Kayla Aikins MS2, Brian Gilmer, MD
DFO is a procedure performed to correct mis-alignment of the femur. The femur is the longest bone in the skeleton and meets the pelvis to form the hip joint. The hip joint is a “ball and socket” joint covered by smooth articular cartilage that allows movement. DFO is performed in children and adults who exhibit these abnormal alignments of the femur.
A surgical procedure for correction of malalignmnent in the frontal plane is termed coronal plane femoral osteotomy. This surgical procedure is performed to correct symptomatic coronal plane misalignment of the knee. The knee is made up of the femur, tibia, patella, and fibula. Misalignment of the knee joint often arises due to osteoarthritis and trauma.
In this x-ray the patient is standing up and the weight moves from the hip to the ankle. In this case, the deformity is valgus or ‘knock-kneed’ and too much pressure is passing through the outside of the knee joint. Incidentally the patient has had ACL surgery on both knees in the past and the metal screws can be seen as white objects on each side of the knee. The patient is starting to develop arthritis in the outside portions of the knee (lateral).
Coronal DFO is indicated for patients experiencing abnormal alignments of the bones that involve the knee joint. The procedure should be considered in active patients less than 65 years old (and typically much younger than this since partial knee replacement may be a better option for older patients) who are affected by osteoarthritis or other conditions that result in misalignment of the knee3. Activity level, lifestyle, and general health should be considered prior to surgery. In addition, a variety of medical conditions can result in deformities that may benefit from coronal DFO:
- Isolated arthritis along the lateral compartment of the knee. Arthritis can result from previous trauma, or from genetic predisposition. Surgery allows these patients to shift their weight from the lateral surface of the knee to the medial surface where normal cartilage is located.
- Chronic medial collateral ligament (MCL) tear in valgus alignment requires surgical correction. Otherwise, there is an increased risk that the MCL tear will progress.
- Valgus malalignment of the knee causes pain and discomfort, while increasing risk of lateral meniscus and chondral (cartilage) injury, as well as eventually arthritis (OA). Mechanical realignment should be considered.
The cause of valgus malalignment is not known, in some cases this is simply genetic, however, to consider realignment there has often been prior trauma or surgery that results in the malalignment being severe enough to consider intervention.
To diagnose valgus malalignment, imaging of the proximal tibia, distal femur, hip, and ankle should be performed to allow for coronal plane analysis (see the xray above). A detailed coronal plane deformity analysis helps to determine whether a varus or valgus deformity exists along the mechanical axis. In addition, the thoughtful surgeon will determine whether the abnormality is attributable to the tibia or femur by calculating the angle between the tibial and femoral mechanical axis and knee joint line rather than just assuming the femur is always to blame. Other factors can also help with diagnosis, including a medial proximal tibial angle and intra articular alignment. If it is determined that the abnormality is not along the coronal plane, CT scans are used for further work-up4. Sometimes the problem is rotational rather than purely in the side to side direction. And sometimes, it is both.
The goal of coronal DFO surgery is to prevent progression of osteoarthritis, gait abnormalities, and degenerative joint disease. Surgical intervention helps to realign the coronal axis of the limb.
There are two procedures which can be used to repair coronal misalignment. The lateral opening wedge DFO involves making a incision over the midline of the lateral femur. The iliotibial band is split and the vastus lateralis is elevated from the intermuscular septum. An oscillating saw is used to remove bone from the femur, and the space created is expanded to realign the bones. Bone wedges are taken from the femoral neck and femoral head and placed into the osteotomy site. The surgeon then uses fluoroscopy to visualize alignment and make adjustments. The bones are secured using metal plates and screws. Specifically, distal locking screws are placed. These are strong enough to hold the correction while the bone heals.
Here is one image taken during surgery showing the gap created on the outside of the femur bone.
This xrays shows one plate and screw combination used for holding the osteotomy. You can see that in these images the triangular wedge is barely visible – the osteotomy has healed and filled with the patient’s own bone.
The medial closing wedge DFO is performed in a similar manner, except it is performed on the medial side of the femur, and the opening is closed by bringing the cut ends of bones together, thus altering bone alignment4.
Rehabilitation begins immediately following the surgery. Patients are placed on a deep vein thrombosis prophylaxis agent to prevent blood clots. The surgical site is dressed with sterile cotton and a bandage. The leg is stabilized in an immobilizer that holds it in full extension, and the patient must refrain from walking for 6 weeks with minimal weight-bearing. During that time, specific exercises are allowed to maintain range of motion. After 3 months, radiographs are taken to determine whether or not the deformity was appropriately corrected5.
Sometimes other procedures are needed at the same time and these may impact the recovery protocol. It is important to have a skilled physical therapist to ensure the optimal result.
Risks and complications
As with any major surgery, possible risks and complications associated with coronal DFO include:
- Neurovascular injury
- Iatrogenic fracture
DFO procedures are challenging, and reported complicated rates range from 5% to 63%5. If screws are placed too close to the joint, patients can suffer from intra-articular fractures. Screw and plate failure can occur as well as malunion. If patients are too active too quickly, they can suffer implant failure and collapse of the osteotomy site. Other complications include but are not limited to a pulmonary embolism, anterior knee pain, and arthrofibrosis.
Dr. Gilmer’s Take
The DFO is a powerful procedure that treats the most common deformity resulting in a valgus ‘knock kneed’ stance.
Most of my patients have had prior meniscus surgery, often meniscectomy where some or all of the meniscus has been removed, or ACL surgery which can lead to injury to the cartilage in the outer part of the knee. In other cases, these patients just have wear and tear from being out of alignment. I have found that many times, the osteotomy is the most important part of preserving these knees and that this is more important than the most intuitive procedures such as replacing the cartilage (OCA, OATS surgeries) or meniscal transplant. After a successful osteotomy patients have no restrictions and can even do higher impact activities.
The two most common issues I see with the DFO are the need to remove the large plate, especially common in smaller patients, and the fact that for geometric reasons, the DFO only corrects the alignment when the knee is near extension. This means it may not be as helpful in protecting the knee cartilage when the knee is flexed more. Correction on the tibia by comparison, corrects the deformity in both flexion and extension. This concept is also important in total knee replacement and partial knee replacement.
In my practice DFO is typically for younger patients where joint replacement (arthroplasty) is not a good option because of the risk of premature wear of the metal and plastic components or patients who want to have higher impact activities which are not recommended with joint replacement.
Brian Gilmer, February 2023
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Kayla Aikins is currently a second year medical student at the University of Nevada, Reno School of Medicine.