What causes limb length discrepancy?

A true discrepancy means the bones of one leg measure differently. This may arise during growth, after an injury that affects a growth plate, or after a fracture heals in a changed position. Hip, knee, or ankle surgery can also alter measured limb length. A growth plate fracture is a common cause when an injury disrupts normal bone growth in a child or teenager.

An apparent discrepancy occurs when the bones are similar in length but the pelvis, hip, knee, or foot position makes one side functionally shorter. Muscle tightness, a fixed joint position, or spinal and pelvic alignment can contribute. A visual impression alone cannot distinguish these mechanisms.

A clinician compares standing posture, walking pattern, joint movement, and leg lengths. Measurements may be repeated with blocks under the shorter-appearing side, and imaging can be considered when a structural difference needs confirmation. Treatment depends on the cause and how much it affects comfort, movement, or growth. Options may include observation, physiotherapy, a shoe lift, or specialist treatment.

Arrange an assessment for a new or worsening difference, persistent limp, hip or back discomfort, or a change after a fracture or operation. Children should be reviewed if one leg appears shorter, growth seems uneven, or walking changes. Seek prompt care after a new injury with severe pain or inability to bear weight.

Ask whether the difference appears structural or functional, how it was measured, whether growth remains affected, and whether a lift or physiotherapy could help. Discuss how often it should be monitored and which changes would warrant reassessment.