Flat hip, also called Legg-Calvé-Perthes disease, is clinically characterized by flattened femoral head, shortened femoral neck, and a center of rotation of the femoral head lower than the apex of the greater trochanter. Joint replacement is difficult, with high intraoperative and postoperative complications. Especially, issues such as unequal limb length, postoperative dislocation, postoperative neurological damage, and prosthesis impact have always plagued clinical practice.

The robotic arm-assisted joint replacement technology has been developed and clinically applied for over 10 years, but it was not until the past 3 years that it began to be widely implemented worldwide. Existing research data indicates that robotic arm-assisted joint replacement technology can significantly improve the placement of prostheses and lower limb force lines in patients, and improve their short-term clinical prognosis. However, its application in complex hips, such as flat hip, is limited. More relevant literature is needed to further enrich people's understanding of this technology. In theory, robot assisted technology can solve many challenges faced in flat hip replacement.

Inclusion Criteria:

• patients with Legg-Calvé-Perthes disease and accept total hip replacement in our center

Exclusion Criteria:

• infection, cannot complete follow-up