What is limb-length discrepancy?
Limb-length discrepancy is a difference in size between the length of both arms or both legs.
Small differences in limb length are common. In fact, as many as a third of the population may have a 1 cm or less (less than ½ inch) discrepancy between their right and left legs. These slight differences are generally not noticeable and don’t require treatment. Differences in arm length are even less noticeable and rarely impact how the arm functions, requiring treatment.
However, larger leg-length discrepancies can have significant impact on how a child moves. Many children have a noticeable limp when walking, have difficulty running, hip or back pain, and cannot play or perform activities of daily living as easily as their peers.
Children with limb-length discrepancies are often born with the condition, although it may not be obvious to parents until the child begins to crawl or walk. Some children develop limb differences over time as a result of illness or injury.
Leg-length discrepancies that affect a child’s mobility will require treatment. If the difference in legs is small, an orthotic such as a shoe lift may be recommended. For children with more significant leg-length differences, surgery may be needed.
There are many causes of limb-length discrepancies including:
- Bone diseases or dysplasias, including Ollier disease (multiple enchondromas), neurofibromatosis and multiple hereditary exostoses.
- Infections in the bone that cause growth plate disturbances.
- Neurologic conditions, such as cerebral palsy, spasticity and paralytic disorders.
- Conditions that cause joint inflammation, such as juvenile idiopathic arthritis.
- Trauma or injury to a bone which can lead to the bone healing in a shortened position, or to grow faster than the unaffected side. This is more likely to happen with compound fractures that occur near or in the growth plates (physis disruption).
- Congenital conditions, such as clubfoot, developmental dysplasia of the hip, hemihyperplasia and proximal femoral focal deficiency, which affect the growth on one side of the body or in a specific bone, or lead to a “false impression” of discrepancy.
- A tumor — or surgery to remove a tumor — which can temporarily or permanently affect growth in nearby body parts.
In many cases, these conditions are present at birth, but the limb-length discrepancy may not become noticeable until later in childhood.
In some cases, the cause of limb-length discrepancy remains unknown.
Signs and symptoms
Limb-length discrepancies can occur in arms or legs, but the symptoms are more obvious — and treatment is often needed — when a child’s legs are affected.
The effects of leg-length discrepancies vary from child to child, but symptoms may include:
- Uneven sizes of the femur (thigh bone) and tibia (shin bone) are most often found, but the fibula (smaller bone in the lower leg) may also be affected.
- Walking difficulties, which can include limping, waddling or walking on the tip-toes of the shorter leg.
- Easily fatigued due to the extra effort it takes to move.
Limb-length discrepancies also carry an increased risk for other related conditions including low-back pain, osteoarthritis and scoliosis.
Testing and diagnosis
Limb-length discrepancies are often first suspected by parents who notice their child’s gait is abnormal, or by school nurses during routine scoliosis screening. These early indications should be followed by a formal examination by experienced clinicians who are experts in diagnosis of bone development issues in children.
At Children's Hospital of Philadelphia (CHOP), a trained pediatric orthopaedic physician will perform a complete medical history, physical examination and visual evaluation of your child. During the physical exam, the physician will observe how your child sits, stands, walks and moves. Children may compensate for a shorter leg by walking on their toes, flexing their knee or limping.
To help determine the extent of the limb-length difference, doctors may ask your child to stand barefoot on the floor, then place a series of wooden blocks under the shorter leg until the child’s hips are level. The blocks used are then measured to determine the difference between the two legs.
In most cases, additional imaging will be ordered to confirm the diagnosis, create baseline measurements of both legs, and guide treatment recommendations.
This may include:
- X-rays, which produce images of bones. X-rays of the legs are always taken, but X-rays may also be taken of the hand and hip to help doctors determine if your child has reached skeletal maturity or how much growth your child has left.
- 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.
Imaging studies and physical examinations may need to be repeated every six to 12 months while your child is growing to determine if the discrepancy is increasing or remaining the same.
Your child’s doctor will consider several factors when planning treatment including:
- The size of the limb discrepancy
- Your child’s age and development
- The cause of the limb-length discrepancy if known
Patients with limb length discrepancies that are mild (less than an inch) and do not have any limb deformity can typically be helped with nonsurgical treatment.
Treatment may include:
- Orthotics, such as a shoe lift, can be fitted to the inside of the shoe, or outside of the shoe. Shoe lifts can relieve back pain from small leg-length discrepancies and are easily removed if not effective.
- Ongoing observation (every six to12 months) may be the best option for children who have not reached skeletal maturity. Regular measurement can determine if the leg difference is increasing or remaining the same.
Surgical treatment for limb-length discrepancies is designed to:
- Slow down or stop the growth of the longer limb
- Lengthen the shorter limb
- Shorten the longer limb
Guided growth surgery (epiphysiodesis) is a way to temporarily or permanently halt the growth of the longer leg, giving the shorter leg a chance to catch up. During surgery, the orthopaedic surgeon makes small incisions on the lower thigh (femur) and upper shin (tibia) near the knee to access the open growth plates (physes). Then, either drilling of the growth plate or placement of small metal plates around the physes to permanently or temporarily slow or stop bone growth in that specific area is done.
If the metal plates are in place, it is important for patients to follow-up with their orthopaedic surgeon every three to four months to measure the leg differences and determine the best time to remove the plates. Once the appropriate correction is achieved, the metal plates are removed and your child’s leg should resume normal growth.
Lengthening the shorter leg is often the preferred method to treat limb-length discrepancies and allow your child to grow to their full height. In limb-lengthening surgery, a surgeon cuts the bone of the shorter leg, then applies either an external fixator or internal device to slowly lengthen the bone and correct the deformity.
At Children’s Hospital of Philadelphia, an experienced pediatric orthopaedic surgeon will discuss both external and internal limb-lengthening, the risks and benefits of each procedure, and recommend which procedure, if either, is best for your child.
External fixation is the traditional model of treatment, and has been used successfully for many years. After surgery to divide the bone, a scaffold-like frame is connected to the bones with pins. Lengthening begins about a week after surgery and is performed manually by either the patient or a family member turning a dial on the external fixator several times a day. The dial increases the space between the cut bones, allowing new bone to slowly form, while nearby muscles, soft tissue and skin adapts. The bone may be lengthened about 1 mm a day and about 1 inch per month.
While very successful, limb lengthening with an external fixator can be challenging for some patients who report difficulty finding comfortable ways to sleep and wear clothing, as well as soft tissue stiffness and scarring.
For these reasons and others, the lower extremity deformity team at Children’s Hospital of Philadelphia has been using a new internal technique for limb lengthening for the past several years. This approach, called the PRECICE® nail, uses a magnetically controlled intramedullary lengthening nail to allow for controlled lengthening of long bones without the need for external pins or wires.
The PRECICE nail is inserted into the intramedullary canal (center) of the affected bones, similar to the techniques used to treat long bone fractures. Through a small incision, the bone is then divided. After an appropriate waiting period (usually seven to 10 days) an external motorized magnetic remote-control device is placed on the limb for about three to four minutes, four times a day. This allows for controlled lengthening of the rod and bone. The limb is usually lengthened by ¼ mm, four to eight times a day.
Both internal and external lengthening will take several months to complete.
For patients who have reached skeletal maturity and have mild or moderate leg-length difference — no more than 3 cm in the thigh bone or 2 cm in the shin bone — doctors may recommend limb shortening to even the leg lengths.
In this procedure, the surgeon removes a section of bone from the middle of the longer limb, and inserts a metal rod, plate and screws to keep the bone in place as it heals. Limb-shortening surgery can affect the muscles of the leg and should not be used for significant leg-length discrepancies.
Amputation and prosthetic fitting
In rare cases, when the affected limb is substantially shorter (8 inches or more) and cannot be suitably reconstructed, or when limb-lengthening procedures cannot be tolerated by the patient, amputation and prostheses may be considered.
Depending on which bone is affected, doctors may recommend an above-the-knee prosthesis with a mechanical knee (femur deficiency), or a below-the-knee prosthesis (tibia deficiency).
Safety in surgery
Surgery can dramatically improve the long-term outcomes for your child with limb-length discrepancy, but it can also be a stressful experience for you and your child.
At Children’s Hospital of Philadelphia, we offer resources to 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 they have been adopted by many other institutions. Learn more about how we make safety in surgery a top priority.
No matter which treatment your child received, regular follow-up visits to your child’s doctor are recommended. Once the bone heals, your child will need physical therapy and rehabilitation to rebuild strength, endurance and coordination of both legs. Home exercises will likely be recommended.
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 orthopaedic team.
With proper treatment, children with limb-length discrepancies can live long, active and full lives.
Reviewed by Alexandre Arkader, MD