The answer to whether one leg can be shorter than the other is yes, a condition known as Leg Length Discrepancy (LLD) or anisomelia. Many people have a slight difference, often under 5 millimeters, which is usually asymptomatic and considered a normal human variation. When the difference is greater, it can alter the body’s posture and movement patterns, potentially leading to pain and musculoskeletal issues over time. Understanding LLD requires distinguishing between its two fundamental types, which determines diagnosis and management.
Understanding Structural Versus Functional Discrepancy
LLD is categorized into two types: structural and functional. A structural, or anatomical, discrepancy occurs when there is an actual physical difference in the length of the bones in the lower limb, specifically the femur or the tibia. This means the skeletal components themselves are unequal, making one leg inherently shorter or longer.
A functional, or apparent, discrepancy occurs when the bones of both legs are equal in length. The perceived difference is caused by an imbalance or misalignment elsewhere in the body, which pulls the lower limb out of symmetry. Common sources include muscle contractures, severe foot pronation, or a tilt or rotation of the pelvis or spine. The legs are the same size, but the body’s posture makes one appear shorter.
Common Causes of Unequal Leg Lengths
Structural LLD often stems from factors affecting bone growth during childhood. Congenital conditions, such as fibular hemimelia or proximal focal femoral deficiency, result in an underdeveloped limb at birth. Acquired causes are more common and typically involve a traumatic event, such as a severe fracture that damages the growth plate (physis) in a young person.
Other acquired causes include bone infections like osteomyelitis, bone tumors, or conditions leading to excessive growth in one limb. In adults, a structural difference may occur following hip or knee replacement surgery if the components are not precisely matched. Functional LLD is typically a product of soft tissue and joint mechanics.
This apparent shortening can result from chronic muscle tightness in the hip flexors or hip rotators, causing the pelvis to hike up on one side. Foot issues, such as excessive pronation or supination, can also alter the height of the leg relative to the ground. Postural habits and joint problems, particularly in the hip or sacroiliac joint, contribute to the misalignment.
How Leg Length Discrepancy Affects the Body
The human body is an integrated kinetic chain, and a difference in leg length forces compensations that extend up the torso. The body attempts to keep the head level with the horizon, causing the pelvis to tilt downward on the side of the shorter leg. This pelvic obliquity initiates a compensatory curve in the spine, known as functional scoliosis, as the vertebrae shift to re-level the head.
This chain reaction places uneven strain on the musculoskeletal system, leading to chronic pain. The longer leg typically experiences increased stress on the knee and hip joints due to altered loading patterns. Conversely, the shorter leg may experience increased tension in the ankle and foot, sometimes leading to plantar fasciitis or toe-walking. Biomechanical changes to gait, such as limping, can be detected with discrepancies as small as 5 to 10 millimeters.
Diagnosis and Treatment Options
Accurate diagnosis begins with a physical examination, including the use of measuring blocks placed under the shorter leg until the pelvis appears level. For a precise measurement of a structural difference, medical imaging like a scanogram or full-length standing X-ray (teleoroentgenogram) is required. These images measure the length of the bones directly.
Treatment is determined by the type, magnitude, and symptoms of the discrepancy. Functional LLD is primarily managed through conservative methods, including physical therapy, chiropractic adjustments, and custom orthotics to correct foot mechanics or muscle imbalances.
For structural LLD, differences less than 2 centimeters are often managed conservatively, usually with a shoe lift or heel insert. Discrepancies between 2 and 5 centimeters may require more involved intervention, such as surgical procedures. In skeletally immature patients, a procedure called epiphysiodesis may be performed to slow the growth of the longer leg, allowing the shorter leg to catch up. For differences greater than 6 centimeters, a limb lengthening procedure, which involves surgically cutting the bone and gradually distracting the segments, may be considered to achieve equalization.