The joint between waist and hip is sacroiliac joint. Sacroiliac joint pain may be caused by muscle strain, trauma, lumbar disc herniation and so on. 1. Muscle strain: Sacroiliac joint pain is caused by prolonged exertion and lack of relaxation of the lumbar muscles. 2. Trauma: such as impact, fall can also lead to sacroiliac joint pain. 3. Herniated lumbar discs: Herniated lumbar discs can press on the sciatic nerve leading to pain, such as sacroiliac joint. There may be other causes of sacroiliac joint pain, such as sacroiliitis. If the symptoms do not improve after resting, it is recommended to go to the hospital in time to find out the cause of the disease and give the corresponding treatment and treatment.