What is limb-length discrepancy?

Limb-length discrepancy is a difference in size between the length of both arms or both legs. 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.

Treatments for limb-length discrepancy

Nonsurgical treatment

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

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

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.

Limb lengthening

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.

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 (CHOP) 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.

Limb shortening

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).