 Leg Length Discrepancy
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If one of your child's legs is longer than the other leg, he or she has a common problem known as leg length discrepancy. A typical difference in leg length can be anywhere from 1 centimeter, which usually does not cause any problems, to more than 6 centimeters. The greater the discrepancy, the more a child must compensate his or her normal posture and gait (walking pattern) in day to day life, which can lead to a variety of symptoms, such as functional scoliosis, hip, knee and ankle problems.
There are generally two kinds of leg length discrepancies.
- Structural discrepancy occurs when either the thigh (femur) or shin (tibia) bone in one leg is actually shorter than the corresponding bone in the other leg as a result of a condition that has either caused one bone to be shorter than normal or longer than normal.
- Functional discrepancy occurs when the leg lengths are equal, by symmetry is altered somewhere above the leg, which in turn disrupts the symmetry of the legs. For example, developmental dislocation of the hip can cause a functional discrepancy. In DDH, the top of the leg bone (femur) that is not properly positioned in the hip socket may hang lower than the femur on the other side, giving the appearance and symptoms of a leg length discrepancy.
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The causes of a leg length discrepancy, even the most common ones, are numerous and varied. A discrepancy can result from an injury, such as in a fracture that damages the cells responsible for growth of the bone, while the corresponding bone on the other leg grows normally. Some fractures can also lead to overgrowth of bone during the healing process, resulting in a longer than normal bone. Overgrowth commonly occurs in young children with femoral fractures.
Diseases of the bone, such as osteomyelitis, can injure a region in a bone, called the growth plate, where growth in length occurs, so that a discrepancy occurs gradually over time.
Some children are born with legs that are of unequal length or bowed tibias that are accompanied with a leg length discrepancy. Functional leg length discrepancy can also result from congenital (present at birth) problems, that alter alignment of the hips, such as coxa vara and developmental dislocation of the hip. Neuromuscular problems, such as cerebral palsy, which causes problems with alignment and posture can also lead to a functional discrepancy.
Bone tumors and treatments designed to irradicate them are related to leg length discrepancy. Tumors can invade the bone's growth plate like an infection and treatments, like chemotherapy, can also damage the plate.
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The symptoms of a leg length discrepancy vary widely and are often related to the underlying problem causing the discrepancy and the alignment problems that result from it. Keep in mind that every child experiences symptoms of this condition differently. Always consult a physician for a diagnosis.
The following are symptoms of a leg length discrepancy:
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one leg is obviously shorter than the other (although this is not always obvious)
problems with posture (i.e. shoulder may tilt toward shorter side) leading to compensatory or functional scoliosis.
- gait problems, such as limping, toe-walking, or rotation of the leg.
a knee that's chronically hyperextended on the short side and flexed on the long side.
- pain in the back hip, knee, and/or ankle
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Diagnostic procedures include a complete medical history of the patient and a physical examination by an orthopaedic surgeon. The doctor will use both of these tools to determine the underlying cause of the problem.
During the physical exam, your child's doctor will probably take two measurements of your child's legs with a tape measure. One measurement, to determine the "real" length of the leg will be taken from the middle of the hip down to the ankle. The other, the "apparent" length, will be taken from the naval area. The discrepancy determined by these two measurements might be different if the "apparent" length is affected by hip position, suggesting a functional discrepancy.
The doctor may also ask your child to stand with a block under the shorter leg to confirm the measurement estimate the amount of correction that feels best. The doctor will also want to confirm the measurement with the following diagnostic tests:
- X-rays - a diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film. This is used to obtain an accurate measurement of leg length discrepancy.
- Computerized tomography scan (also called a CT or CAT scan) - a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce cross-sectional images (often called "slices"), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general X-rays.
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Specific treatment for leg length discrepancy will be determined by your child's orthopaedic surgeon based on:
- your child's age, overall health, and medical history
- the extent of the discrepancy
- your child's tolerance for specific medications, procedures, or therapies
- expectations for the course of the condition
- your opinion or preference
You and your child's feelings about the treatment are extremely important. Some techniques used to equalize leg length are simple and safe, but others, especially lengthening procedures, are complex with high complication rates. These require strict cooperation by child and parents for success.
Much planning is involved in the early stages of managing a child with a leg length discrepancy. Since children are still growing, the goal of treatment is to correct the discrepancy that would be present at maturity and not the present discrepancy. To complicate matters, not all children grow at the same rate, so careful analysis of your child's personal rate of growth is crucial. To estimate the discrepancy at maturity, your child's orthopaedic surgeon may need to continually take measurements of your child's growth over a period of one or two years before any surgery can be considered.
The goal of treatment is not always to have legs of equal length. For example, some patients, with neuromuscular conditions that involve muscle weakness or paralysis of the short leg, may do best with an undercorrection of 1 or 2 cm. This slight discrepancy allows for clearing of the floor during the swing phase of the walking cycle.
Generally speaking, discrepancies greater than 2 cm at skeletal maturity usually require some kind of intervention, because these will cause limping. The following are treatments used to correct discrepancies:
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- Orthotics: A shoe lift can be used to treat discrepancies from 2 to 6 cm. The lift should be large enough to allow the patient to walk normally.
- Prosthetics: These devices, which are typically used to treat a child who has had to have an amputation, may be satisfactory for some patients with very large discrepancies, who would not benefit from other lengthening or shortening procedures.
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- Shortening procedures: The following procedures, used to shorten the longer leg, may be recommended for some children, in cases where the leg length discrepency is expected to be between 2 and 6 cm at maturity. Shortening is considered safer and results in less complications than lengthening procedures:
- Epiphysiodesis - This procedure slows the rate of growth of the long leg, allowing the short leg to catch up. The operation involves the creation of bony ridge, usually by repositioning a block of bone in the region, that tethers the growth plate, preventing future growth. The disadvantages of this procedure include shortened stature, surgery on the unaffected extremity, and the irreversibility of the procedure.
- Epiphyseal stapling - This operation is performed to slow the rate of the growth temporarily. Staples are surgically inserted on each side of the growth plate. Once equalization has been achieved, the staples are removed.
- Bone resection - This operation, removal of a section of bone to equal out the discrepancy, can be performed in adults or adolescents who are no longer growing.
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- Lengthening procedures are usually reserved for discrepancies that are more than 4 cm. While one of the obvious advantages of lengthening is the achievement of a desirable height, it is not always the method of choice because the process used is technically difficult and has a significant rate of complications, discussed further below.
For this procedure, a customized apparatus that encircles the leg is surgically attached to the limb that will be lengthened by pins. Limb lengthening correction works on the principle of bone regeneration (osteogenesis) as segments of the bone are pulled apart (distracted). To achieve this, a bone is first cut in two during surgery. Days after surgery, the two ends of the bone are very gradually pulled apart through continual adjustments that are made to the apparatus, usually at a rate of 1 mm per day. This gradual distraction leads to formation of new bone between the two ends, at the site of lengthening. After the process in complete, and the bone is given a chance to harden, the apparatus is surgically removed. A cast or brace may be required for some time for further protection
Common complications associated with lengthening procedures include pin tract infection, wound infection, hypertension, partial dislocation of the hip and knee, a delayed union of the bone and fatigue fractures after removal of the lengthening apparatus.
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Physical therapy, designed to stretch muscles and maintain joint flexibility, is an important component to any surgeries used to correct leg length discrepancies.
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With the proper treatment, rehabilitation and follow-up care, children with a leg length discrepancy go on to do very well and are soon able to resume all of their normal activities with no restrictions.
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