1. Department of Orthopaedics , Leiden University Medical Center , Leiden , The Netherlands
2. Department of Epidemiology and Biostatistics and the EMGO Institute for Health and Care Research , VU University Medical Centre , Amsterdam , The Netherlands
3. Department of Orthopaedics , Alrijne Ziekenhuis , Leiderdorp , The Netherlands
4. Department of Health Sciences and the EMGO Institute for Health and Care Research , VU University , Amsterdam , The Netherlands