Introduction

The valgus knee (Figure 9–1) is usually secondary to hypoplasia of the lateral femoral condyle resulting in a superior lateral directed joint line. Corrective osteotomy is most appropriately performed at the level of the deformity to restore a joint line that will be parallel to the floor. For this reason, correction of valgus malalignment is performed through the femur. As in tibial corrective osteotomies, osteotomies may be closing wedge, opening wedge, or reverse dome. Each has advantages and disadvantages. The clinical outcomes following femoral osteotomies parallel those of tibial osteotomies; however, femoral osteotomies are much less common, as is the literature on them.^1,² One possible reason is that the disease pattern frequently involves the patellofemoral joint when the knee is in valgus, and correction of both arthritic conditions is technically more demanding and less predictable.

Figure 9–1 Valgus mechanical alignment is associated with hypoplasia of the lateral femoral condyle and a superior lateral directed joint line.

Indications

Femoral varus-producing osteotomy is indicated for unloading a laterally based articular cartilage defect, pain secondary to lateral compartment overload, or lateral compartment osteoarthritis with intact medial and patellofemoral articulations. Unlike tibial osteotomy, which is very effective for addressing instability such as anterior cruciate ligament or posterior cruciate ligament secondary to sagittal slope correction, changing the flexion or extension of the distal femur has no influence on instability. Overall, femoral osteotomies are technically more challenging to perform because of the larger soft tissue envelope, the longer lever arm, which can displace the osteotomy as it is being performed, and its proximity to the articular surface of the trochlea and the femoral artery. My choice of which type of femoral osteotomy to use is dependent on the degree of correction, the leg length discrepancy, and the need for bone grafting of an osteochondral defect. Like opening wedge tibial osteotomies, an opening wedge femoral osteotomy is technically easier to perform than closing wedge or reverse dome osteotomies because it allows a “dial-in” accurate correction. It has the disadvantage of requiring the use of bone graft; however, I have found that allograft materials (specifically a combination of cancellous allograft bone chips with demineralized bone matrix) heal in the same amount of time as autograft bone.

I use opening wedge femoral osteotomies for corrections up to 15 degrees because I have found that for greater corrections, the distal fragment has a tendency to flex as it remains hinged on the medial side at the level of the adductor tubercle, which is in a relatively posterior axis. In addition, the iliotibial band starts to become very tight as corrections greater than 15 degrees are attempted. A shortened leg length on the affected side is another relative indication for use of an opening wedge varus-producing osteotomy, which tends to equalize leg lengths.

The supracondylar reverse dome osteotomy remains a powerful osteotomy for large angular corrections and is my choice for corrections greater than 15 degrees.³ It requires the use of an angled blade plate to obtain stable fixation or use of another fixed-angle device.

Closing wedge varus-producing femoral osteotomies heal more rapidly than the other two types of osteotomies and provide a source of autogenous bone graft if an osteochondral defect of the lateral femoral condyle requires osseous bone grafting. If the affected leg is long, a closing wedge osteotomy is preferred to equalize leg lengths.

Planning

The goal of femoral osteotomy correction is similar to that of tibial valgus-producing osteotomy. If weight-bearing x-ray films demonstrate intact joint spaces and valgus malalignment is present with mechanical axis forces through the lateral compartment, then correction of the mechanical axis is made to the midline if an articular cartilage defect is being unloaded (Figure 9–2). This normalizes the forces across the joint. If joint space narrowing is present or a large articular cartilage defect is undergoing repair, then the aim is to unload the lateral compartment by only 2 degrees, which corresponds to the medial tibial spine. In this way, premature wear of the medial compartment is less likely.

Figure 9–2 The desired mechanical axis correction is to the midline of the knee (red line) in a situation of cartilage repair with no joint space narrowing of the lateral compartment or a 2-degree overcorrection to the medial tibial spine (blue line) when osteoarthritis or joint space narrowing is present.

Long alignment x-ray films in a double-stance anteroposterior phase are required for calculating angular correction (Figures 9–3 and 9–4). A line from the center of the femoral head is projected to the desired mechanical axis of either the center of the knee or the medial tibial spine to the proposed position of the foot. An angular correction then goes from the existing center of the ankle to the proposed mechanical axis point at the knee and then to the new ankle position. This acute angle is the angular correction. This angular correction is converted to opening or closing millimeters using digital x-ray templates to plan for an opening wedge osteotomy on the lateral side of the distal femur or a closing wedge osteotomy on the medial side of the femur above the adductor tubercle and trochlea. This angle also allows planning for placement of a chisel for use of an angled blade plate relative to the tibial femoral joint line (see Figure 9–4).

Figure 9–3 The angle of correction for a varus-producing femoral osteotomy is measured on a long alignment x-ray film. The angle from the existing center of the ankle to the proposed mechanical axis at the knee (see Figure 9–2) and back to the new position of the ankle represents the angular correction. This angle is applied to the level of the opening or closing wedge osteotomy on the distal femoral metaphyseal–diaphyseal junction. The measurements in millimeters, x, is the correct opening or closing osteotomy. Opening wedge systems generally have spacer plates in millimeters that correspond to the preoperative planning. Closing wedge systems usually have angular increments on the osteotomy jigs that accurately measure in degrees the angular correction. Digitized x-ray systems with built-in software, calibrated for magnification error, make the planning very straightforward (General Electric web-based Centricity software [GE Healthcare, Waukesha, WI]).

Figure 9–4 The angular correction is calculated and identical to obtained in Figure 9–3. A 95-degree blade plate is used for fixation of a supracondylar reverse dome varus femoral osteotomy, although other fixed-angle devices, such as a locking plate, may be used. The corrective angle α is measured from the lateral cortex of the femur to the intersection of the proposed position of the 95-degree angled blade plate. Generally, angled metallic triangles that have the angle α are placed along the plate portion of the angled blade plate. This allows placement of a guidewire along the plane of the entry blade. The seating chisel then passes along the guidewire prior to the supracondylar femoral dome osteotomy. Once the osteotomy is completed, the 95-degree blade plate is placed along the tract of the seating chisel, and the alignment of the leg is corrected with a varus force until the plate portion fits flush to the lateral femoral cortex. An articulated compression device is applied, the osteotomy site is compressed, and screw fixation completes the stabilization of the osteotomy.

Opening wedge varus femoral osteotomy

Technique and Aftercare

An opening wedge femoral varus-producing osteotomy is performed through a midline incision. Figure 9–5 shows an appropriate case example, and Figure 9–6 outlines the surgery in stepwise fashion. The deep exposure can be performed through a lateral subvastus approach to approach the lateral distal femur for an extraarticular surgery. The lateral subvastus approach can be combined with a tibial tubercle osteotomy to expose the entire distal femur and joint without a muscle split. I usually use a lateral parapatellar arthrotomy to expose the distal lateral femur as well as the patellofemoral articulation.