The human body looks symmetrical, with the body parts on the left side matching up to their counterparts on the right—two eyes, two arms, two legs. But many of those parts aren’t an exact match. One eye could be larger than the other; one limb could be longer than the other.
“We’re all asymmetric to some degree,” says UNC Health pediatric orthopedic surgeon Anna Vergun, MD. “It’s easiest to see it in faces, but it’s the same with limbs.”
It’s estimated that more than half of people have one leg longer than the other, but it’s not always a cause for concern.
“Limb-length difference becomes clinically significant when there’s more than a 2-centimeter difference in the lower extremities of an average height person, average height being about 5 feet, 5 inches,” Dr. Vergun says.
Two centimeters is less than the diameter of a quarter, so you might not see or notice a very small leg-length discrepancy, but even a modest difference can affect how you move. Dr. Vergun explains how these discrepancies occur and what treatments your doctor might consider.
Short Leg: Causes of Leg-Length Discrepancy
A leg-length discrepancy may be obvious from the time you are born, or it may have become noticeable as you grew throughout childhood.
“There’s a long list of things that can cause one side of the body to grow at a faster rate, or one side to grow at a slower rate,” Dr. Vergun says. “There could be neurologic causes, like a stroke or cerebral palsy. There could be a genetic difference at the limbs or a growth plate issue.”
Fractures or other injuries can cause a discrepancy, as can treatment for hip dysplasia, a congenital condition in which the bones of the hip joint don’t fit together. Limb-length differences can be caused by bone infections or bone diseases.
“It’s also common to have an idiopathic discrepancy, in which nothing else is wrong,” Dr. Vergun says. “In children, it can look like a very small difference, but it can get larger as they get bigger.”
Diagnosing Leg-Length Discrepancy
For children with leg-length discrepancy, a parent or pediatrician may notice irregularities in a child’s walk; they may flex one knee differently, limp, or walk on their heels or toes on one foot to compensate for the difference. Sometimes, these changes to the gait can cause joint pain or affect the child’s energy level because one side of the body is doing more work.
No matter your age, your doctor can confirm a discrepancy with a physical exam, which allows them to identify which part of the leg (above or below the knee) is affected. Dr. Vergun says a typical exam would involve lying flat on a firm surface, with the doctor putting your legs in various positions for evaluation. You might also get X-rays or other scans.
The doctor will then measure the length of the discrepancy, but Dr. Vergun says this measurement can be challenging if you or your child have other skeletal issues, such as an asymmetrical pelvis or a curved spine due to scoliosis. There may be variabilities between providers, so it’s helpful to have a doctor experienced in the condition do the measurement.
Treatment Options for Leg-Length Discrepancy
The measurement of the discrepancy matters because that will dictate the treatment options. With children, doctors will use the current measurement and project what the difference will be when they finish growing. For example, a 2-year-old with a 3-centimeter leg-length difference would likely have an 8-centimeter difference after typical growth, so their treatment plan would be based on that 8-centimeter difference. If the person has finished growing, the doctor can use the current difference.
“For a person of average height, with a discrepancy of 0 to 2 centimeters, we typically don’t recommend any treatment other than a shoe lift on one side,” Dr. Vergun says. “For a person with a discrepancy of 2 to 5 centimeters, there are ways to shorten the longer side through a shortening surgery, or by stopping the growth in the growth plate of the longer leg so that limb length equalizes as they grow.”
This process of stopping growth at the growth plates is known as epiphysiodesis. For children who are still growing, surgeons can drill, scrape or place implants on the tissues at the end of bones that determine growth. It’s less invasive than the surgery required to cut and shorten a bone, but requires good prediction of the ultimate discrepancy.
Dr. Vergun says doctors consider leg-lengthening procedures for discrepancies of more than 5 centimeters (slightly less than 2 inches).
“In a lengthening procedure, we cut the bone of the shorter leg and slowly distract, or pull, the bone away from where it was cut, letting the body work to heal the bone like it would a fracture,” she says. “We can pull that bone about a millimeter, half millimeter, per day.”
There are different ways to do that pulling, which Dr. Vergun says will depend on the patient’s age and situation. It’s most commonly done by placing an external fixator or frame on the leg after the cut; you turn a dial on the frame to slowly pull the bone away from where it was cut, which forces the bone to lengthen as it heals. It can also be done by placing internal rods alongside the bone that are pulled by an external magnet.
Leg lengthening can be difficult for the patient and their family, due to the time and attention needed to complete the process, and complications can include issues with nearby joints, tendons and nerves. Your doctor can provide more information on the age that this procedure might be most appropriate.
When Leg-Length Discrepancy Goes Untreated
Leg-length discrepancy doesn’t always need to be treated. Even though a discrepancy can change your gait, that doesn’t necessarily mean that you’ll eventually have hip, knee or back pain.
“I have many patients with large discrepancies who are pain-free and doing quite well,” Dr. Vergun says. “People can be focused on a discrepancy being the source of their joint pain, but very rarely is it the source or only cause.”
Dr. Vergun says that major studies have not found an increase in incidence in hip or back pain in people with limb-length discrepancies of less than 4 centimeters.
“That’s not to say those people don’t have those problems—hip and back pain are very common—but we don’t see increased incidence because of the difference in the limbs,” she says. “I do know that for some patients with small differences who are having symptoms related to pain, you can put in a heel lift and they will feel better.”
If you or your child are feeling pain and you’re concerned that it’s due to a leg-length discrepancy, Dr. Vergun recommends talking to your doctor.
“There are simple things we can do, like trying a shoe lift to see if pain gets better,” Dr. Vergun says. “It’s important to be seen and get help teasing out where that pain may be coming from.”
If you’re concerned about your child’s growth or pain in your own joints, talk to your doctor. Need a doctor? Find one near you.