1. Department of Trauma and Orthopaedic Surgery, Division of Orthopaedics, University Medical Centre Hamburg-Eppendorf, 20246 Hamburg, Germany
2. Department of Trauma and Orthopaedic Surgery, Division of Spine Surgery, University Medical Centre Hamburg-Eppendorf, 20246 Hamburg, Germany
3. Department of Joint Replacement, General and Rheumatic Orthopaedics, Orthopaedic Clinic Markgröningen, 71706 Markgröningen, Germany