There are four main reasons for the difference in thickness between the legs: first, congenital dysplasia on one side of the leg, manifesting as one side of the limb and muscle development than the other side to unsound, there will be a thick leg and a thin leg. The second, due to nerve damage, resulting in one side of the lower limb without innervation or hyperalgesia, will lead to muscle contraction and diastole function decline, after a long time there will be a decline in function of muscle atrophy, and leg thinning. The third, due to fractures or trauma resulting in muscle and surrounding tissue damage for external fixation, which will lead to muscle at rest, not able to contract and diastolic activities, over time will also lead to muscle atrophy, the situation of thin legs. The fourth, due to some work or life in general, like to favor one side of the limb force, will lead to one side of the lower limb to get obvious exercise, muscle strength will be more increased, and muscle also become more full, so it will be thicker than the other side of the lower limb to appear some.