2017 HIP SOCIETY PROCEEDINGS
Where Are We Now?
Regulatory authorities recommend regular surveillance and early revision of metal-on-metal hip replacements (MoMHR) for adverse reactions to metal debris (ARMD) [6, 13]. These recommendations have contributed to an increased number of revisions for ARMD [1, 2, 6, 13].
According to the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man, 19% of patients with stemmed MoMHR underwent revisions in 12 years , while 14% of patients with resurfacing MoMHR underwent revisions in that same time frame . This implies that over 80% of more than one million MoMHRs implanted worldwide remain in service, and so should be followed closely, as they are at risk for complications (some of which do not cause symptoms) that could warrant revision surgery [3, 4, 8]. However, we do not know which of those patients, if any, should undergo revision, particularly those who are not symptomatic but who may have either elevated levels of metal species in blood or serum, or who have abnormal findings on advanced imaging tests [3, 4].
The current study by Matharu and colleagues analysed the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man to compare the group of patients undergoing revision for ARMD with those who underwent revision for other reasons, uniquely matched by propensity scores. Their findings contradicted previous reports suggesting that MoMHR revisions for ARMD had a higher risk of complications and reoperations compared to non-ARMD revisions [1, 7, 11].
Where Do We Need To Go?
These findings raise a number of important questions including: (1) Are the assessments made after MoMHR revisions as stringently applied as before the revisions? (2) What is the threshold for MoMHR rerevisions after ARMD? It is also worth noting that 10-year rerevison risk following total hip replacement revisions is 15%, approximately three times higher than the revision risk for primary total hip replacements .
Additionally, we still need to determine (1) the ideal threshold for MoMHR revisions, (2) the most-practical surgical techniques and implants for performing these revisions, (3) surgical approaches to these revisions that minimize the risk of dislocation, infection, and other complications [10-12], and (4) correlation of clinical, biochemical and radiological findings before revision with patient-reported and/or validated outcomes tools before and after revision.
How Do We Get There?
Researchers should conduct both retrospective database studies and multicenter prospective studies that examine large numbers of MoMHR revisions and rerevisions. These studies should focus on revision indications like ARMD, prosthetic joint infection, and dislocations/instability. Although long-term survivorship of revision resurfacing MoMHR has been documented , long-term studies on stemmed MoMHR revisions have yet to emerge. Additionally, studies that correlate the relationship between clinical, biochemical, and radiological findings with patient-reported and/or validated outcomes tools before and after revisions can potentially help evolve robust MoMHR revision criteria, risk score indices, and perhaps an algorithm for guiding revisions and rerevisions. Revisions for prosthetic joint infection after MoMHR remain a challenge for surgeons, but basic studies on biofilm eradication, immune enhancement with immunotherapy or modulation, genetic modulation and antibiotic delivery systems  could offer a pathway to successful treatment options. In the interim, clinical research should continue to evaluate patient management approaches for those with infected MoMHRs, including the use of débridement, antibiotics, implant retention, and single-stage and staged revisions.
1. De Smet KA, Van Der Straeten C, Van Orsouw M, Doubi R, Backers K, Grammatopoulos G. Revisions of metal-on-metal hip resurfacing: Lessons learned and improved outcome. Orthop Clin North Am. 2011;42:259–269.
2. Grammatopoulos G, Pandit H, Kwon YM, Gundle R, McLardy-Smith P, Beard DJ, Murray DW, Gill HS. Hip resurfacings revised for inflammatory pseudotumour have a poor outcome. J Bone Joint Surg Br. 2009;91:1019–1024.
3. Hussey DK, Madanat R, Donahue GS, Rolfson O, Bragdon CR, Muratoglu OK, Malchau H. Scoring the current risk stratification guidelines in follow-up evaluation of patients after metal-on-metal hip arthroplasty: A proposal for a metal-on-metal risk score supporting clinical decision-making. J Bone Joint Surg Am. 2016;98:1905–1912.
4. Kwon YM, Lombardi AV, Jacobs JJ, Fehring TK, Lewis CG, Cabanela ME. Risk stratification algorithm for management of patients with metal-on-metal hip arthroplasty: consensus statement of the American Association of Hip and Knee Surgeons, the American Academy of Orthopaedic Surgeons, and the Hip Society. J Bone Joint Surg Am. 2014;96:e4.
5. Matharu GS, Pandit HG, Murray DW. Poor survivorship and frequent complications at a median of 10 years after metal-on-metal hip resurfacing revision. Clin Orthop Relat Res. 2017;475:304–314.
7. Munro JT, Masri BA, Duncan CP, Garbuz DS. High complication rate after revision of large-head metal-on-metal total hip arthroplasty. Clin Orthop Relat Res. 2013;472:523–528.
9. Parvizi J, Haddad FS. Periprosthetic joint infection: The last frontier. Bone Joint J. 2015;97:1157–1158.
10. Penrose CT, Seyler TM, Wellman SS, Bolognesi MP, Lachiewicz PF. Complications are not increased with acetabular revision of metal-on-metal total hip arthroplasty. Clin Orthop Relat Res. 2016;474:2134–2142.
11. Rajpura A, Porter ML, Gambhir AK, Freemont AJ, Board TN. Clinical experience of revision of metal on metal hip arthroplasty for aseptic lymphocyte dominated vasculitis associated lesions (ALVAL). Hip Int. 2011;21:43–51.
12. Snir RN, Park BK, Garofolo G, Marwin SE. Revision of failed hip resurfacing and large metal-on-metal total hip arthroplasty using dual-mobility components. Orthopedics. 2015;38:369–374.