A new study published in January has found that the rate of metal-on-metal (MoM) hip implant patients undergoing revision (or re-do) surgery has increased over time. The observed differences are in part due to increased patient surveillance and a lowering of the threshold for further surgery, researchers at the Universities of Oxford and Bristol have suggested.
Approximately 1.5 million patients worldwide have received metal-on-metal hip replacements for painful arthritis. Abnormal reactions to metal can develop which may cause surrounding tissue damage and many patients with these reactions require further operations. Worldwide authorities recommend that patients with a MoM hip implant undergo regular hospital check-ups, blood tests, and/or imaging to monitor their condition.
Using data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR) researchers examined the five-year revision rates for MoM hips implanted from 2007 onwards and compared them to MoM hips implanted before 2007. The results show a significant increase in revision surgery for all primary MoM hip replacement designs implanted from 2007 onwards compared to surgeries performed before 2007.
On the study’s findings, one of the authors, Gulraj Matharu of the University of Oxford, commented: “The increased number of metal-on-metal hip implant patients undergoing further surgery in recent years is likely explained by changes made in how this group of patients are managed. Our study findings are most likely attributable to the increase in regular patient follow-up combined with many surgeons now acting earlier to perform revision surgery.
“Reassuringly, the study’s findings support the current national surveillance guidance for metal-on-metal hip implant patients. There are still many patients who have metal-on-metal hip replacements and therefore it is important to repeat the analysis of registry data in the future to determine whether these findings change with extended follow-up.”
Commenting on the relationship between the NJR and regulatory bodies, Professor Ashley Blom, from the University of Bristol who leads the NJR data analysis team, commented: “Since the NJR first began identifying problems with all types of metal-on-metal hip prostheses, we have been working closely with the Medicines and Healthcare Products Regulatory Agency and the British Orthopaedic Association to ensure that all patients are monitored and cared for appropriately.
“This has resulted in increased awareness of potential problems and increased surgical experience for hip revision surgery performed for abnormal reactions to metal. It is therefore unsurprising that revision rates for all types of metal-on-metal prostheses have been rising over time, reflecting that hospitals and surgeons are intervening in a timely manner.”
Source: National Joint Registry
Reference: Matharu G. S., et al., ‘Is the rate of revision of 36 mm metal-on-metal total hip arthroplasties with Pinnacle acetabular components related to the year of the initial operation?’, Bone and Joint Journal (published 5 January 2018)