with proximal tibial osteotomy.

Physical Examination

Patient evaluation begins by taking a good history and performing an appropriate physical examination to determine if the patient is an appropriate candidate for realignment surgery.

Imaging

Radiographic evaluation should include weight-bearing anteroposterior (AP) and 45-degree flexion posteroanterior (PA; Rosenberg) views, lateral, and skyline or merchant views of both knees for comparison. If assessment of limb alignment is considered, bilateral long-leg views (hips to ankles) should be performed. Magnetic resonance imaging (MRI) may be indicated depending on the differential diagnosis—that is, meniscal or cartilage status.

Sometimes a single standing long-leg view reveals an obscure deformity if clinical findings do not correlate with the initial long-leg view (Figs. 71-2), especially if there is a valgus thrust.

Figure 71-2 A 16-year-old boy who was indicated for lateral meniscal transplantation. Long-leg view initially did not reveal a big valgus deformity, although clinically he was in valgus; a standing one-leg view was ordered and showed the increase in the valgus deformity.

The mechanical axis, which is a line drawn from the center of the femoral head to the center of the talus (Fig. 71-3), should normally pass through the center of the knee joint between the two tibial spines or just lateral to the medial spine.

Figure 71-3 The mechanical axis is a line drawn from the center of the femoral head to the center of the talus on a standing long-leg view.

When a distal femoral osteotomy is indicated, the degree of correction is calculated by use of the long-leg view to make the mechanical axis pass through the medial tibial spine and not beyond that point to prevent overcorrection and medial compartment overload.

A line is drawn from the center of the femoral head to the medial tibial spine. Another line is drawn from the center of the talus to the same point (medial tibial spine), and the angle between these two lines is the angle of correction (Fig. 71-4).

Figure 71-4 The angle of correction between a line, K, drawn from the center of the femoral head to the desired level on the tibial articular surface (usually between the two tibial spines) and another line, M, drawn from the center of the talus to the same point on the tibial articular surface.

Rather than calculating the correction angle in degrees, calculating the actual correction in millimeters is more practical and avoids an extra step. This conversion is made by drawing the planned osteotomy wedge or triangle (planned level, length, angle of inclination, and angle of correction) on the distal femur and measuring the width of the base of this wedge at the lateral femoral cortex (Figs. 71-5 to 71-7).

Figure 71-5 The first method of converting the angle of correction into millimeters. A wedge representing the planned osteotomy with the planned level, length, angle of inclination, and angle of correction is drawn, and the width of the base of this wedge at the lateral femoral cortex is the millimeters of correction (here 10.2 mm).

Figure 71-6 The second method of converting the angle of correction into millimeters. A line representing the osteotomy cut with the planned level and angle of inclination is drawn. The length of this line is measured (here 70.2 mm). Another line with the same measured length is drawn over one of the limbs of the angle of correction starting from the tip (the desired point of correction on the tibial articular surface). The width of the base of the triangle formed is the millimeters of correction.

Figure 71-7 Follow-up long-leg radiograph of the patient shown in Figs. 71-3 to 71-6 3 months after the distal femoral lateral opening wedge osteotomy with a 10-mm plate showing the mechanical axis passing between the two tibial spines as planned before surgery.