The failure to cock the leg is commonly caused by femoral head necrosis and acetabular labral injury, as follows: 1, femoral head necrosis: after ischemic necrosis of the femoral head on one side, the hip joint will have limited internal and external rotational and flexion activities, and therefore can not be cocked leg, and there will be severe pain symptoms, most of the patients will have persistent and severe pain, and the symptoms of pain are very obvious in their normal life, and the symptoms will be reduced after resting, 2, acetabular labral injury: in the process of strenuous exercise, acetabular labral injury can occur, the patient can not cock his leg. MRI will find that the femoral head has internal necrosis; 2. Acetabular labral injury: In the process of strenuous exercise, acetabular labral injury can occur, after the acetabular labral injury, the patient will show that the hip joint activity is limited, and it will be difficult to cross the legs, accompanied by severe pain symptoms, through the MRI to carefully observe, it can be found that the acetabular labral tearing site and the degree of injury, after the surgical treatment, it can gradually recover. Gradual recovery is possible.