1. Center for Bionics and Pain Research, Mölndal, Sweden.
2. Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden.
3. Operational Area 3, Sahlgrenska University Hospital, Mölndal, Sweden.
4. Department of Orthopaedics, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.