1. Department of Orthopaedics and Rehabilitation, Hospital Universitario Central de Asturias, Celestino Villamil s/n, 33006 Oviedo, Asturias, Spain.
2. Department of Orthopaedics and Rehabilitation, University of Iowa Hospitals and Clinics, 01006 JPP, 200 Hawkins Drive, Iowa City, Iowa 52242, USA.