The muscles that make the hip joint internally adducted and internally rotated are divided into two groups, the adductor group and the internal rotator group, and do not act as separate muscles. 1. Adductor group: pubococcygeus muscle, thin femoral muscle, long adductor, short adductor, large adductor. At the same time, these muscles also have the function of making the hip joint rotate outward. 2. Internal rotator muscles: semitendinosus, semimembranosus and suture muscles can rotate the hip joint inward when it is already flexed. The anterior portion of the gluteus medius and gluteus minimus muscles, in addition to rotating the hip inward, also abducts and rotates the hip outward (posterior portion of the muscle group). The hip joint consists of the acetabulum and the head of the femur, which is surrounded by several ligaments (iliopsoas ligament, femoral head ligament, etc.). This structure allows the hip joint to have a much lesser range of motion than the shoulder joint, but with greater stability, making it adaptable to weight-bearing and walking functions. The posterior inferior portion of the hip joint capsule is relatively weak, and sometimes the femoral head can dislocate posteriorly and inferiorly.