Leg length discrepancy (LLD) is a condition where one lower limb is measurably shorter than the other. This difference can be minor, with many people having a slight, asymptomatic variation, or it can be significant enough to affect walking, posture, and joint health. The difference in length can occur in the thigh bone (femur) or the shin bones (tibia or fibula). Seeking correction involves determining the exact cause and degree of the difference to choose the most appropriate treatment pathway.
Understanding the Underlying Causes
LLD causes fall into two categories: congenital and acquired. Developmental or congenital conditions arise when the limb does not form or grow properly during gestation, leading to a structural difference in bone length. Examples include fibular hemimelia, where the fibula is partially or completely missing, or proximal focal femoral deficiency, which results in a shortened or malformed femur.
Acquired LLD results from an event or condition that affects normal bone growth or causes bone loss after birth. A common cause is trauma, particularly a severe fracture that heals in a shortened position or damages the growth plate in a child. Infections in the bone, such as osteomyelitis, can also disturb the growth center, leading to a permanent growth arrest in the affected limb. Previous surgical procedures, such as total hip arthroplasty, may also result in a noticeable difference in leg length.
Accurate Measurement and Diagnosis
Initial clinical examination often involves “block testing,” where calibrated wooden blocks are placed under the shorter foot while the patient stands to level the pelvis. This provides a preliminary estimate of the required compensation but is not definitive for structural length.
For an accurate assessment of the true anatomical difference, specialized imaging techniques are required. The gold standard is a full-length standing radiograph, known as a scanogram, which captures the entire lower extremity on a single image. This method allows for precise measurement from the hip to the ankle using calibrated markers. CT scanograms are also utilized, offering highly accurate bone length measurements with relatively low radiation exposure.
Non-Surgical Management Strategies
Discrepancies generally less than 2 centimeters are most commonly managed using compensation methods. The most straightforward intervention is the use of a shoe lift or heel lift placed inside the shoe of the shorter leg.
Internal shoe lifts are generally limited to a height of about 10 millimeters (3/8 of an inch), as anything taller can cause the heel to slip out or make the shoe unstable. For discrepancies requiring greater height, an external shoe modification is necessary, where material is added directly to the sole of the shoe. These external lifts can accommodate differences up to 5 or 6 centimeters.
Custom orthotics may also be prescribed to address resulting foot pronation or alignment issues, providing stability in addition to the lift. Physical therapy supports management by focusing on stretching and strengthening muscles that may have tightened or weakened due to the body’s compensatory mechanisms. In children, non-surgical management is coupled with careful, periodic monitoring to project the final discrepancy at skeletal maturity.
Surgical Correction Procedures
Surgical intervention is typically reserved for LLDs exceeding 2 to 3 centimeters or when non-surgical methods fail to alleviate pain or functional limitations. The surgical strategy depends heavily on the patient’s age and whether their growth plates are still active. These procedures focus on either shortening the longer leg or lengthening the shorter leg.
Epiphysiodesis (Growth Arrest)
This technique is performed on children with active growth plates to slow the growth of the longer leg. The surgeon performs a minimally invasive procedure to temporarily or permanently halt the function of the growth plate (physis). This is often achieved by placing small metal plates and screws across the growth plate to tether it. Precise timing is essential, calculated based on remaining growth potential to achieve the closest possible limb length equality before the child reaches full skeletal maturity.
Shortening Procedures
The longer leg can be shortened through an osteotomy once the patient has reached skeletal maturity. In this surgery, a segment of the bone (either the femur or the tibia) is surgically removed. The remaining bone ends are then fixed internally with a metal rod or plates and screws to allow for healing. The femur can typically be shortened by up to 5 centimeters, while the tibia is generally limited to around 3 centimeters, to minimize the impact on surrounding soft tissues.
Lengthening Procedures
Limb lengthening increases the length of the shorter limb. The procedure begins with an osteotomy, where the bone is cut into two segments. A device, such as an external fixator (e.g., Ilizarov frame) or an internal lengthening nail, is then applied. The lengthening process, known as distraction osteogenesis, begins a few days after surgery, gradually pulling the bone segments apart by about 1 millimeter per day. This slow separation stimulates the body to regenerate new bone in the gap until the desired length is achieved, typically adding about one inch of length per month.