Limb length discrepancy is a difference between the lengths of the arms or legs. Except in extreme cases, differences in arm length do not usually impact how the arms function and do not require treatment. A discrepancy in leg length will usually become obvious to parents as they watch their child grow and begin to crawl and walk. Some children are born with legs of different lengths (congenital reason). In other cases, injury to the growth plate or its illness due to infection or tumor for example causes a discrepancy in length to develop over time (developmental), and may be even combined with limb angular deformity. While a slight difference in leg length may not cause symptoms, a significant difference can cause a noticeable limp and make it difficult for a child to run and play. Treatment for a discrepancy depends upon the severity. In many cases, a minor difference in leg length can be evened out by wearing a lift in one shoe. A child with a more significant difference, however, may benefit from surgery to make his or her legs the same length. This can be done a number of ways, either shortening of the longer limb, or lengthening of the shorter limb, or both in extreme cases. Lengthening can be performed either externally or internally. The lengthening process begins approximately 5 to 10 days after surgery with a rate approximately 1 mm per day. When the bones are gradually pulled apart (distracted), new bone will grow in the space created. Muscles, skin and other soft tissues will adapt as the limb slowly lengthens.