1. Orthopaedic Surgery, SUNY-Upstate Medical University, 550 Harrison St, Suite 128, Syracuse, New York 13202, USA.
2. The Orthopaedic Research Unit, Cambridge University, Cambridge CB2 2QQ, UK.
3. The Cambridge Hip and Knee Unit, BUPA Cambridge Lea Hospital, 30 New Road, Impington, Cambridge CB4 9EL, UK.