Leg a thick a thin is a variety of diseases of the external manifestations, specific as follows: 1, leg fracture or muscle strain: due to the need to carry out the cast of the brake or long-term rest, the patient will appear in the affected leg muscle atrophy, so there will be a leg a thick and a thin. 2, congenital hip dislocation: dislocation of the side of the limb tends to use the frequency of use will be lower, the patient will be more than compensatory use of the healthy side of the limb, and therefore will also be 3, lumbar disc herniation: when the lumbar disc herniation compresses the sciatic nerve, it will cause unilateral radiating pain in the lower limbs, and the patient refuses to use the affected limb because of the pain, and mainly adopts the healthy side of the limb.