Acetabular dysplasia often accompanies by acetabular bone hyperplasia and osteonecrosis of the femoral head. These pathological changes can alter the position of the center of the femoral head. Thus, measurement errors will be generated on the anteroposterior radiographs of the adult pelvis involving centre-edge angle, acetabular angle (Sharp angle), and acetabular head index, eventually resulting in the inaccurate diagnosis of acetabular dysplasia. Herein, the investigators describe the protocol to verify three novel X-ray indicators, including offshoring index (OFI), moving up index (MUI) and teardrop baseline offshoring index (TBOI) of the femoral head. All data will be expressed as relative ratios, as the investigators expect to make an accurate diagnosis through avoiding the generation of errors resulting from measurement angles.

Acetabular dysplasia is a developmental malformation of the hip joint where the acetabulum become shallow and cannot fully cover the femoral head and the centre of the hip joint moves outward, resulting in an increased risk for joint subluxation or dislocation.

Current diagnosis of acetabular dysplasia mainly depends on the pelvic anteroposterior X-ray film to understand whether there is dislocation of the hip joint, whether the concentricity of the femoral head and acetabulum is consistent, and whether there is secondary osteoarthritis or other hip diseases, such as femoral head ischemic necrosis, hip joint tuberculosis, and rheumatoid arthritis. The commonly used measurement indicators include centre-edge (CE) angle, acetabular angle (Sharp angle), and acetabular head index (AHI). Moreover, some differences exist in the measurement results between male and female patients. Acetabular dysplasia often accompanies by acetabular bone hyperplasia and necrosis of the femoral head, which have a greater impact on radiographic measurements, especially when measured with angles. It is difficult to determine the radiological landmark for the lateral edge of the acetabular roof due to the existence of bone hyperplasia, which produces a great influence on the accuracy of the measurement of the centre-edge angle and Sharp angle.

Inclusion Criteria:

• No experience in hip replacement, pelvic fixation or external fixation, and proximal femoral surgery;
• No marked pelvic tilt;
• No hip dislocation;
• No obvious hip deformity, such as significant collapse of the femoral head and severe hip traumatic arthritis;
• No significant lesions in the pelvis or proximal femur;
• Aged over 16 years;
• Provision of written informed consent.

Exclusion Criteria:

• Those with advanced osteoarthritis;
• Those with osteoarthritis secondary to acetabular dysplasia;
• Those with ankylosing spondylitis involving the hip joint;
• Those with rheumatoid arthritis;
• Those with inflammatory inflammation of the hip joint;
• Those with tumor lesions in the hip joint.

Potential patients will be informed of the study details through an announcement issued through the bulletin board of the Third Hospital of Hebei Medical University. Interested patients will directly contact the principle investigator via telephone, and among them, eligible patients will be required to provide written consent prior to the participation in the trial.