The femur and tibia growth happens around the so-called growth plates. Growth plates are cartilage areas located between the trumpet-shaped part of the shaft of the bone (the metaphysis) and the rounded end (the epiphysis).
A break in a child’s bone right at the growth plate, for example, can cause permanent damage, which may slow or stop the growth in that area altogether. Hence, the other leg may grow faster than its counterpart, and a difference in length will develop over time.
Conditions that may affect the growth plates are congenital diseases (present at birth) or acquired conditions, including trauma, broken bones, degenerative bone disorders, or joint replacement surgery (total hip arthroplasty).
Conversely, a broken bone in a child that does not involve the growth plate could cause it to grow faster for several years after healing. Hence, the affected limb will become longer than the bone on the opposite side of the body.
Also, bone infections such as osteomyelitis, juvenile arthritis, bone tumors, and bone cysts in growing children can cause a significant limb length discrepancy. Moreover, cerebral palsy, polio, and other neuromuscular disorders can cause problems with a child’s hip alignment and overall posture. This is known as functional limb-length discrepancy.
Even though the leg bones are equal in length, it may seem like one leg is longer than the other.