586 THE JOURNAL OF BONE AND JOINT SURGERY Metal ion levels after metal-on-metal Ring total hip replacement A 30-YEAR FOLLOW-UP STUDY P. Sauvé, J. Mountney, T. Khan, J. De Beer, B. Higgins, M. Grover From the Queen Alexandra Hospital, Portsmouth, England  M. Grover, FRCS, Consultant Orthopaedic Surgeon  P. Sauvé, MRCS, Specialist Registrar, Wessex  J. Mountney, FRCS(Trauma & Orth), Specialist Registrar, Wessex  T. Khan, MRCS, Specialist Registrar, Wessex  J. De Beer, FCSOrtho (SA), Hip Arthroplasty Fellow Portsmouth Hospitals NHS Trust, Queen Alexandra Hospital, Southwick Hill Road, Cosham PO6 3LY, United Kingdom.  B. Higgins, BSc, Senior Lecturer in Medical Statistics University of Portsmouth, School of Health Sciences and Social Work, Gloucester House, Queen Alexandra Hospital, Southwick Hill Road, Cosham, Portsmouth PO6 3LY, United Kingdom. Correspondence should be sent to Mr P. Sauvé; e-mail: philsauve@doctors.org.uk ©2007 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.89B5 18457 $2.00 J Bone Joint Surg [Br] 2007;89-B:586-90. Received 27 July 2006; Accepted after revision 15 January 2007 Metal-on-metal bearings for total hip replacement (THR) are becoming increasingly popular. Improved wear characteristics mean that these articulations are being inserted into younger patients in the form of THR and resurfacing procedures. This has led to concerns regarding potential carcinogenicity because of the increased exposure to metal ions that the procedure brings. We have studied the serum cobalt and chromium concentrations in patients who had primary, well-fixed Ring metal-on-metal THRs for more than 30 years. The levels of cobalt and chromium were elevated by five and three times, respectively compared with those in our reference groups. Metal-on-metal articulations appear to be the source of metal ions throughout the life of the prosthesis. In three patients who had undergone revision of a previous metal-on-metal THR to a metal-on-polyethylene replacement the levels of metal ions were within the normal range. The elevations of cobalt and chromium ions seen in our study were comparable with those in patients with modern metal-on-metal THRs. Some first-generation metal-on-metal hip replace- ments have now reached their third decade. Osteolysis is recognised as a significant compli- cation of metal-on-polyethylene articulations and this has precipitated renewed interest in metal-on-metal implants. 1 Ring 2 used this bearing surface and first described it in 1968. The Ring total hip replacement (THR) (Downs Bros, Mitcham, United Kingdom) was designed for implantation without acrylic cement. The acetabular component consisted of an articular surface with a threaded stem 75 mm long and 9.5 mm in diameter which was inserted along the iliopubic bar so that it followed the weight-bearing line of the proxi- mal femur. Prostheses were manufactured from a cast alloy of cobalt, chromium and molybdenum with a relatively high carbon content of 0.25%. This cobalt-chromium alloy was not heat-treated. The Ring prosthesis showed rates of aseptic loosening of up to 15.7% at a follow-up of 2.5 years. 3 The femoral component was particu- larly prone to loosening. A long-term follow- up study by Ring 2 showed survivorship, with revision as the end-point, ranging between 68% and 95% at 15 years. Various factors led to these prostheses being abandoned in favour of metal-on-polyethylene THR. Early failure of many Ring THRs was attributed to poor matching between the femoral and acetabular components resulting in clutching of the head in the socket. 3 Concerns have been expressed regarding the carcinogenic potential of metal ions produced from wear of these metal-on-metal articula- tions. 4-6 Both in vivo and in vitro studies have demonstrated chromosomal abnormalities in the presence of increased levels of cobalt and chromium. 7,8 Our study therefore aimed to investigate whether metal ions continue to be produced throughout the life of the prosthesis. Patients and Methods Between 1968 and 1974, we inserted 310 THRs using the Ring metal-on-metal articula- tion. In 241 hips the indication for THR was osteoarthritis, in 56 failure of a previous hip operation and in seven rheumatoid arthritis. The mean age of the patients at the time of sur- gery was 64.5 years (30 to 86). The patients were traced using the on-line National Health Service Strategic Tracing Ser- vice. 9 This is a database of people, places and NHS organisations in England and Wales. Access to this resource is through approved organisations only, such as NHS trusts, primary-care trusts, strategic health authori- ties, etc. Our local ethics committee gave approval for the study. Hip