A leg imbalance, formally known as Leg Length Discrepancy (LLD), occurs when the two lower limbs are of unequal length. Even minor differences alter the body’s mechanics, leading to changes in gait, posture, and pain in the back, hips, knees, and ankles. This asymmetry forces the body to compensate, often resulting in a limp or an uneven distribution of weight that strains joints and soft tissues. Addressing LLD requires an accurate diagnosis of the underlying cause and precise measurement of the difference to determine the most effective correction strategy.
Understanding the Types of Leg Length Discrepancy
Leg length discrepancies are categorized into two primary types: structural and functional. The structural, or anatomical, LLD represents an actual difference in the length of the bones in the leg, typically involving the femur (thighbone) or the tibia (shinbone). This type of imbalance is directly measured from one bony point to another and reflects a true skeletal asymmetry.
Functional LLD, also referred to as apparent or compensatory, exists even when the leg bones are of equal length. This perceived difference is caused by issues originating higher up the kinetic chain, such as a pelvic tilt, muscle contractures, or a scoliosis in the spine. For example, a tight hip flexor or an over-pronated foot can cause one leg to appear shorter than the other by altering the alignment of the pelvis and hip joint.
The treatment approach for a leg imbalance hinges on which type is present, making this differentiation fundamental to successful treatment. Correcting a functional discrepancy with a shoe lift, which is appropriate for a structural LLD, would not address the underlying muscular or joint issue.
Identifying the Cause and Measuring Severity
Identifying the cause of a leg imbalance involves assessing the patient’s history, as LLD can arise from various origins. Congenital conditions, where the difference is present from birth, and developmental disorders that affect growth plates are common causes, particularly in children. Trauma, such as a severe fracture that heals in a shortened position or an injury to a growth plate, is another source of structural LLD.
Physicians use specific diagnostic methods to confirm the presence of a structural LLD and to measure its severity precisely. A physical examination may involve the use of calibrated blocks placed under the shorter limb until the pelvis appears level, providing an estimate of the difference. Imaging techniques are then employed to confirm this measurement and pinpoint the location of the discrepancy.
The gold standard for measurement often involves a full-length standing X-ray, known as a scanogram or orthoroentgenogram, which captures the entire lower limb on a single image with a ruler for accuracy. CT scanograms are also used, offering highly accurate measurements. Severity thresholds generally dictate the course of action: discrepancies under 2 centimeters are typically managed conservatively, while larger differences often require surgical intervention for equalization.
Conservative Management Options
For individuals with mild structural imbalances or functional discrepancies, non-invasive treatments offer effective ways to restore symmetry and reduce associated strain.
The most common solution for a structural LLD is the use of shoe lifts or heel lifts, which are modifications designed to equalize the leg length. These can be internal lifts placed inside the shoe or external modifications added to the sole of the shoe for greater height correction. Shoe lifts are typically appropriate for structural differences up to about 2 centimeters, as adding more height internally can cause the foot to slip out of the shoe.
When the discrepancy is greater than 2 centimeters, external sole modifications can be applied to the shoe itself, allowing for a correction of up to 5 centimeters in some cases. The goal is not always full correction initially, as the body may need time to adapt to the change in alignment.
Functional imbalances are best addressed through targeted interventions like physical therapy and exercise. A physical therapist can identify muscle weaknesses, tightness, or pelvic rotation contributing to the apparent difference. Treatment focuses on strengthening the core and hip abductor muscles, such as the glutes, and stretching contracted muscles like the hip flexors, which can pull the pelvis out of alignment.
Orthotics and insoles are specific devices used to address functional LLDs related to foot mechanics, such as excessive pronation or arch collapse. By supporting the arch and correcting the foot’s position, a custom orthotic can prevent the chain reaction of misalignment that travels up to the knee and hip. Manual therapies, including chiropractic or osteopathic treatment, can also be utilized to correct joint restrictions or pelvic misalignments.
Surgical Treatments for Large Discrepancies
When a leg imbalance exceeds 2 to 3 centimeters, or when conservative measures fail to provide adequate relief, surgical options become necessary to physically equalize the limb lengths. These procedures are reserved for patients with significant structural LLDs.
One approach is limb lengthening, a method employed to slowly grow the shorter bone. This process, known as distraction osteogenesis, involves surgically cutting the bone (osteotomy) and then applying an external or internal device that gradually pulls the two bone segments apart. The body responds by generating new bone tissue in the gap, a slow process that can take several months to achieve the desired length. Newer internal lengthening nails, which are magnetically or electrically controlled, have made this procedure less cumbersome than traditional external fixators.
Alternatively, a limb shortening procedure may be considered on the longer leg for skeletally mature patients or in children where growth is still occurring. In children, a technique called epiphysiodesis is performed, where the growth plate of the longer leg is temporarily or permanently slowed or stopped. This allows the shorter leg to catch up as the child continues to grow. For adults, bone resection involves removing a segment of the longer bone, typically the femur or tibia, and then stabilizing the remaining bone with plates, screws, or an internal rod.