1. Department of Orthopaedic Surgery, Zuyderland Medical Center, Heerlen, the Netherlands
2. Care and Public Health Research Institute (CAPHRI), Maastricht University, Maastricht, the Netherlands
3. Department of Neurosurgery, Maastricht University Medical Center, Maastricht, the Netherlands
4. Department of Neurosurgery, Zuyderland Medical Center, Heerlen, the Netherlands