Limb Length Inequality

Most people have arms or legs that are different lengths. In fact, it is normal for leg lengths to be different by as much as one centimeter. Leg length discrepancy is more common than arm length discrepancy. A problem arises when the discrepancy between leg lengths is larger and causes symptoms, and equalization of leg lengths is an important part of our practice.

The most common reason for unequal bone length is “idiopathic limb length inequality,” which means we don’t know why it occurred. This is usually congenital, which implies the child was born with this problem. Other reasons why one side may be longer or shorter than the other are trauma, infection, tumor or blood supply problems that can stimulate or inhibit growth.

Bones usually grow very predictably, and by getting an x ray that measures the leg bones accurately, we can predict how long a child’s legs will be when they are done growing. Knowing how large the discrepancy will be when the bones are mature helps us decide which treatment, if any, will be necessary. All children stop growing when they reach a bone age of 16, but not all children will reach a bone age of 16 on their 16th birthday. Because children’s bones mature at different rates, some children will stop growing earlier than others. This is why the bone age is so important in determining what treatment your child will get, and when it should be done.

The treatment of leg length discrepancy depends on the size of the discrepancy and the age of your child. Eventually we want the leg lengths to be within a centimeter of each other. Everyone’s legs are a little “uneven,” and no treatment is necessary for discrepancies of a centimeter or less, since this degree of discrepancy rarely causes any symptoms. When your child is young, we will follow the discrepancy to make sure we know exactly how big the difference will be when your child stops growing. If the discrepancy is not causing symptoms, we will probably not treat it. We may decide to see your child again to make sure the discrepancy doesn’t get bigger, but we don’t usually recommend a lift, insert or any other device to treat a small discrepancy.

Discrepancies that are larger will need to be followed to ensure they do not get over two centimeters (about an inch). We know that discrepancies less than two centimeters do not cause symptoms in most people. Even though there are some people who will use a lift for a this discrepancy, there are millions of people who do not use a lift for that same amount of discrepancy and have no problems.

If the discrepancy will eventually be over 2 centimeters, it will require treatment while your child is growing. For those that will be between 2 and 4 centimeters the best option is often slowing the growth of the long leg. This is called Epiphyseodesis. For discrepancies that are longer than 4 centimeters, or for certain patients with smaller discrepancies, we consider the option of limb lengthening.

Treatment

The treatment of limb length inequality is mostly surgical. For small discrepancies, we can put a lift into the shoe, up to about one centimeter. It is hard to get the foot into the shoe if the lift is thicker than one centimeter. We can also put a lift on the outside of the shoe, but after about two centimeters the shoe begins to get clumsy and unstable, like a platform shoe. When possible, we try to use inside lifts and not outside lifts, since children seem to like them better. We still have not found a way to lengthen limbs by using magnets, manipulation or other therapies, but hopefully someday we will find a non-operative therapy that will be effective.

Epiphyseodesis is the procedure used to stop or slow the growth of the longer leg to allow the shorter one to “catch up.” It is a simple and accurate and is usually done as an outpatient procedure that takes about an hour. Once we have calculated what the size of the discrepancy will be when the legs are done growing, we can stop the long leg from growing when the short leg has that much left to grow. For example, if we calculate that the discrepancy will be three centimeters, we can stop the growth of the long leg when the short leg has three more centimeters to grow. This allows the short leg to keep growing and end up the same length. The goal with this method is to get the leg lengths to within a centimeter since we know that a discrepancy of a centimeter or less usually doesn’t cause any symptoms.

Bones grow longer at the growth center, known as the physis. The physis is made of cartilage and is found at the end of the bones, sandwiched between two layers of bone. The bones get longer because the cartilage grows and turns into bone. Epiphyseodesis involves anesthetizing the area so it doesn’t hurt, then making a small incision so we can go into the knee with a drill or scraper to scoop out some cartilage. Sometimes a staple is placed across the growth center, which also slows the growth. By stopping the cartilage from growing, the bone will not get longer and the shorter leg can catch up. This method is about 90% successful.

There are two potential problems with Epiphyseodesis – first we have to be very careful and accurate in the calculation of length predictions. Since the methods we use have been around for many years and have been tested on hundreds of children, we can usually feel confident in these predictions. The second possible problem is that the procedure can slow the growth but not stop it. We then use other methods to make the legs even.

After the surgery, your child will wear a soft splint called a knee immobilizer and will be asked to put only minimal weight on the leg for three weeks. Because bearing too much weight can cause the leg to break, your child will need to use crutches, should not stand on the leg, and should keep the immobilizer on snug during the day. At night and for baths, the immobilizer can be removed. Your child will need help with bathing and getting around until they are comfortable and the leg is strong enough to hold up.

The other way to approach the problem of limb length discrepancy is limb lengthening. Lengthening bones has been attempted for centuries but has not always been successful. In the early 1900’s, one method was to cut the bone, move the cut ends apart and screw them in place. Often the bone would not heal. Another method was to cut the bone and place the patient in traction, pulling on the leg to pull the cut ends apart and lengthen the bone. This did not always allow the bone to heal straight.

During World War II in Siberia, a surgeon named Gavril Ilizarov developed a method of placing small pins in the bone, waiting for a while, then gradually stretching the bone and allowing the cells in the bone to heal slowly, as if stretching a healing fracture. This method, called Distraction Osteogenesis, is the method we use today. Surgeons in the Bay Area were also pioneers in this method, including a Dr. Abbott, who in 1927 suggested waiting after cutting the bone before starting to lengthen it.

Limb lengthening by the Ilizarov method works beautifully, and can be accomplished in many ways and with many types of devices. All the methods involve a surgery to place pins and wires in the bone, cutting the bone through a small incision, attaching the pins and wires to an apparatus on the outside of the leg called an external fixator, and then, after about a week, you begin lengthening the bone at home. The process of lengthening can take a long time, since the bone can only grow by a millimeter a day, and it must be lengthened each and every day. You and your child will turn four to six “clickers” on the apparatus every day. It is not painful, but some kids say it feels “tight.”

Broken bones heal by forming a matrix of bone cells at the break, called a callus. In Distraction Osteogenesis the bone reacts in the same way, except that every time it tries to calcify the healing bone, it gets pulled apart another millimeter. When the leg is at the desired length, you will stop lengthening and we allow the callus to harden. With this method, the leg can be lengthened about a centimeter per month.

There is a new method that has recently been introduced that involves placing a rod inside the bone that lengthens as you move your leg and walk around. It is not difficult to put rods inside of bones, and we often put rods inside bones for other reasons. This method requires a large bone, a patient who is almost done growing and is more complicated than the Ilizarod method. We hope that in the future we can do more limb lengthening with this method, instead of using pins and wires. (back to the top)

Frequently Asked Questions

How can you calculate the length of legs when the child is done growing?

The bones in the legs grow very predictably. We know how much growth to expect from each of the growth centers at the hip, knee and ankle. The most important of these growth centers is around the knee, and we know that the lower end of the thigh bone, or femur, grows about one centimeter per year while the upper end of the shin bone, or tibia, grows about 6 millimeters per year. If we have accurate measurements of the bone lengths, and know when the legs will stop growing, we can determine the final lengths of each leg and calculate what the discrepancy will be between the two legs. (back to the top)

If everyone’s leg bones grow at the same rate and stop growing at the same bone age, why aren’t everyone’s legs the same length?

Skeletal age does not always equal bone age. All children will stop growing when their bones reach a bone age of 16 years. How old they are chronologically (that is, how many candles are on their birthday cake) is not necessarily the same as their bone age. It is possible to reach a bone age of 16 when you are 12 years old. Usually these people will be short, since they have stopped growing relatively early. Some people don’t reach skeletal maturity, or a bone age of 16, until they are 20 years old, and as a result of all those “extra” years growing, will be quite tall. (back to the top)

How do you calculate bone age?

Bone age is best measured by an x ray of the hand and wrist. Many years ago, a catalog was made of hand x rays at different chronologic ages. By comparing all 27 bones in the hand and wrist at different stages of maturity, we can arrive at a good estimate of your bone age, and how many years of growth you have left before reaching skeletal maturity at bone age of 16 years. (back to the top)

How do you measure the leg bones accurately?

We sometimes measure the legs using a tape measure, though this is quite inaccurate. Other ways to measure the legs clinically are to compare the height of the pelvis while standing or while standing on measured blocks. The best way to measure the leg bones, though, is to use an x ray method. Because we like to avoid doing x rays whenever possible, we do not do this every time, only when we need to get an accurate measurement.

One of the best x ray methods is called a CT Scanogram. This is a painless and quick procedure that exposes the child to less radiation than they would be exposed to flying in a plane. This x ray gives us accurate measurements of the lengths of all the bones in the leg. At the same time, we get a bone age x ray so that we can interpret the length data and predict how much growth is left. (back to the top)

How often do you need to check x rays to predict the final leg length discrepancy?

We don’t need to overdo it by getting x rays every year. After getting two sets of scanograms and two bone age x rays, we can accurately determine what the child’s eventual length discrepancy will be, and decide what to do about it. We are very careful to collect good data, and if we are not satisfied with the scanogram we will repeat it. Sometimes, we may want even more than two sets of data to be very accurate in our predictions. (back to the top)

Won’t a discrepancy hurt my child?

Childhood discrepancies and small adult discrepancies will not have any effect. Think about how many hours a day a child spends off their feet – sitting, sleeping, jumping and swinging. During these activities, the limb length discrepancy has no effect. While walking, there is no time during the walking cycle when the legs are together evenly on the ground. One leg is always in front, and the other behind. The pelvis is uneven then anyway. There may be a small increase in waddling while walking due to the leg length discrepancy, but it will not have a long term impact on the spine, it will not cause a curve in the spine or scoliosis, and will not cause back pain. The child who looks uneven can have a lift placed in the shoe to help improve their appearance and gait.

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