1. Department of Orthopaedics; University Medical Center Hamburg-Eppendorf; Martinistraße 52 Hamburg 20246 Germany
2. Department of Medical Biometry and Epidemiology; University Medical Center Hamburg-Eppendorf; Martinistraße 52 Hamburg 20246 Germany
3. Department of Osteology and Biomechanics; University Medical Center Hamburg-Eppendorf; Lottestr. 52 Hamburg 22529 Germany