When Your Child Has Leg-Length Discrepancy (LLD)

Your child has been diagnosed with a leg-length discrepancy (LLD). This means that your child's legs are slightly different lengths, with one leg longer than the other. The difference in lengths can vary widely. The larger the difference in lengths, and the younger the child, the more problems that can result as the child gets older. Because of this, your child may be referred to a pediatric orthopedist. This is a doctor specializing in treating bone and joint problems in children.

LLDs are very common. Sometimes the cause isn't known. But the known causes of LLD in children include:

• Injury or infection that slows the growth of a leg bone
• Injury to the growth plate. This is a soft part of a long bone that allows the bone to grow. Growth plate injury can slow bone growth in that leg.
• A break or fracture to a leg bone that causes overgrowth of the bone as it heals
• A problem that is present at birth (congenital). For example, a whole side of the child's body may be larger than the other side.
• Conditions that affect muscles and nerves, such as polio

• The doctor carefully examines the child. They check to be sure the legs are actually different lengths. This is because problems with the hip (such as a dislocated joint) or back (scoliosis) can make it seem like a leg is shorter, when both legs are the same length.
• An X-ray of the child's legs is taken. During the X-ray, a long ruler is put in the image so an accurate measurement of each leg bone can be taken. Sometimes a CT scan is done.
• If an underlying cause of the discrepancy is suspected, more tests are done to further evaluate.

Treatment for an LLD depends on the amount of difference and the cause, if known. The doctor will discuss treatment choices carefully with you and your child before any decisions are made. Treatment is planned with your child's final height and leg lengths in mind, not the current leg lengths.

Treatment is generally not needed if the child's final LLD is predicted to be 2 centimeters (cm) or less at full height. But the child should be checked regularly by an orthopedist.

Treatment is often advised for LLDs predicted to be more than 2 cm at full height. If treatment is done, it often doesn't begin until the child starts walking. Possible treatment choices include:

• A “lift” in a shoe to level the child's hips. An orthopedic shoe insert or lift is often the only treatment needed for small discrepancies.
• Surgery to shorten the longer leg. This is less complicated than lengthening the shorter leg. Shortening may be done by:
  • Closing the growth plate of the long leg, letting the short leg catch up as the child grows. This procedure is called an epiphysiodesis. Your doctor will determine the best timing for the surgery based on how much your child is still likely to grow, and how much difference in leg length is expected by the time they are finished growing.
  • Or taking some bone from the longer leg, once growth is complete, to even out leg lengths.
• Surgery to lengthen the shorter leg. This surgery is more complex than surgery to shorten a leg. During this surgery, the bone is cut into two pieces. Then the lengthening device is put in place. In external lengthening, the device is a metal frame on the outside of the leg, attached through the skin to the bone. In internal lengthening, the device is a metal rod inserted into the bone. In either case, the device is very slowly lengthened and the bone gradually gets longer. The device is removed at the end of treatment, usually after several months. This surgery requires careful and continued follow-up with the surgeon to be sure that healing is going well.

Physical therapy for strength and flexibility is an important part of treatment. This is especially helpful after surgery.

A child with an LLD often has no activity restrictions. Treatment often leads to a good result. If a larger LLD is not treated, back, hip, and knee problems often occur as the child grows.