1. Department of Orthopaedic Surgery, University of Colorado Denver, School of Medicine, Denver Health Medical Center, 777 Bannock Street, Denver, CO 80204, USA
2. Department of Trauma and Reconstructive Surgery, University Hospital Ulm, Steinhövelstraße 9, D-89075 Ulm, Germany
3. Department of Neurosurgery, University of Colorado Denver, School of Medicine, Denver Health Medical Center, 777 Bannock Street, Denver, CO 80204, USA