O-legs, i.e. inversion of the knee, can be caused by calcium deficiency, heredity or poor sitting posture and other imbalance causes. Adults with knee diseases, such as osteoarthritis of the knee and knee tumors, can also cause inversion of the knee, but it has nothing to do with the legs. The main hazards of the legs are varicose veins in the lower limbs, knee joint diseases, pelvic tilt and so on. 1. Varicose veins of lower limbs: Erlang leg compresses the veins behind the knee, causing varicose veins of lower limbs and even thrombosis of lower limbs. 2. Knee joint disease: Erlang leg will affect the blood flow of the knee joint, so that the knee joint pressure increases, more likely to cause degenerative changes in the knee joint, arthritis, joint injuries and other knee joint diseases. 3. Pelvic tilt: Erlang legs can cause pelvic tilt, which may further cause scoliosis. Although the legs will not lead to O-legs, but there are other hazards, usually should pay attention to avoid. O-legs should go to the hospital in a timely manner, under the guidance of the doctor for treatment.