What is proximal femoral focal deficiency?

Proximal femoral focal deficiency is a complex birth defect in which the upper part of the femur bone (in the thigh) is either malformed or missing, causing one leg to be shorter than the other. This difference causes functional problems with a child’s ability to walk and can stress other bones and joints in the body in an effort to compensate.

Proximal femoral focal deficiency (PFFD) is an uncommon condition that affects about 1 in every 200,000 children, and can vary in severity from child to child. Often children with PFFD have other bone and muscle disorders — such as malrotation, limb-length discrepancies, fibular hemimelia, joint instability and muscle weakness — that also must be addressed.

There are several treatment strategies and alternatives for children with PFFD, however there is not a “one size fits all” solution. For this reason, an experienced multidisciplinary team is needed to develop a customized treatment plan to address the child’s specific needs. Pediatric orthopedic surgeons, nurses, prosthetic experts and physical therapists must collaborate to determine whether surgery, leg-lengthening procedures, prosthetics — or a combination of these treatments — will offer the child the best chance to increase functionality.

Causes of PFFD

The causes of proximal femoral focal deficiency remain largely unknown and the disorder does not appear to be genetically linked. In most cases, researchers suspect PFFD is caused by a disruption during early prenatal development, which can be caused randomly or as a result of an outside force such as an infection or trauma.

Researchers have proven that the drug thalidomide, when taken by the pregnant mother, can cause PFFD and other limb deficiencies to unborn children. Pregnant mothers taking this medication for another condition should talk to their doctor immediately about the risk of PFFD and other possible birth defects linked to this medication.

Symptoms of proximal femoral focal deficiency

While the symptoms of proximal femoral focal deficiency can vary from child to child, classic presentation includes a femur (thigh) that is:

• Shortened
• Externally rotated (turned outward)
• Flexed
• Abducted (leg pivots from the hip at an abnormal angle)

Other symptoms of PFFD may include:

• Unstable or absent hip joint on the affected leg
• Unstable knee joint on the affected leg

In addition, proximal femoral focal deficiency has been linked to other anomalies such as:

• Shortened or absent fibula in the lower leg (fibular deficiency)
• Flat feet (valgus foot)
• Club foot
• Spine differences
• Cleft palate
• Congenital heart defects

For 85 percent of children with PFFD, the disorder will only affect one leg. The others will have bilateral PFFD affecting both legs.

Testing and diagnosis

Children with proximal femoral focal deficiency are diagnosed at birth when the clinical presentation is obvious, or before birth using prenatal imaging. No matter when the disorder is first identified, the clinical appearance is similar: a shortened femur that is externally rotated, flexed and abducted.

At Children’s Hospital of Philadelphia (CHOP), a trained pediatric orthopedic physician will perform a physical and visual examination of your child, and get a complete medical history. The goal of evaluation is to better understand your child’s anatomy, the severity of their condition, and their functional abilities.

In many cases, doctors will order imaging tests such as:

• X-rays, which produce images of bones.
• EOS imaging, which creates 3-dimensional models from two flat images. EOS images are taken while the child is in an upright or standing position, enabling improved diagnosis due to weight-bearing positioning.
• Computed tomography (CT) scan, which uses a combination of X-rays and computer technology to examine bones and produces cross-sectional images ("slices") of the body.
• Magnetic resonance imaging (MRI), which uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of organs, soft tissues, muscles, ligaments and other structures within the body. Your child is exposed to no radiation during an MRI.
• Hip arthrography, which uses X-rays and dye injected into the joint to show the soft tissues (ligaments, tendons, cartilage and muscles) of the joint.
• Ultrasound, which uses sound waves to produce images of organs and soft tissues inside the body.

Imaging tests can identify what type of proximal femoral focal deficiency your child has — information that is critical to determining which treatment options will produce the best results for your child.

Types of PFFD

Several classification systems exist detailing different types of congenital anomalies of the femur. Most are based on imaging tests alone, but some also consider clinical presentation. 

The most widely used classification system divides proximal femoral focal deficiency into four types that include:

• Type A — The femur bone is slightly shorter on the proximal end (near the hip), and the femoral head (the ball of the thigh bone that goes into the hip socket) may not be solid enough to be seen on X-rays at birth, but later hardens (ossifies). This deformity is sometimes called congenital short femur, because the child’s anatomy from hip to knee is contiguous and similar to their peers except for the one shortened bone. In some cases, children with type A deformities will also have an externally rotated femur, which could lead to bowing of the legs (genu varum).
• Type B — The femur bone is shorter on the proximal end (near the hip) and the defect affects both the femoral head (the ball) and the femoral shaft (the long part of the bone). This defect is more severe than type A deformities because it will not heal spontaneously and, at skeletal maturity, the proximal femur (lower part near the knee) will not connect with the femoral head.
• Type C — The entire top half of the femur bone is absent, including the trochanters (the part of the bone in which muscles are attached to the upper thigh), and the femoral head. In type C deformities, the proximal femur is not connected to the hip in any way. In fact, many children with type C deformities also have acetabular dysplasia, a condition in which the acetabulum (hip socket) is shallow, abnormally shaped, and oriented outward.
• Type D — This is the most severe form of proximal femoral focal deficiency, in which most of the femur bone is absent and only a small irregular piece of bone above the distal femoral epiphysis (the end of the femur bone at the knee) is present. In the pelvis, no acetabulum (hip socket) is present; instead the pelvic wall is flat on the affected side.

Treatment for proximal femoral focal deficiency

Treatment for proximal femoral focal deficiency is more complex than almost any other congenital limb deficiency, and must be individualized based on:

• The type of PFFD and severity of your child’s condition
• The condition and stability of your child’s hip, knee and foot
• Your child’s age, overall health and medical history

At Children’s Hospital of Philadelphia, a multidisciplinary team of pediatric orthopedic surgeons, nurses, prosthetists and physical therapists collaborate to create a customized treatment plan that may include staged surgeries, limb-lengthening procedures and prosthetics to address your child’s functional defects.

Children with severe PFFD may require a prosthetic to walk. Because of this, treatment is geared toward improving how your child’s body works with the prosthetic. The goal is to improve your child’s overall function so they can move and develop at a pace similar to their peers.

While the timing of treatment varies from child to child, in most cases it begins when your child turns 3 years old — allowing time for early bone to harden — and is completed by the end of high school, when most children have finished growing.

Limb-lengthening

The first important treatment decision that must be made is whether your child could benefit from limb-lengthening procedures. The most likely candidates to benefit are children with a congenital short femur (Type A PFFD).

To be eligible for limb lengthening, a child must have:

• A femur with a predicted discrepancy at skeletal maturity of usually less than 40 percent of the contralateral femur
• A stable hip, or one that can be made stable
• Good function and stability in the knee, ankle and foot

Limb lengthening typically includes surgery to cut the bone, and placement of an internal rod or external fixator to slowly stretch the limb as new bone forms. While traditional treatment includes external fixators, orthopedic surgeons at CHOP are using a new internal technique for limb lengthening that eliminates the need for pins and bulky external fixation frames. Depending on how fast your child’s bone grows; this limb-lengthening procedure can take months and may need to be repeated.

Your child’s physician will determine the timing and staging of limb lengthening.

Prosthetics

If limb lengthening is not appropriate for your child — either because their leg-length discrepancy is too great or because they will not tolerate the procedures — prostheses should be considered.

While most children with proximal femoral focal deficiency will need an above-the-knee prosthesis with a mechanical knee, others with a stable biologic knee may only need a below-the-knee prosthesis. Determining which type of prosthetic device is best for your child’s condition — as well as the best approach to properly fit the device — is the next important decision in your child’s treatment plan.

Initial treatment for children with PFFD should mirror normal development and begin when a toddler is ready to stand. The child is fitted with a custom-molded prosthesis that equalizes leg lengths but does not require surgical correction. In most cases, these prostheses are not large enough to accommodate flexing at both the knee and foot, so developmental growth can be slower. However, a custom-molded prosthesis that accommodates the child’s lower extremity is effective at allowing young children to move around and explore their space.

Additional surgical procedures

As your child grows, the importance of having both a functional knee and foot becomes more important. At this time, decisions must be made about which prosthetic type is most appropriate and which surgical approach will allow the prosthetic to fit optimally.

Additional surgical options include:

• Knee arthrodesis, in which the knee joint is fused to adjacent bones (femur and tibia) allowing for a longer and more stable leg that can be more easily contained within the prosthesis.
• Foot amputation, in which the leg is shortened to accommodate a mechanical knee and the end of the leg can be more easily contained within a prosthesis.
• Rotationplasty, in which the ankle assumes the function of a knee. To accomplish this, the limb is surgically cut, rotated 180 degrees and reattached. This allows for improved function due to the use of a biologic knee instead of a mechanical one, and the need for a below-the-knee prosthetic.
• Hip stabilization, in which the hip socket (acetabulum) and femoral head are surgically corrected to address varus deformity (outwardly turned legs) and bone fractures that won’t mend without intervention (pseudoarthrosis). This procedure is only appropriate for children with Type A or B deficiencies.
• Iliofemoral arthrodesis, in which the knee assumes the function of the hip. In this procedure, the femur is fused to the pelvis so when the child extends their anatomic knee, they are effectively moving their hip. This procedure, which is most often used for children with Type C and D PFFD, is often performed as part of a staged reconstruction with rotationplasty or foot amputation to allow for improved prosthesis fit and enhanced function.
• Hip/pelvic osteotomy, in which a shallow hip socket is reshaped to create better coverage of the ball of the thigh bone. This procedure is often used to treat acetabular dysplasia. During surgery, the surgeon cuts the bones in the hip joint, reorients them, and secures them in a new position.

Safety in surgery

Surgery can dramatically improve the long-term outcomes for your child with proximal femoral focal deficiency, but it can also be a stressful experience for you and your child.

At CHOP, we offer a wealth of resources that can help you and your child prepare for surgery. Additionally, we follow many best practices before, during and after surgery to decrease the risk of infection and increase positive outcomes. Our safety protocols have been so successful that many other institutions have adopted them.

To learn more, read how we make safety in surgery a top priority.

Follow-up care for PFFD

Most children with proximal femoral focal deficiency will need long-term follow-up care into adulthood. The staged nature of treatments requires ongoing monitoring and care to determine optimal timing for each phase and determine if treatments are working as planned.

At Children's Hospital of Philadelphia, we offer a wealth of ongoing support and services for your child and family at our Main Campus and throughout our CHOP Care Network. Our team is committed to partnering with you to provide the most current, comprehensive and specialized care possible for your child.

We recognize your child's pediatrician as an important part of the clinical team and provide regular updates on your child's progress. If continued care and monitoring is necessary long term, we will help transition your child's care to an adult orthopedic team.

Outlook

Long-term outcomes for children with proximal femoral focal deficiencies depend largely on the severity of the condition and how well the child responds to treatment. Some children may need several surgeries and have lingering issues as they grow. Many children treated for PFFD can live long, active and full lives.