1. Department of Orthopaedic Surgery, University Hospital Groningen, the Netherlands
2. Biomechanics Section, Mechanical Engineering Department, Imperial College, London, United Kingdom
3. Orthopaedic Department, University Hospital Nijmegen, the Netherlands
4. Biostatistical Department, University Hospital Nijmegen, the Netherland
5. Musculoskeletal Surgery Department, Imperial College, London, United Kingdom