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Differences between the lengths of the upper and/or lower arms and the upper and/or lower legs are called limb length discrepancies (LLD). Except in extreme cases, arm length differences cause little or no problem in how the arms function. This article, therefore, will focus on length differences in the legs.
A limb length difference may simply be a mild variation between the two sides of the body. This is not unusual in the general population. For example, one study reported that 32 percent of 600 military recruits had a 1/5 inch to a 3/5 inch difference between the lengths of their legs. This is a normal variation. Greater differences may need treatment because a significant difference can affect a patient's well-being and quality of life.
There are many causes of limb length discrepancy. Some include:
Previous Injury to a Bone in the Leg
A broken leg bone may lead to a limb length discrepancy if it heals in a shortened position. This is more likely if the bone was broken in many pieces. It also is more likely if skin and muscle tissue around the bone were severely injured and exposed, as in an open fracture.
Broken bones in children sometimes grow faster for several years after healing, causing the injured bone to become longer. A break in a child's bone through the growth center near the end of the bone may cause slower growth, resulting in a shorter leg.
Bone infections that occur in children while they are growing may cause a significant limb length discrepancy. This is especially true if the infection happens in infancy. Inflammation of joints during growth may cause unequal leg length. One example is juvenile arthritis.
Bone Diseases (Dysplasias)Bone diseases may cause limb length discrepancy, as well. Examples are:
- Multiple hereditary exostoses
- Ollier disease
Other causes include inflammation (arthritis) and neurologic conditions
Sometimes the cause of limb length discrepancy is unknown, particularly in cases involving underdevelopment of the inner or outer side of the leg, or partial overgrowth of one side of the body. These conditions are usually present at birth, but the leg length difference may be too small to be detected. As the child grows, the limb length discrepancy increases and becomes more noticeable. In underdevelopment, one of the two bones between the knee and the ankle is abnormally short. There also may be related foot or knee problems.
Hemihypertrophy (one side too big) or hemiatrophy (one side too small) are rare limb length discrepancy conditions. In these conditions, the arm and leg on one side of the body are either longer or shorter than the arm and leg on the other side of the body. There may also be a difference between the two sides of the face. Sometimes no cause can be found. This is known as an "idiopathic" difference.
Usually, the physician measures the level of the hips when the child is standing barefoot. A series of measured wooden blocks may be placed under the short leg until the hips are level. If the physician believes a more precise measurement is needed, he or she may use X-rays. In growing children, a physician may repeat the physical examination and X-rays every six months to a year to see if the limb length discrepancy has increased or remained unchanged.
A limb length discrepancy may be detected on a screening examination for curvature of the spine (scoliosis). But limb length discrepancy does not cause scoliosis.
The effects of limb length discrepancy vary from patient to patient, depending on the cause and size of the difference. Differences of 3 1/2 percent to 4 percent of the total length of the leg (about 4 cm or 1 2/3 inches in an average adult) may cause noticeable abnormalities when walking. These differences may require the patient to exert more effort to walk.
There is controversy about the effect of limb length discrepancy on back pain. Some studies show that people with a limb length discrepancy have a greater incidence of low back pain and an increased susceptibility to injuries. Other studies do not support this finding.
For minor limb length discrepancy in patients with no deformity, treatment may not be necessary. Because the risks may outweigh the benefits, surgical treatment to equalize leg lengths is usually not recommended if the difference is less than 1 inch. For these small differences, the physician may recommend a shoe lift. A lift fitted to the shoe can often improve walking and running, as well as relieve any back pain that may be caused by the limb length discrepancy. Shoe lifts are inexpensive and can be removed if they are not effective.
In growing children, legs can be made equal or nearly equal in length with a relatively simple surgical procedure. This procedure slows down the growth of the longer leg at one or two growth sites. Your physician can tell you how much equalization can be gained by this procedure. The procedure is performed under X-ray control through very small incisions in the knee area. This procedure will not cause an immediate correction in length. Instead, the limb length discrepancy will gradually decrease as the opposite extremity continues to grow and "catch up."
Timing of the procedure is critical. The goal is to reach equal leg length by the time growth normally ends. This is usually in the mid-to-late teenage years. Disadvantages of this option include the possibility of slight over-correction or under-correction of the limb length discrepancy. In addition, the patient's adult height will be less than if the shorter leg had been lengthened. Correction of significant limb length discrepancy by this method may make a patient's body look slightly disproportionate because of the shorter leg.
In some cases the longer leg can be shortened, but a major shortening may weaken the muscles of the leg. In the thighbone (femur), a maximum of 3 inches can be shortened. In the shinbone, a maximum of 2 inches can be shortened.
The bone may lengthen 1 millimeter per day, or approximately 1 inch per month. Lengthening may be slower in a bone that was previously injured. It may also be slower if the leg was operated on before. Bones in patients with potential blood vessel abnormalities, such as cigarette smokers, may also need to be lengthened more slowly.
The external fixator is worn until the bone is strong enough to support the patient safely. This usually takes about three months for each inch. Factors such as age, health, smoking and participation in rehabilitation can affect the amount of time needed.
Risks of this procedure include:
- Infection at the site of wires and pins
- Stiffness of the adjacent joints
- Slight over- or under-correction of the bone's length
- Regular follow-up visits to the physician's office
- Meticulous cleaning of the area around the pins and wires
- Diligent adjustment of the frame several times daily
- Rehabilitation as prescribed by the physician
A physician experienced in limb lengthening techniques can explain the treatment options and their risks and benefits in more detail. You and your physician can then decide what treatment, if any, is best for you.
Developed by the Limb Lengthening and Reconstruction Society and revised by a member of both the Limb Lengthening and Reconstruction Society and Pediatric Orthopaedic Society of North America
The American Academy of Orthopaedic Surgeons
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Rosemont, IL 60018