This study mainly measures the orientation of acetabulum cup post total hip arthroplasty. Using "Liaw's Version", a new and accurate standardization method, investigators are trying to analyze acetabulum cup anterversion change postoperatively.

Patients undergoing total hip arthroplasty have generally good prognosis. However, clinically there was still a minority of patients who suffered from persistent postoperative pain. Dislocations of hip leading to revision surgeries were as well observed in some patients.

This study mainly measures the orientation of acetabulum cup post total hip arthroplasty. Using "Liaw's Version", a new and accurate standardization method, investigators are trying to analyze acetabulum cup anterversion change postoperatively.

As previously known, the anteversion of acetabulum cup determines the range of motion, stability, and the function after total hip arthroplasty. Cup malalignment increase impingement, dislocation, cup migration, and polyethylene wear. Finding a pattern may help the early diagnosis of acetabular loosening.

Inclusion Criteria:

• Patients undergone total hip arthroplasty
• Patients undergone total hip arthroplasty with more than two postoperative X-ray plain films

Exclusion Criteria:

• Patients with postoperative periprosthetic fracture(s)
• Patients with postoperative infection
• Patients undergone revision total hip arthroplasty

Patients of hospital