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. A normal variation of approximately 0.5 to 1.5 cm difference between the length of the legs is acceptable. 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 leg bone fracture may lead to a limb length discrepancy if the healing process occurs in a shortened position. This is more likely if the bone was broken in many pieces. The likelihood of this event is also greater in case the skin and muscle tissue around the bone were severely injured and exposed, as in an open fracture.
In children, broken bones sometimes have a faster rate of growth then the uninjured bone, and this happens for several years after healing, causing the injured bone to become longer. On the other hand, if the fracture falls through the growth center near the end of the bone, this may result in slower growth and thus a shorter leg.
Bone infections that occur in children during the active growth phase may cause a significant limb length discrepancy. This is particularly if the infection happens in infancy (during the 1st year of life). 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.
Other causes include inflammation (arthritis) and neurologic conditions
Sometimes the cause of limb length discrepancy cannot be identified. This is seen especially in cases where there is underdevelopment of the inner or outer side of the leg, or partial overgrowth of one side of the body. These conditions are usually noted at birth, but the leg length difference may not be large enough and so goes undetected. As the child grows, the limb length discrepancy increases and becomes more obvious. 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.
Certain rare limb length discrepancy conditions, including hemihypertrophy (one side too big) or hemiatrophy (one side too small), also involve limb length discrepancy. 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.
Limb length discrepancy can be measured by a physician during a physical examination, and on X-rays.
The level of the hips is measured when the patient is standing barefoot. A series of measured wooden blocks may be placed under the short leg until the hips are level. If the physician decides that a more precise measurement is needed, X-rays may be requested. 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.
Although limb length discrepancy may be detected on a screening examination for curvature of the spine (scoliosis), limb length discrepancy by itself does not cause scoliosis.
The extent of impairment caused by limb length discrepancy varies from one patient to another, 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 obvious abnormalities during walking; such differences may force the patient to exert more effort to walk.
The effect of limb length discrepancy on back pain remains a controversial issue. Some studies demonstrate that people with a limb length discrepancy are at a greater risk of suffering from 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 is usually not required. Because the risks may outweigh the benefits, surgical treatment to equalize leg lengths is usually not recommended if the difference is less than 2.5 cm. Such small differences are usually managed with 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 by a procedure that slows down the growth of the longer leg at one or two growth sites. The treating physician can give an estimate of how much equalization can be gained by this procedure.
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 7.5 cm can be shortened. In the shinbone, a maximum of 5 cm can be shortened.
Surgical lengthening of the shorter leg is another option.