In a shocking triumph of statistics, 90% of human beings are born with one limb shorter than the other. While this difference is unnoticeable in most of the population, for others it can be detrimental to daily lifestyles and propagate other health challenges. Leg length discrepancy especially can lead to spinal problems and osteoarthritis if not corrected early on.
Defining Limb Length Discrepancy
When one limb (an arm or leg) is shorter than the other, the condition is classified as a limb length discrepancy (LLD). The disparity can range from a fraction of an inch to several inches, and while one extreme poses challenges and threat to overall health, any difference in limb length can present problems. Leg length discrepancies are more prone than differences in arm length to affect patients’ abilities to perform daily activities.
What Causes Leg Length Discrepancy?
Limb length discrepancies in the legs (also called lower limb length discrepancies) can arise based on many factors, both congenital and acquired. Some conditions, such as hemihyperplasia, cause bones or soft tissues on either side of the body to grow at different rates. Other diseases or conditions, usually vascular such as Klippel-Trénaunay-Weber syndrome, can produce this effect.
Such conditions, which cause one leg to grow longer than the other, are more rare than those which keep one leg relatively shorter. These may be behavioral or functional, including causes such as muscle contraction or deactivation, foot pronation or other imbalance, lumbar rotation, or imbalance of the pelvis. Some of these may in turn be caused by more structural difficulties such as an uneven pelvis, femur, or lumbar vertebrae.
A leg length discrepancy can also develop after an injury or illness. A serious fracture, or one that does not heal properly can result in different leg lengths, as can osteomyelitis or other bone infections or the presence of bone tumors or cysts.
Finding the Problem
Leg length discrepancy can only be properly treated once an accurate diagnosis has been made. Orthopedic testing is the primary method of diagnosis. This involves thorough observation of the alignment of the legs, low back, hip, and pelvis. A physician or chiropractor will have the patient stand with a board under the shorter leg and raise the board until the pelvis is level. Occasionally, specific X-ray testing may be required to determine if the bones are unevenly sized.
A Bit Off-Balance: The Dangers of Lower Limb Length Discrepancies
When it comes to length differences in the legs, the measurement matters. Greater disparities, unsurprisingly, lead to more pronounced negative side effects. Notably, individuals with leg length discrepancy are likely to limp proportionate to the length disparity. Gait truncation and asymmetry are also to be expected.
The more dramatic the length difference, the more likely the condition is to affect both sides of the body. For example, a difference of 3/8” increases the risk of knee pain and osteoarthritis in the shorter leg. However, a disparity twice that, 3/4”, leads to pain and arthritis in both knees. The legs are affected differently in other ways. The longer limb is 73% more likely to incur stress fractures, and the side with the longer leg is more likely to develop arthritis of the hip requiring total hip replacement.
Patients can experience pain anywhere from the low back to the feet, especially through the pelvis and hips. Disorders in postural movement coordination can also result. Scoliosis and other significant changes in spinal posture are common, and because the pelvis is consistently not level, reduction of postural stability is expected. The pelvis and sacrum tilt toward the shorter leg, and this improper loading of weight distribution causes the femoral head to deteriorate abnormally quickly.
Correcting the Issue
Once the exact measure of the disparity is determined and noted, adjustments, muscle work, and lifestyle changes can be assigned to correct the problem. The extent and regularity of treatment depends on the severity of the leg length discrepancy, but the result is usually retrained muscles and better balance.
Treatments are most effective in children younger than 15 years of age. Their still-developing bodies respond well to consistent treatment methods and regular monitoring (approximately every 3-6 months). Superficially, minor adjustments can be made by adding a small lift to one shoe. This change does not alter the length of the leg but it can relieve some of the pressure on the spine, hips, pelvis, and knees.
In cases of severe leg length discrepancy, corrective surgery is also a possibility. However, most patients see success with less-invasive means that include physical therapy and medical adjustment.