1. Centre for Spinal Studies and Surgery, Nottingham University Hospital, Queens Medical Centre, Nottingham, United Kingdom;
2. Department of Orthopedic Surgery, Hospital for Special Surgery, New York, New York;
3. Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota; and
4. First Department of Orthopaedics, Athens University Medical School, Attikon University General Hospital, Chaidari, Greece