Since the concept of “safe area” put forward by Lewinnek, it has been widely recognized. While in recent years, many scholars have found that even if the acetabular prosthesis was placed on the “safe area”, there were still many unexplained dislocation after total hip arthroplasty. And scholars began to question whether the “safe area” is really suitable for all patients. Spinal degeneration, deformity, lumbar fusion, etc. will lead to spine sagittal imbalance and changes in pelvic activity, which could lead to changes in acetabular orientation, and ultimately lead to edge loading, wear, impact, and even dislocation after total hip replacement. From the perspective of wear, impact and dislocation, it is determined by the functional positioning of the acetabular cup, not the anatomical positioning. The anatomical positioning and functional positioning of the neutral pelvic acetabular cup in the standing position can be considered equivalent. For pelvic rotation more than 20°, functional placement needs to be considered. In recent years, as the understanding of the internal relationship between the spine-pelvis-hip joint has become more and more profound, some scholars further classify the hip-spine relationship according to whether the spine is stiff or deformed, and propose corresponding acetabulums according to different types of hip-spine relationships The function of placement, so as to achieve a stable artificial hip joint. Therefore, it is of great significance to fully assess whether the patient’s sagittal plane is balanced before surgery to guide artificial hip replacement surgery.