1. Department of Physical Medicine, Rehabilitation and Occupational Medicine, Medical University of Vienna, General Hospital of Vienna, Vienna, Austria;
2. Otto Bock Healthcare Department of Research/Biomechanics, Göttingen, Germany;
3. Department of Orthopaedic Surgery, Medical University of Vienna, General Hospital of Vienna, Vienna, Austria;
4. Orthopaedic Rehabilitation Center Zicksee, St. Andrä am Zicksee, Austria