A difference in the lengths of the two lower limbs, medically known as Leg Length Discrepancy (LLD), is a common orthopedic finding. Up to half of the population may have a subtle variation, typically less than one centimeter, that often goes unnoticed. LLD is generally classified into two types: structural and functional. A structural discrepancy represents an actual difference in the bone lengths of the femur or tibia. A functional discrepancy occurs when the bone lengths are equal but a muscular imbalance or pelvic tilt makes one leg appear shorter.
Identifying the Leg Length Difference
A person with LLD may first notice symptoms that appear unrelated to their legs, such as pain in the lower back, hip, or knee. This discomfort arises because the body attempts to compensate for the imbalance, causing uneven mechanical stress on the joints. Other signs of LLD include a noticeable limp, an uneven walking pattern, or a shoulder that appears lower on one side. A healthcare provider will conduct a physical examination, observing the patient’s posture and gait. A common screening method is the block test, which uses blocks placed under the shorter leg to estimate the discrepancy.
The gold standard for precise measurement is a full-length standing X-ray, sometimes called a scanogram. This specialized imaging captures the entire length of both legs on a single image, allowing doctors to measure the exact length of the femur and tibia in each limb. This evaluation is essential for accurately quantifying the structural discrepancy and guiding treatment decisions.
Understanding Why the Length Difference Occurs
LLD causes are broadly categorized based on when the condition develops. Congenital causes are present at birth, often resulting from one or more bones in the leg not developing fully during pregnancy. Examples include proximal focal femoral deficiency or hemihypertrophy, where one side of the body grows more than the other.
Developmental issues arise during childhood as the bones are growing, typically involving the growth plates (physes) near the ends of the long bones. An injury, infection, or radiation therapy affecting a growth plate can slow or stop the growth of that bone. This leads to a progressive shortening over time.
Acquired LLD results from trauma or disease occurring after skeletal maturity, or a fracture that heals improperly. A severe fracture of the femur or tibia may heal in a shortened position. Certain bone diseases or previous surgical procedures can also alter the bone length.
Managing Mild to Moderate Differences
For discrepancies less than two centimeters, conservative, non-surgical management is typically the first step and is often sufficient. Shoe lifts or heel lifts are the most common non-surgical intervention, designed to equalize the functional length of the legs. These lifts can be placed inside the shoe for smaller differences, or built into the sole of the shoe for larger ones. The goal is correction to a residual difference of one to two centimeters, which the body can often tolerate well.
Custom orthotics may be prescribed to address underlying foot mechanics or to help manage a functional LLD caused by pelvic or muscle imbalances. The orthotics support the foot and ankle, which helps stabilize the entire lower limb alignment.
Physical therapy plays an important role, particularly for managing the secondary effects of LLD, such as back or hip pain. Therapists focus on stretching and strengthening exercises to correct muscle imbalances that developed as the body compensated for the uneven legs. Specific stretches for the hamstrings, hip flexors, and piriformis muscles help reduce strain and improve overall movement patterns.
Options for Significant Discrepancies
When the leg length difference is greater than two centimeters, surgical intervention is generally considered to prevent long-term joint damage and functional limitations. The choice of procedure depends heavily on the patient’s age and whether they have finished growing. The two main surgical strategies are growth modulation and direct bone length adjustment.
For children and adolescents who still have open growth plates, the procedure known as epiphysiodesis is an option. This involves surgically slowing or stopping the growth of the longer leg to allow the shorter leg to catch up over time. The timing of this procedure is calculated based on the child’s remaining growth potential to achieve an equal length at skeletal maturity.
For skeletally mature individuals or those with very large discrepancies, the bone length itself must be altered. Limb lengthening involves cutting the shorter bone (osteotomy) and using a device, such as an external fixator or an internal magnetic nail, to gradually separate the bone segments. New bone tissue, called regenerate, slowly forms in the gap, a process that can take several months. Another option is limb shortening, where a segment of bone is removed from the longer leg.