Unilateral traumatic necrosis of the femoral head does not usually develop bilaterally; unilateral non-traumatic necrosis of the femoral head may develop bilaterally, but there is no definite time. The causes of femoral head necrosis are divided into two main categories: traumatic femoral head necrosis, i.e., necrosis of the femoral head caused by fracture or hip dislocation, usually involves one side and does not develop bilaterally. Non-traumatic necrosis of the femoral head, on the other hand, is caused by the use of corticosteroid drugs and alcohol abuse, which leads to blood vessel blockage and may develop into bilateral necrosis of the femoral head. Traumatic necrosis of the femoral head may result in unilateral necrosis of the femoral head on the affected side because the injury blocks the blood flow around the femoral head, but the blood flow on the healthy side is not blocked and does not lead to necrosis. Non-traumatic necrosis of the femoral head, if the unilateral necrosis of the femoral head, that is, has affected the blood vessels around the femoral head, destroying the blood flow of the femoral head, may also develop into bilateral necrosis of the femoral head, but the specific time, can not be clarified. Necrosis of the femoral head should follow the doctor’s instructions for standardized treatment in a timely manner, and should not be treated on its own, so as not to delay the condition.