1. Athens Naval Hospital, Ag. Sofias 29, 154 51 Neo Psichiko, Athens, Greece.
2. Orthopaedic Department Royal United Hospital, Bath BA1 3NG, Somerset, UK.
3. Athens Medical Centre, Andersen 1, 11525 Athens, Greece.
4. Biostatistics Laboratory, Department of Social Medicine University of Crete, 71409 Heraklion, Crete, Greece.