A difference in the length of the legs, known as Leg Length Discrepancy (LLD), is a common condition that can range from a few millimeters to several centimeters. This asymmetry is categorized into two main types: structural and functional. Structural LLD occurs when there is an actual difference in the bone lengths of the femur or tibia, often due to genetics, growth plate injuries, or previous surgeries. Functional LLD, which is far more common, arises when the bone lengths are equal, but muscle imbalances or joint issues—such as a rotated pelvis or fallen arch—make one leg appear shorter. Even minor discrepancies can disrupt the body’s natural alignment, forcing it into compensatory patterns that are the source of chronic pain.
How the Body Compensates for Uneven Lengths
The human body strives to keep the eyes and head level, initiating a chain reaction of mechanical adjustments throughout the skeleton. The most immediate and noticeable compensation is a pelvic tilt, where the pelvis drops down on the side of the shorter leg. This pelvic obliquity reduces the height difference but places the pelvis in an uneven position.
To maintain an upright posture above the uneven base, the spine develops a slight, sideways curve known as functional scoliosis. This temporary curve shifts the body’s weight away from the dropped pelvis and back toward the midline. This mechanical pattern introduces uneven stress on the spinal discs and facet joints, which can lead to discomfort in the lower back.
During walking (gait), the body employs further strategies to manage the asymmetry. The longer leg often compensates by flexing the knee and ankle more than normal, essentially shortening itself to clear the ground more easily. Conversely, the shorter leg may compensate by walking on the toes or increasing pronation in the foot to gain height. These unnatural movements place uneven strain on the joints and muscles of both legs, predisposing them to overuse injuries.
Understanding Pain Location on the Shorter and Longer Sides
The pain mechanism differs significantly between the two sides, meaning there is no single answer to which hip will hurt. The hip on the shorter leg side often experiences pain related to compression and increased load bearing. Because the pelvis drops and the leg constantly bears more weight to level the body, the hip joint is subjected to greater compressive forces.
This constant jamming can lead to joint degradation over time. Increased loading can also predispose the shorter limb to stress fractures or joint-related pain. Muscles on this side, like the hip flexors, may become chronically tight as they try to pull the leg up to meet the dropped pelvis. Pain on the longer leg side, however, is typically related to tension and overstretching.
The hip abductor muscles, such as the gluteus medius and the tensor fasciae latae, are continuously stretched and overworked as they fight to stabilize the elevated side of the pelvis. This chronic tension can result in inflammatory conditions like trochanteric bursitis or iliotibial band syndrome. Essentially, one hip hurts from being compressed, while the other hurts from being pulled taut.
The most frequent pain complaint related to LLD is not localized hip pain, but chronic lower back pain. This pain is a direct consequence of the compensatory spinal curvature the body creates to keep the head level. The uneven pressure on the lumbar spine’s discs and joints is a common source of persistent discomfort.
Accurate Measurement and Diagnosis Methods
Accurately quantifying the discrepancy is the first step in management. The simplest clinical assessment uses a tape measure to compare the distance from a fixed pelvic point (e.g., the Anterior Superior Iliac Spine) to the medial malleolus of the ankle. This direct measurement, while quick, is less reliable due to potential errors in landmark palpation and the inability to distinguish between structural and functional causes.
A more accurate clinical tool is the block test, where calibrated wooden blocks are placed under the shorter leg until the patient’s pelvis is level. The total height of the blocks then provides an estimate of the required correction. This method is valuable because it directly addresses the functional impact of the discrepancy on pelvic alignment.
For the most precise measurement, imaging techniques are the gold standard. A full-length standing X-ray (Scanogram or teleoroentgenogram) measures bone lengths down to the millimeter. This imaging is crucial for differentiating between true structural LLD and the apparent shortening caused by a functional issue like a pelvic rotation.
Non-Surgical Management and Correction
Non-surgical management is the primary approach for most LLD cases, especially those under two centimeters. The most common intervention for structural LLD is the use of shoe lifts or heel inserts placed in the shorter leg’s shoe. These lifts serve to physically equalize the leg length, thereby reducing the pelvic tilt and the resulting compensatory stress on the spine.
Clinicians often correct only 50 to 75 percent of the total measured discrepancy initially, allowing the body to gradually adjust to the new alignment. Lifts up to one centimeter can usually be placed inside the shoe; larger discrepancies require an external sole modification. Using a partial lift helps prevent the body from over-correcting and developing new compensatory problems.
Physical therapy plays a significant part in addressing functional LLD and muscular imbalances associated with structural LLD. Therapy focuses on strengthening weakened muscles, such as the hip abductors on the longer side, and stretching tight structures that may be contributing to an apparent shortening. Restoring core stability and symmetrical muscle function is necessary to maintain the benefits of any intervention.