1. Division of Neurosurgery
2. Belfast City Hospital, Lisburn Road, Belfast BT9 7AB, Northern Ireland.
3. 2114 Rose Creek Boulevard, Fargo, North Dakota, USA.
4. Division of Orthopaedic Surgery, Sunnybrook and Women’s College Health Sciences Centre and the University of Toronto, Room MG 361, 2075 Bayview Avenue, Toronto, Ontario, Canada M4N 3M5.