Leg Length Discrepancy (LLD) refers to a difference in the lengths of a person’s lower limbs. This asymmetry forces the musculoskeletal system to compensate, placing uneven stress on the joints and soft tissues of the hip. Over time, this constant imbalance can lead to structural changes, muscle strain, and excessive wear, ultimately resulting in chronic hip pain.
Understanding Leg Length Discrepancy
Leg Length Discrepancy is categorized into two distinct types based on the underlying cause: structural and functional. A structural, or anatomical, LLD is a true difference in the length of the bones in the leg, such as the femur or tibia. This type of discrepancy can be present from birth due to congenital factors or acquired later in life from trauma, a poorly healed fracture, or as a result of certain surgeries like a total hip replacement.
A functional LLD, conversely, is an apparent difference in leg length where the bone measurements are actually equal. This apparent asymmetry is caused by issues higher up in the body, which pull the skeleton out of alignment, making one leg seem shorter or longer. Common causes of functional LLD include muscle tightness in the hip or low back, pelvic rotation, joint contractures, or scoliosis.
The type of LLD dictates the appropriate management strategy. Functional LLD is more responsive to physical therapy aimed at correcting muscular imbalances and restoring proper joint alignment. Structural LLD, which involves a fixed difference in bone length, typically requires an external solution to physically equalize the limbs. Differences of 10 millimeters (about 0.4 inches) or greater are more likely to cause symptoms, though discomfort can occur with smaller differences.
The Biomechanical Mechanism Causing Hip Pain
LLD leads to hip pain because the body attempts to maintain a level head and stable posture, introducing a chain of compensatory movements. The most immediate compensation is a lateral pelvic tilt, where the pelvis drops down on the side of the shorter leg. This tilt forces the spine to curve slightly to the side, which can stress the sacroiliac and lumbar joints.
This uneven foundation significantly alters how weight is distributed across the hip joints. The hip on the longer side is subjected to increased compression forces as it bears more weight. This excessive load can accelerate the wear of the articular cartilage, potentially leading to degenerative joint disease or labral irritation. Conversely, the hip on the shorter side may experience increased shear forces due to the altered joint angle.
The muscles surrounding the hip are subjected to chronic strain and imbalance. On the shorter side, muscles like the gluteal muscles and hip abductors are constantly stretched and work harder to lift the pelvis and prevent an excessive drop. This overworking can lead to fatigue, inflammation, and tendinitis in the hip and lateral thigh region. Simultaneously, muscles on the longer side, such as the hip flexors, may become chronically shortened or tightened, contributing to postural misalignment.
Clinical Assessment and Management
Accurately identifying and measuring LLD is the foundation for effective treatment, and the assessment process typically combines clinical examination and diagnostic imaging. Clinicians often perform a physical examination using techniques like block testing, where measured blocks are placed under the foot of the shorter leg until the pelvis appears level. This simple method provides an estimate of the required correction.
For a definitive measurement of the structural difference, imaging is necessary. Full-length standing X-rays, often called a scanogram or teleo-roentgenogram, are considered the most accurate method for measuring the true bony lengths. These images allow the healthcare provider to precisely measure the distance between specific bony landmarks, confirming whether the discrepancy is structural or merely functional.
Non-surgical management strategies are primarily aimed at equalizing the limb length or correcting the underlying biomechanical cause. For a diagnosed structural LLD, the most common treatment involves the use of heel lifts or full sole lifts placed inside the shoe of the shorter leg. This external support helps to level the pelvis, which reduces the compensatory stress on the hip joint and surrounding soft tissues.
Physical therapy is a cornerstone of management, particularly for functional LLD or for addressing the muscle imbalances that accompany structural LLD. Therapists utilize targeted exercises, stretches, and manual techniques to release tight muscles, such as the iliopsoas and quadratus lumborum, that may be hiking the pelvis. Strengthening exercises focus on the gluteal and core muscles to improve overall gait mechanics and restore proper joint stability, thereby easing the chronic strain contributing to hip pain.