Femoral Varus Osteotomy

Introduction

The valgus knee (see Fig. 11.1 ) is usually associated with hypoplasia of the lateral femoral condyle and a superior lateral directed joint line. The ankle joint is frequently obliquely orientated to the floor parallel to the knee joint in this situation. Corrective osteotomy performed at the level of the femoral deformity to restore the joint line parallel to the floor will also make the ankle 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 osteotomies. Each has its own advantages and disadvantages. The clinical outcomes following femoral osteotomies parallel those of tibial osteotomies; however, they are much less common as is the literature on them. Valgus knees are less frequent than varus knees and the disease pattern frequently involves the patellofemoral joint when the knee is in valgus. Correction of both lateral and patellofemoral arthritic conditions is technically more demanding and less predictable.

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 (ACL) or posterior cruciate ligament (PCL) 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 utilize is dependent upon 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 the 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 find that for greater corrections there is a tendency for the distal fragment to flex because it remains hinged on the medial side at the level of the adductor tubercle, which is in a relatively posterior axis. The medial hinge on the femur, however, is not supported by an additional structure such as the fibula when performing high tibial valgus osteotomy (HTO) and is more prone to fracturing and displacing. In addition, the iliotibial band starts to become very tight when corrections greater than 15 degrees are attempted. A shortened leg length on the affected side is another relative indication to use an opening wedge varus-producing osteotomy, which tends to equalize leg lengths.

The supracondylar reverse dome osteotomy remains a very powerful osteotomy for large angular corrections and is my choice for corrections greater than 15 degrees. It traditionally required the use of an angled blade plate to obtain stable fixation; however, locking plates or retrograde intramedullary nails have made fixation much easier.

Closing wedge varus-producing femoral osteotomies heal more rapidly than the other two and provide a source of autogenous bone graft in the event there is an osteochondral defect of the lateral femoral condyle that requires osseous bone grafting. If the affected leg is longer, a closing wedge osteotomy is preferred to equalize leg lengths. Fixation has always been described using a 90-degree angled blade plate ; however, medial locking buttress plates now make the procedure technically much easier to perform with more precise corrections.

Planning

The goal of femoral osteotomy correction is similar to that of tibial valgus-producing osteotomy. If weight-bearing x-ray images demonstrate intact joint spaces and valgus malalignment is present with mechanical axis forces through the lateral compartment, correction of the mechanical axis is to the midline if an articular cartilage defect is being unloaded (see Fig. 11.2 ). This normalizes forces across the joint. If there is joint space narrowing or a large articular cartilage defect that is undergoing repair, the aim is to unload the lateral compartment by only 2 degrees, which corresponds to the top of the medial tibial spine. In this way, a premature wear of the medial compartment is less likely.

Long alignment x-ray images in a double stance AP phase are required for calculating angular correction (see Figs. 11.3 and 11.4 ). 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 then 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 the placement of a chisel to be planned for the use of an angled blade plate relative to the tibial femoral joint line ( Fig. 11.4 ).