Levels of metal ions after small- and large-diameter metal-on-metal hip arthroplasty

Abstract

etal-on-metal (MOM) bearings for hip arthroplasty are increasing in popularity. Concern remains, however, regarding the potential toxicological effects of the metal ions which these bearings release.The serum levels of cobalt and chromium in 22 patients who had undergone MOM resurfacing arthroplasty were compared with a matched group of 22 patients who had undergone 28 mm MOM total hip arthroplasty (THA).At a median of 16 months (7 to 56) after resurfacing arthroplasty, we found the median serum levels of cobalt and chromium to be 38 nmol/l (14 to 44) and 53 nmol/l (23 to 165) respectively. These were significantly greater than the levels after 28 mm MOM THA which were 22 nmol/l (15 to 87, p = 0.021) and 19 nmol/l (2 to 58, p < 0.001) respectively.Since the upper limit for normal patients without implants is typically 5 nmol/l, both groups had significantly raised levels of metal ions. MOM bearings of large diameter, however, result in a greater systemic exposure of cobalt and chromium ions than bearings of small diameter. This may be of relevance for potential long-term side-effects. It is not known to what extent this difference is due to corrosion of the surfaces of the component or of the wear particles produced. MMetal-on-metal (MOM) bearings were first used in total hip arthroplasty (THA) over 40 years ago.1-3 Because of a limited understanding of the engineering of these bearings and early failures in some cases, they lost popularity to the lowfriction stainless-steel/ultra-high-molecular-weight polyethylene bearing developed by Charnley. 4 Over the past 15 years, with an improved understanding of the aetiology of aseptic loosening and of the science of wear, there has been increased interest in the use of MOM bearings. 5,6 Of the many engineering factors which have contributed to the success of the MOM bearing, the metallurgy, diametric bearing clearance, sphericity and surface finish are thought to be most important. 7-9All metal implants, especially those which include MOM bearings corrode at a rate determined, in part, by their surface area. 10 Further, side-effects relate directly to the particles of metal which are produced and their subsequent fate within the body. Our hypothesis was that the production of wear debris, and thus metal ion release, would be less after resurfacing arthroplasty than after THA using a 28 mm MOM bearing. This was based on the theoretical fluid film lubrication and reduced potential for the production of wear debris which is thought to occur in MOM bearings of large diameter, despite the increased surface area available for corrosion with these implants. 11 Patients and MethodsEvaluation of patients. All joint arthroplasties are prospectively registered on a computerised database. We contacted patients who had undergone either unilateral MOM or resurfacing arthroplasty at least six months earlier and asked them to attend dedicated clinics. They completed a questionnaire and provided a sample of blood for analysis of cobalt and chromium. Since we were interested in estima...

Do Ion Levels In Hip Resurfacing Differ From Metal-on-metal THA at Midterm?

“…Although there are no published reports which directly compare ion levels in patients with MOM-BHR or MOM-THA, our data are in the range previously reported. Some authors have evaluated ion levels, but the studies either had short-term followup or they were not comparative studies of MOM-BHR versus MOM-THA (Table 4) [3,5,11,17,27,29,34,38,39]. In addition, we found time of followup and age had no influence on serum ion levels, whereas gender in association with implant type influenced Cr levels, with females who had MOM-BHR showing an increase in Cr levels compared with males who had MOM-BHR.…”

“…All metal implants corrode at a rate which is determined partly by their surface area [4]. For this reason, the introduction of large-diameter MOM bearings, as used in MOM-BHR, has prompted even more concern [5]. However, the large diameter and low radial clearance of MOM bearings are key factors in reducing dry contact and hydrodynamic pressures and important in improving lubrication performance [25].…”

Does Ion Release Differ Between Hip Resurfacing and Metal-on-metal THA?

“…The trend in our results also agrees with that reported by Daniel et al [6] for the same followup in a study of BHR with bearing diameters of 50 mm and 54 mm versus 28-mm Metasul 1 MOM THA, in which whole blood samples were analyzed. In contrast, Clarke et al [5], at a median of 16 months, reported higher median Co and Cr serum levels in patients who had hip resurfacing arthroplasty compared with patients who had MOM THAs. Unlike our study, Clarke et al [5] used two different prosthetic designs.…”

“…In contrast, Clarke et al [5], at a median of 16 months, reported higher median Co and Cr serum levels in patients who had hip resurfacing arthroplasty compared with patients who had MOM THAs. Unlike our study, Clarke et al [5] used two different prosthetic designs. One was the double heat-treated Cormet 2000 TM (Corin Group PLC, Cirencester, UK) (carbide volume fraction, 2.3%) and the other was the as-cast BHR (carbide volume fraction, 5%).…”

“…Metal-on-metal (MOM) total hip resurfacing offers a suitable solution for young and/or active patients affected by osteoarthritis, osteonecrosis, epiphysiolysis, congenital hip dysplasia, and rheumatoid arthritis, but the large surface area of large diameter implants raises concerns regarding postoperative metal ion release [5]. Potential effects of chronic increases in serum Co and Cr levels include local tissue toxicity, inflammation, bone loss, renal function alteration, immune modulation, hypersensitivity, chromosomal damage, and malignant cellular transformation [20,27,36,41].…”