1. Department of Surgery and Orthopaedics, University Hospital Maastricht, Maastricht, the Netherlands.
2. Faculty of Medicine, Department of Epidemiology, Maastricht University, Maastricht, the Netherlands.
3. Department of Rehabilitation Medicine, University Hospital Maastricht, Maastricht, the Netherlands.
4. Smeets & Zonen Orthopedische Schoentechniek, Geleen, the Netherlands.
5. Department of Internal Medicine, University Hospital Maastricht, Maastricht, the Netherlands.