Children can be born with legs of different lengths. In other cases, injury or illnesses such as polio causes limbs to lengthen differently over time. It is possible for a slight difference in leg length to have no symptoms, however, a significant difference can make it difficult for a child to run and play.
Treatment depends upon the severity. In many cases, a minor difference in leg length can be evened out by wearing a lift in one shoe. A child with a more significant difference, however, may benefit from surgery to make their legs the same length. This can be done a number of ways, but is most often accomplished through a procedure that slows or stops growth in the longer leg.
A limb length difference may simply be a mild variation between the two sides of the body. This is not unusual. For example, 32 percent of military recruits in one study had a 1/5- to 3/5-inch difference between the lengths of their legs. This is a normal variation. Greater differences in length, however, can affect a patient's well-being and quality of life.
In most cases, the bones affected by a leg length discrepancy are the femur and tibia. Similar to the other long bones in the body, the femur and tibia do not grow from the center outward. Instead, growth occurs around the growth plates. Growth plates are areas of cartilage located between the widened part of the shaft of the bone and the end of the bone. If illness or injury damages the growth plate, the bone may grow at a faster or slower rate than the bone on the opposite side.
Previous Injury to a Bone in the Leg
A broken leg bone can lead to a limb length discrepancy if it heals in a shortened position. This is more likely to happen if the bone was broken into many pieces. It is also more likely to happen if the skin and muscle tissue around the bone were severely injured and exposed, as occurs in an open fracture.In a child, a broken bone sometimes grows faster for several years after healing, causing it to become longer than the bone on the opposite side. This type of overgrowth occurs most often in young children with femur (thighbone) fractures.
Alternatively, a break in a child's bone through the growth plate near the end of the bone may cause slower growth, resulting in a shorter leg.
Bone infections that occur in growing children may cause a significant limb length discrepancy. This is especially true if the infection happens in infancy.
Bone Diseases (Dysplasias) Certain bone diseases may cause limb length discrepancy, including: Neurofibromatosis, Multiple hereditary exostoses, Ollier disease
Other causes of limb length discrepancy include: Neurologic conditions, Conditions that cause inflammation of the joints during growth, such as juvenile arthritis
In some cases, the cause of limb length discrepancy is "idiopathic," or unknown. This is particularly true 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 limb length difference may be too small to be detected early on. As the child grows, however, the discrepancy increases and becomes more noticeable. In underdevelopment, one of the two bones between the knee and the ankle is abnormally short. The child may also have related foot or knee problems.
Hemihypertrophy (one side too big) and hemiatrophy (one side too small) are rare conditions that cause limb length discrepancy. In patients with these conditions, the arm and leg on one side of the body are either longer or shorter than the arm and leg on the opposite side. There may also be a difference between the two sides of the face. In some cases, the exact cause of these conditions cannot be determined.
The effects of limb length discrepancy vary from patient to patient, depending on the cause and size of the difference.
Patients who have differences of 3-1/2 to 4 percent of total leg length (about 4 cm or 1-2/3 inches in an average adult) may limp or have other difficulties when walking. Because these differences require the patient to exert more effort to walk, he or she may tire easily.
Some studies show that patients with limb length discrepancies are more likely to experience low back pain and are more susceptible to injury. Other studies do not support this finding, however.
For patients with minor limb length discrepancies (less than 1 inch) and no deformity, treatment is usually nonsurgical in nature. Surgical treatment to equalize small differences in leg length is not usually recommended.
In general, surgeries for limb length discrepancy are designed to do one of the following:
- slow down or stop the growth of the longer limb,
- shorten the longer limb, or
- lengthen the shorter limb.
In children who are still growing, epiphysiodesis can be used to slow down or stop growth at one or two growth plates in the longer leg.
It is a relatively simple surgical procedure that can be performed in one of two ways:
Metal plates with screws can be placed around growth plates in both the femur and tibia to temporarily restrict growth.
The growth plate may be destroyed by drilling or scraping it to stop further growth. The leg length discrepancy will gradually decrease as the opposite leg continues to grow and "catch up."
Metal staples, or a metal plate with screws, may be placed around the sides of the growth plate to slow or stop growth. The staples are then removed once the shorter leg has "caught up."
The procedure is performed through very small incisions in the knee area, using x-rays for guidance. Proper timing is critical. The goal is to reach equal leg length by the time growth normally ends—usually in the mid to late teenage years.
Disadvantages of epiphysiodesis include: The possibility of a slight over- or under-correction of the limb length discrepancy, The patient's adult height will be less than if the shorter leg had been lengthene, Correction of a significant discrepancy using this technique may make the patient's body look slightly disproportionate because of the shorter leg.
In patients who are finished growing, the longer limb can sometimes be shortened to even out the leg lengths.
To do this, the doctor removes a section of bone from the middle of the longer limb, then inserts metal plates and screws or a rod to hold the bone in place while it heals.
Because a major shortening may weaken the muscles of the leg, limb shortening cannot be used for significant limb length discrepancies. In the femur (thighbone), a maximum of 3 inches can be shortened. In the tibia (shinbone), a maximum of 2 inches can be shortened.
Because of their complexity, limb lengthening procedures are usually reserved for patients with significant discrepancies in length.
Lengthening can be performed either externally or internally.
In this procedure, the doctor cuts the bone in the shorter leg into two segments, then surgically applies an "external fixator" to the leg. The external fixator is a scaffold-like frame that is connected to the bone with wires, pins, or both.
The lengthening process begins approximately 5 to 10 days after surgery and is performed manually. The patient or a family member turns the dial on the fixator several times each day.
When the bones are gradually pulled apart (distracted), new bone will grow in the space created. Muscles, skin and other soft tissues will adapt as the limb slowly lengthens.
The bone may lengthen 1 mm 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 of growth. Factors such as age, health, smoking and participation in rehabilitation can affect the amount of time needed.
External limb lengthening requires: Meticulous cleaning of the area around the pins and wires, Diligent adjustment of the frame several times daily.
Potential risks and complications of external lengthening include:
- infection at the site of wires and pins
- stiffness of the adjacent joints
- slight over- or under-correction of the bone's length.
In this procedure, the doctor cuts the bone in the shorter leg, then surgically implants an expandable metal rod in the bone. The rod is completely internal and lengthens gradually in response to the normal movements of the patient's limb.
As the rod lengthens, the bones are gradually pulled apart and new bone grows in the space created. The rod provides stability and alignment to the bone as it lengthens.
Because no external fixator is used in internal lengthening, there is less risk of infection—including the superficial infection that commonly occurs around pin sites.
Internal lengthening avoids the physical and psychological challenges that come with wearing an external fixator; however, it allows for less precise control over the rate of lengthening.
Both internal and external lengthening take several months to complete. Both procedures require:
- regular follow-up visits to the doctor's office
- extensive rehabilitation, including physical therapy and home exercise