LLD is a condition where the two legs are noticeably different in length. While a subtle difference of just a few millimeters is common and often causes no symptoms, a more significant variation can disrupt the body’s biomechanics. The body unconsciously attempts to compensate for this imbalance, which can lead to a cascade of issues over time. This compensation affects how a person walks and stands, ultimately placing undue stress on the musculoskeletal system.
Structural vs. Functional Discrepancies
Leg length discrepancies are categorized into two primary types based on their underlying cause: structural and functional. A structural, or true, LLD involves an actual difference in the bone length, typically within the femur or the tibia. Structural LLD can be congenital, or acquired later in life due to events like a severe fracture, damage to a growth plate in childhood, or bone infection.
A functional LLD occurs when the legs are physically the same length, but a problem elsewhere in the body creates the appearance of a discrepancy. This difference is often caused by mechanical issues like a pelvic tilt, muscle contractures, or a spinal curvature such as scoliosis. Functional LLD causes one leg to function as if it were shorter or longer than the other due to alignment issues.
The distinction between these two types dictates the appropriate treatment path. Applying a shoe lift to a structural LLD helps equalize the leg lengths, but using a lift for a functional LLD without addressing the underlying muscular issue may worsen the problem. Functional discrepancies are typically addressed through targeted physical therapy and exercises to correct muscle imbalances and joint mobility.
How Leg Length Discrepancy Affects the Body
The body attempts to counteract the unevenness of LLD through a series of compensations, which can ultimately lead to pain and injury. One common effect is an altered gait, or limp, as the person tries to keep their head level and their stride even. To compensate, an individual may walk on the ball or toes of the shorter leg, or they may excessively bend the knee of the longer leg to clear the ground.
These compensatory movements place uneven load and strain on the joints, resulting in chronic pain. The most frequent site of discomfort is the lower back, where the body’s attempt to level the pelvis causes rotation and tilt of the lumbar spine, sometimes resulting in a functional scoliosis. Hip and knee pain can also develop due to the asymmetrical wear and tear placed on the joint cartilage.
Over time, this uneven loading affects the entire kinetic chain, potentially causing muscle imbalances, joint stiffness, and even foot deformities. The hip on the shorter side may be positioned higher, and the shoulder on the longer side may drop lower, further altering the body’s symmetry. This chronic misalignment can increase the risk of developing degenerative conditions like arthritis in the overloaded joints.
Accurate Diagnosis and Measurement
Accurate diagnosis of LLD relies on a combination of a thorough physical examination and precise medical imaging. The initial assessment involves observing the patient’s standing posture and gait, often using wooden blocks to visually estimate the discrepancy needed to level the pelvis. Simple tape measure measurements are used as a screening tool, but these methods lack the precision required for treatment planning.
The gold standard for quantifying a structural LLD is specialized imaging, typically a full-length standing X-ray known as a scanogram or a CT scanogram. These images capture the entire length of the legs, from the hips to the ankles, allowing for accurate measurement of the actual bone lengths. The CT scanogram is often considered the most accurate, as it minimizes positioning errors that can skew the results.
Treatment decisions are based on the exact magnitude of the difference, measured in centimeters. For functional LLD, diagnosis focuses on assessing muscle flexibility, joint mobility, and pelvic alignment. Imaging is used primarily to rule out a true structural difference before focusing on a physical therapy approach.
Treatment Based on Severity
Treatment for LLD is carefully tailored to the severity of the discrepancy and whether the cause is structural or functional. For minor structural differences, generally defined as less than two centimeters, conservative management is the standard approach. This typically involves using a shoe lift, either placed inside the shoe or built into the sole, to effectively equalize the leg lengths.
Physical therapy is a common initial step for all patients and is the primary treatment for functional LLD, focusing on strengthening weak muscles and restoring proper pelvic and spinal alignment. For structural LLDs between two and five centimeters, shoe lifts and orthotics are common, but patients may also be candidates for surgical intervention if conservative methods do not resolve pain.
For moderate to severe structural discrepancies, typically exceeding two to five centimeters, surgical options are considered. In growing children, a procedure called epiphysiodesis may be performed to slow the growth plate in the longer leg, allowing the shorter leg to catch up over time. For skeletally mature patients, surgical lengthening of the shorter limb or shortening of the longer limb may be necessary to achieve equalization.