Data recorded includes medical outcome scores (WOMAC and MOS SF-36), patient data, operative details (including type of prostheses used and operative technique employed), inpatient course, and any postoperative events. For revision procedures, additional data such as location of bony defects (Gruen zones) and acetabular bone loss (Paprosky classification) are also recorded. Follow up in a special Joint Register Clinic is at six months, two years and every five years thereafter for primary procedures. This is reduced to every two years in the case of revision procedures. To date, a pilot study involving four surgeons has prospectively captured data on 82 patients undergoing both primary and revision procedures in our unit. We aim to enrol all our patients in the register from July 2005, increasing the amount of data collected, which we hope will subsequently benefit patients undergoing hip and knee arthroplasty in the future.