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

Abstract

Modern metal-on-metal hip resurfacing was introduced as a bone-preserving method of joint reconstruction for young and active patients; however, the large diameter of the bearing surfaces is of concern for potential increased metal ion release. We hypothesized there were no differences in serum concentrations of chromium, cobalt, and molybdenum between patients who had metalon-metal hip resurfacing (Group A; average head diameter, 48 mm; median followup, 24 months) and patients who had 28-mm metal-on-metal THA (Group B; median followup, 25 months). Serum concentrations also were compared with concentrations in healthy subjects. We identified no differences in ion levels between Groups A and B. A distinction was made according to gender. Women showed a higher chromium release in Group A whereas men had a higher cobalt release in Group B. Values obtained from Group A were higher than those of the control subjects. Our data suggest metal-on-metal bearings for THA should not be rejected because of concern regarding potential increased metal ion release; however, patients with elevated ion levels, even without loosening or toxicity, could be at higher risk and should be followed up periodically. Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

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.…”

“…Theoretical and experimental studies, however, suggest metal wear may increase serum metal ion levels, which would be a cause for concern, particularly in the long term. A previous short-term study suggested that there were no differences in metal ion concentrations between large-diameter MOM-BHR bearings and small-diameter MOM-THA bearings [27]. Data from the same comparison at medium term are lacking.…”

“…Nonetheless, concerns have been raised regarding increased postoperative serum metal ion concentrations [20]. A previous study of Cr, Co, and Mo values in patients treated with either MOM-BHR or MOM-THA showed higher serum metal ion levels in both groups compared with those of control subjects but no differences between the two implant groups at a followup of 2 years [27]. The same comparison has not been made at medium term, and confounding factors, such as gender, time of followup, and age in association with implant type have not been considered.…”

Acetabular Component Thickness Does Not Affect Mid-term Clinical Results in Hip Resurfacing

“…This was expected because the bearing characteristics of the two acetabular components were identical and the manufacturing tolerances for roundness and clearance were the same. In addition, the median values for serum cobalt and chromium were as low as any previously reported for any type of hip resurfacing design [1,16,21,22,28].…”

What Are the Risks Accompanying the Reduced Wear Benefit of Low-clearance Hip Resurfacing?

“…Laboratory results [1,37] and clinical metal ion [3,12,31] studies relating to the effect of bearing diameter on wear and metal ions suggest conflicting conclusions, with some showing an inverse relationship between bearing diameter and wear and others showing no effect. Several in vitro studies relating to the effect of clearance [14,20,35,36] on wear also reported conflicting results.…”