1. Division of Orthopaedics; Danderyd Hospital and Department of Clinical Sciences; Danderyd Hospital; Karolinska Institutet; Stockholm Sweden
2. School of Education; Health and Social Studies; Dalarna University; Falun Sweden
3. Department of Women's and Children's Health; Karolinska Institutet; Stockholm Sweden
4. Center for Applied Biostatistics; Department of Medicine; Sahlgrenska Academy; University of Gothenburg; Gothenburg Sweden