1. Spine Unit, Department of Orthopedic Surgery; Rigshospitalet, University of Copenhagen; Copenhagen Denmark
2. Section for Transfusion Medicine; Rigshospitalet, Capitol Region Blood Bank; Copenhagen Denmark
3. Department of Anesthesiology, Center of Head and Orthopedics; Rigshospitalet, University of Copenhagen; Copenhagen Denmark
4. Division of Orthopedic Surgery; Texas Children's Hospital; Houston Texas