1. HM Vermeulen, PT, MT, is Physical and Manual Therapist, Department of Physical Therapy, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, the Netherlands.
2. WR Obermann, MD, PhD, is Radiologist, Department of Radiology, Leiden University Medical Center
3. BJ Burger, MD, PhD, is Orthopaedic Surgeon, Medical Center Alkmaar, Alkmaar, the Netherlands
4. GJ Kok, PT, is Physical Therapist, Department of Physical Therapy, Leiden University Medical Center
5. PM Rozing, MD, PhD, is Professor of Orthopaedics, Department of Orthopaedic Surgery, Leiden University Medical Center
6. CHM van den Ende, PT, PhD, is Physical Therapist and Sociologist, Department of Physical Therapy, Leiden University Medical Center