Calvé-Legg-Perthes disease (CLP) is a hip disease in children whose femoral head becomes completely or partially necrotic. The disease is most common in five-six years of age. The femoral head is gradually deformed during the active stages of the disease (5-7 years). By healing, the hip joint shape will vary from an approximately normal joint to pronounced changes, the hip joint will be irregular. Such a hip joint is available for osteoarthritis. The purpose of this study is to map the function of the hip, the patient's quality of life and especially the risk factors that affect the outcome of the previous CLP. A nationwide prospective study of CLP was conducted between 1996 and 2000. All children with newly diagnosed Perthes disease (425) were registered. The current study will follow up all these patients with an average follow-up of 20 years. Radiological endpoints are evidence of hip osteoarthritis. Patient-reported outcomes (PROMS) should illuminate the function of the hip and quality of life.

Inclusion Criteria

- Subject was diagnosed with Perthes disease between 1996 and 2000 in Norway

Exclusion Criteria:

• Death upon follow up
• Other skeletal dysplasia
• Patient not able to give consent,

All patients which have been diagnosed with Perthes disease in between 1996 and 2000 in Norway were registered and follow at least 5 years after diagnosis. All hospitals throughout Norway with orthopaedic service were included in the registration. Our study is a 20 years follow-up of the original study.