Leg length discrepancy (LLD), also known medically as anisomelia, is a common condition where one lower limb is shorter than the other. A large percentage of the population has a minor difference, often less than one centimeter, which typically causes no issues and goes unnoticed. When the difference is more significant, usually exceeding a centimeter, the body’s natural alignment and movement patterns can be negatively affected. Understanding the underlying cause is paramount because the correct treatment approach depends entirely on whether the disparity is rooted in the bone structure or an issue elsewhere in the body.
Understanding Structural Versus Functional Differences
The two types of leg length discrepancy are distinguished by where the physical difference originates. Structural LLD involves an anatomical difference in the length of the bones in the leg, specifically the femur or the tibia. This type of discrepancy is measurable via imaging like X-rays and represents a fixed difference in the skeletal structure. Treatment must physically address this fixed bone length difference.
Functional LLD means the bone lengths are equal, but one leg appears shorter due to an alignment issue higher up the kinetic chain. This apparent difference is often caused by a pelvic tilt, a muscle contracture, or a joint instability. A functional discrepancy is a positional problem, meaning the treatment focuses on correcting the soft tissue or joint mechanics causing the misalignment.
Primary Causes of Length Discrepancy
Structural leg length discrepancies stem from conditions that either shorten one leg or cause it to grow longer than the other. Causes can be broadly categorized into congenital, developmental, and acquired origins. Congenital conditions are those present at birth, often involving a failure of a bone, such as the fibula or tibia, to develop fully.
Developmental issues arise during childhood when the growth plates are still active. Conditions like Slipped Capital Femoral Epiphysis (SCFE) or infections of the bone (osteomyelitis) can damage the growth plate, causing one leg to stop growing prematurely or, in some cases, to grow at an accelerated rate.
Acquired discrepancies are the result of external events, with trauma being the most common trigger. A severe fracture, particularly one involving the growth plate in a child, may heal improperly and lead to a shortening of the bone. In adults, poorly healed fractures or bone removal during procedures like hip replacement surgery can also result in a measurable shortening of the limb.
How Discrepancy Affects Posture and Movement
A difference in leg length forces the body to create compensatory mechanisms to maintain balance and walk efficiently. This often begins with the pelvis, which tilts upward on the side of the longer leg to make up for the discrepancy, known as pelvic obliquity.
The tilting of the pelvis subsequently causes the lumbar spine to curve laterally, developing a functional scoliosis as the body attempts to keep the head centered over the hips. This uneven weight distribution places increased mechanical stress on the joints, ligaments, and muscles of the lower back, hip, and knee. Over time, these uneven forces can lead to chronic pain in the hip or lower back. The gait, or walking pattern, is also affected, often resulting in a limp, uneven stride length, and increased energy expenditure during movement.
Management and Treatment Options
Treatment for leg length discrepancy is based on the type and the measured difference in length. Non-surgical, conservative management is the first approach for smaller differences, especially those less than two centimeters. This often involves the use of shoe lifts or heel inserts, which are placed inside or attached to the shoe of the shorter leg to level the pelvis and correct the posture.
Physical therapy is another conservative option, especially for functional discrepancies, focusing on stretching tight muscles and strengthening weak ones to correct pelvic or spinal misalignment. For structural differences exceeding two centimeters, or for those causing significant symptoms, surgical intervention is considered.
One surgical approach for a growing child is epiphysiodesis, which involves stopping the growth plate of the longer leg to allow the shorter leg to catch up over time. For larger discrepancies in skeletally mature individuals, the two main surgical options are limb shortening or limb lengthening. Limb shortening involves removing a segment of bone from the longer leg, while limb lengthening uses specialized devices to slowly stretch and regenerate new bone in the shorter leg. The decision to pursue surgery weighs the severity of the discrepancy against the risks and recovery associated with the procedure.