The common causes of femoral head necrosis in a 15-year-old boy include femoral head trauma, hip strain, and drug factors. 1. Trauma to the femoral head: If the femoral head of a 15-year-old boy suffers from serious trauma, such as crushing by vehicles, falling from a height and hitting by sticks, the weight-bearing trabeculae within the femoral head will be imperfectly repaired during the healing process, resulting in structural changes of the femoral head, which will lead to necrosis of the femoral head. 2. Hip joint strain: the femoral head is an important part of the hip joint, hip joint strain can affect the femoral head, if the hip joint strain affects the blood supply to the epiphysis of the femoral head, so that it is necrotic, and also in the developmental period of the 15-year-old boy, the femoral head has no place to develop, and it will be necrotic. 3. Drug factors: such as osteonecrosis caused by glucocorticoid drugs. If a 15-year-old boy needs to use a lot of glucocorticoid drugs for a long time, such as prednisone acetate tablets and hydrocortisone tablets, etc., it can lead to lipid metabolism disorders in the body, the formation of small thrombus, affecting the blood circulation of the femoral head, which leads to necrosis of the femoral head. Fifteen-year-old boys suffering from necrosis of the femoral head should pay attention to avoid overwork and strenuous exercise, protect the hip joint, go to the hospital in a timely manner, and standardize the treatment under the guidance of the doctor. Also control weight, so as not to aggravate the load-bearing burden of the femoral head.