1. Neurosurgical Center Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
2. Department of Neurosurgery, Slotervaart Hospital, Amsterdam, The Netherlands.
3. Department of Neurosurgery, HagaZiekenhuis, The Hague, The Netherlands.
4. Department of Neurosurgery, Leiden University Medical Center, Leiden, The Netherlands.
5. Department of Orthopedic Surgery, University Medical Center Utrecht, Utrecht, The Netherlands.
6. Neurosurgical Center Amsterdam, Academic Medical Center, Amsterdam, The Netherlands.