1. Department of Health Sciences, Community and Occupational Medicine, University of Groningen, University Medical Centre Groningen, Groningen, Netherlands
2. Department of Orthopaedics, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
3. Department of Orthopaedics, Leiden University Medical Center, Leiden, Netherlands
4. Department of Epidemiology, Leiden University Medical Center, Leiden, Netherlands