Limb length discrepancy (LLD), also known as anisomelia, is a condition where one leg is shorter than the other. While minor differences are common and often unnoticeable, a significant discrepancy affects the body’s mechanics. This imbalance disrupts alignment, putting excessive stress on joints and the spine. This asymmetrical loading can contribute to an altered walking pattern or chronic pain in the lower back, hip, or knee.
Recognizing the Observable Signs
The first indication of LLD often comes from noticing subtle changes in posture and movement. A noticeable limp is a common sign, where the body compensates for the shorter leg, sometimes by walking on the tip-toes of that limb. Postural observations may reveal that one hip or shoulder appears consistently higher than the other when standing, as the pelvis tilts to level the body.
The body attempts to adapt to the length difference, which can manifest as chronic, unexplained pain in the lower back, hip, or knee. Examining footwear can also offer a clue, as the sole or heel of one shoe may show significantly more wear than the other due to uneven weight distribution.
Informal Home Assessment Techniques
If you suspect a difference in leg lengths, you can perform simple, non-diagnostic checks at home to gain an initial estimate. The standing block test involves placing thin, flat objects of known thickness, such as books, under the foot of the suspected shorter leg. You continue adding material until the hips and pelvis feel level, which can be checked by placing your hands on your hip bones. The total height of the stack provides a rough measure of the discrepancy.
Another method uses a flexible tape measure to compare leg lengths while lying flat on your back. Measure the distance from the anterior superior iliac spine (ASIS)—the bony prominence at the front of the hip—down to the medial malleolus (the inner ankle bone). It is helpful to have a partner perform this measurement to ensure accuracy and consistency. These home assessments are only approximations and cannot replace a professional medical evaluation, as they are susceptible to errors from soft tissue movement.
Clinical Diagnosis and Underlying Causes
A medical professional uses precise methods to definitively measure LLD, distinguishing between two primary types of discrepancy. Structural LLD represents a true anatomical difference in the length of the femur or tibia bones. Functional LLD occurs when the bones are equal in length, but alignment issues, such as a pelvic tilt from muscle tightness or scoliosis, create the appearance of a difference.
For a more accurate diagnosis, imaging is considered the gold standard. A full-length standing X-ray, sometimes called a Scanogram or teleoroentgenogram, is the preferred method. This technique captures the entire lower limb on a single film, allowing the orthopedist to measure bone lengths precisely. This imaging is crucial for calculating the exact structural difference and planning intervention.
The causes of LLD are broadly categorized as either congenital or acquired. Congenital LLD is present at birth, often due to developmental issues like fibular hemimelia (underdeveloped shin bone) or hemihypertrophy (one side of the body grows faster). Acquired LLD develops later in life, most commonly following a severe fracture in the leg bones, especially if the break affects a child’s growth plate or heals shortened in an adult. Other acquired causes include bone infections, tumors, or conditions like juvenile arthritis, which disrupt normal bone growth.
Treatment Options for Limb Length Discrepancy
Treatment for LLD is determined by the patient’s age, the cause, and the magnitude of the difference. For minor to moderate discrepancies, typically less than two centimeters, non-surgical intervention is the standard approach. This commonly involves shoe lifts or heel inserts placed inside or outside the shoe of the shorter leg to equalize the leg length.
For cases of functional LLD, physical therapy is often recommended to address underlying muscular imbalances, joint contractures, or postural issues causing the apparent length difference. If the discrepancy is significant, usually over two centimeters, surgical options may be considered by an orthopedic specialist.
Surgical Interventions
In growing children, a procedure called epiphysiodesis can be performed, which involves surgically slowing or stopping the growth plate of the longer leg to allow the shorter leg to catch up. For larger differences or in skeletally mature patients, limb lengthening procedures may be used. These involve cutting the shorter bone and gradually distracting the two segments over time to stimulate new bone formation. These interventions are reserved for severe cases where the benefits outweigh the risks.