It is possible for the long and short legs to become heavier and heavier. There are several mechanisms or reasons for this situation: First, it may be caused by a greater load on the short side. This kind of patients as long as the ground weight-bearing activities, may cause the short side of the leg has a greater external load. Over time, this side of the lower limb wear and tear relative to the opposite side of the heavier, then will produce osteoarthritis or osteonecrosis, which will lead to this side of the lower limb becomes shorter. Second, this condition may be caused by lesions related to the spine and pelvis. Once the patient has unequal length of both lower limbs, abnormal gait will be produced during walking. At this time, in order to maintain balance, the patient will make the spine pelvis overactive, and over time, it will cause it to have excessive tilt, and then make the situation of long and short legs more serious. Third, this situation may be caused by the aggravation of the primary disease that causes such symptoms. For example, some patients have congenital hip dislocation, or scoliosis, or ischemic necrosis of the femoral head. These diseases will be aggravated gradually during the patient’s weight-bearing activities on the ground. Once these diseases are aggravated, the inequality of both lower extremities will also be aggravated.