In this study, the investigators retrospectively collected DDH case data of THA assisted by AI 3D planning and THA assisted by traditional planning. The compliance between preoperative planning and the type of prosthesis used in the operation, the position of the acetabular prosthesis, the correction of LLD and the postoperative joint function score were analysed to evaluate the short-term effect of AI combined with preoperative 3D planning in THA for DDH.

Inclusion Criteria:

• DDH was diagnosed by clinical signs and imaging examination, and a primary THA was planned;
• the patient had persistent unilateral hip pain, which seriously affected their quality of life;
• the standard posterolateral approach was used;
• the contralateral hip was normal or had received THA;
• the proximal femoral Dorr classification was type A or B;
• The acetabular classification was Crowe type Ⅰ, Ⅱ, Ⅲ or IV;
• all patients were treated with the bioartificial hip joint PINNACLE® cup or SUMMIT® stem, developed by Johnson & Johnson Biological.

Exclusion Criteria:

• preoperative and postoperative imaging examinations did not meet the evaluation criteria (non-standard double-hip anteroposterior film, acetabular angle and LL length could not be accurately measured);
• severe osteoporosis, tumour or metabolic disease around the affected hip joint;
• spinal deformity by other causes or a history of lumbar internal fixation;
• external deformity of the affected hip joint in the lower extremity;
• neuromuscular insufficiency (with hip abduction weakness and poliomyelitis);
• severe disease with intolerance to surgery.

Patients with DDH who underwent unilateral primary THA between January 2020 and July 2022 in the orthopaedic department.