The most common causes of dislocation after artificial total hip arthroplasty include incorrect anterior tilt angles of the acetabular and femoral prostheses, impingement, and low soft tissue tone. One of the most common causes is incorrect anterior tilt of the prosthesis. Is the anteversion angle of the acetabular prosthesis a constant value in total hip arthroplasty? For example, 15°, 20° or 25° of anterior tilt? The answer is no. You have to adjust the anterior tilt of the acetabular prosthesis during surgery according to the anterior tilt of the femoral prosthesis, which may be 0° or 30° and is not a constant value. If you fit the acetabular prosthesis at a constant angle, for example 15°, you will be fine in most cases, but this angle is not appropriate for some patients and may lead to dislocation. Unfortunately, many orthopaedic surgeons are not aware of this. That is why the concept of joint anterior tilt angle and lateral femoral priority is introduced here. Ranawat, Jolles, Widmer, Dorr et al. found that the range of activities of daily life can be met as long as the sum of the anteversion angles of the acetabular cup prosthesis and the femoral prosthesis, i.e., the joint anteversion angle, is within a certain range, but they proposed different values for the joint anteversion angle.Dorr’s criteria for the safety zone of the joint anteversion angle are widely accepted by clinicians: 25° to 50°, or 37°±12°, slightly greater in women and slightly less in men. The safety zone for the joint anteversion angle does not reflect the patient’s anatomy and may not be consistent with the patient’s anatomy. Anatomical data show a large variability in the anterior tilt angle of the femoral neck, ranging from 10° posterior to 30° anterior. In non-cemented THA surgery, the epiphysis-filled femoral stalk cannot rotate within the medullary cavity, and the shape of the femoral neck osteotomy, the physiological curvature of the femoral stem, and the isthmus in the intertrochanteric region of the femur determine the anteversion angle of the femoral prosthesis, so the anteversion of the femoral prosthesis is often difficult to control. In addition, the anteversion angle of the femoral prosthesis is not necessarily the same as the anatomical anteversion angle of the femur, with some reports suggesting a difference of more than 10°. Since the anteversion angle of the femoral prosthesis is not constant and difficult to adjust, whereas the angle of the acetabular cup prosthesis can be easily adjusted (hemispherical after acetabular grinding and filing), some scholars have proposed the concept of femur first (stem first or femur first). During surgery, the anterior inclination of the femoral trial (medullary file) is determined first, and then the anterior inclination of the acetabular cup trial is adjusted so that the anterior inclination of the acetabular cup trial = (joint anterior inclination – anterior inclination of the femoral trial).