What Are Normal Metal Ion Levels After Total Hip Arthroplasty? A Serologic Analysis of Four Bearing Surfaces

Abstract Background The recent experiences with adverse local tissue reactions (ALTR) have highlighted the need to establish what are normal serum levels of cobalt (Co), chromium (Cr), and titanium (Ti) after hip arthroplasty. Methods Serum Co, Cr, and Ti levels were measured in eighty nonconsecutive patients with well-functioning unilateral THA and compared among four bearing surfaces: ceramic on ceramic (CoC); ceramic on polyethylene (CoP); metal on polyethylene (MoP), and dual mobility (DM). The preoperative and most recent UCLA and WOMAC scores were compared among the different bearing surfaces. Subgroup analysis was also completed using metal vs. ceramic heads to compare metal ion levels and patient reported outcomes. Categorical variables were compared among the four bearing couples using Fisher exact tests and between metal and ceramic heads using Chi-squared tests. Continuous variables were compared between bearing surface groups using Kruskal–Wallis tests and between metal and ceramic heads using Wilcoxon rank-sum tests. Spearman correlation coeffecient was used measure the correlation between PROM and metal ion levels. Results No significant difference was among serum Co and Cr levels between the four bearing surface groups (p= 0.0609 and p= 0.1577). The preoperative and most recent UCLA activity and total WOMAC scores were not significantly different among different bearing surfaces. Secondary analysis comparing metal and ceramic femoral heads demonstrated that the metal group (MoP, MDM (metal)) had significant higher serum Co levels compared to the ceramic group (CoC, CoP, MDM (ceramic)) (1.05 μg/L +/- 1.25 vs 0.59 μg/L +/- 0.24; p=0.0411). No statistical differences in UCLA or WOMAC scores were noted between the metal vs. ceramic head groups at baseline or at latest follow up. No differences in Co and Cr levels were seen among different trunnion designs (p=0.6921; p=0.7876, respectively). Serum Cr was higher with polyethylene acetabular liners compared to ceramic acetabular liners (0.69 μg/L (±0.44) vs 0.5 μg/L (±0.0), p=0.0421). No difference was seen in Co levels among acetabular liner types (p=0.93). Spearman coefficient identified no correlation between metal ion levels and PRO scores. Conclusions No serum metal ion level differences were found among well-functioning total hip arthroplasty with modern bearing couples. Significantly higher serum Co levels were seen when comparing metal vs. ceramic femoral heads in this study and warrants fu