The causes of hip joint external rotation snapping mainly include soft tissue adhesion contracture, trauma, iliotibial bundle hypertrophy and hip joint itself. 1. Adhesion contracture of soft tissues: the most common popping caused by the soft tissues on the outer side of the hip joint is mainly due to adhesion contracture of the gluteus maximus muscle, such as repeated injections in early childhood, which will cause contracture of the gluteus maximus muscle fascia, forming a scar as well as a striated structure, which will make these proliferated scar tissues slide in the greater trochanter when flexing and extending the thigh and cause the popping of the hip joint. 2. Trauma: due to trauma or strain injury, the soft tissue of hip joint can be congested, edema, aseptic inflammation, resulting in hypertrophy and fibrous tissue hyperplasia, i.e., scar tissue, if the symptom is very obvious, a cord-like, tough structure can be felt under the skin, which will be accompanied by snapping sound when flexing and extending the hip joint. 3. Hypertrophy of iliotibial bundle: some patients with hypertrophy of iliotibial bundle or hypertrophy of greater trochanter, there is bursitis, which can also lead to snapping sound when hip joint is externally rotated. 4. Hip joint itself: some diseases of hip joint itself such as chondroma of greater trochanter, or congenital dysplasia, hip dislocation and so on. Tear and damage of acetabular cartilage and labral injury can also cause hip snapping. Hip popping should be actively carried out physical examination, to be able to find out the cause of hip popping at an early stage, and take braking, immobilization, surgery and other ways to avoid the development of the disease.