Adverse reaction to local metal debris does not always come from metal on metal bearing wear

Abstract

Introduction Abnormal metal ion release from wear of metal-on-metal (MoM) bearing in total hip arthroplasty (THA) is associated with adverse local reactions to metal debris (ARMD). Metal particles may also arise from wear and corrosion of the implant's modular junction. The aim of this study was to compare ion levels and rate of ARMD between patients with THA sharing the same MoM bearing but one group having monoblock stems versus another group having modular stems. Materiel et methodes This study included 45 patients who underwent primary MoM THA using the same acetabular component and large diameter metallic modular femoral head. 32 hips received a modular stem and 13 hips received a monoblock stem. Cobalt (Co) and chromium (Cr) ion concentrations, ARMD rate and function measured by UCLA and WOMAC scores were compared between groups. Resultats ARMD rate was significantly lower in the monoblock group (16%) compared to the modular group (46%, P = 0.031). Revision for ARMD was performed at 115 ± 5.9 months after primary THA in the monoblock group versus 63 ± 2.3 months in the modular group. ARMD cases had severe wear and corrosion of the junction between stem and femoral head trunnion in all monoblock cases and the junction between stem and modular neck in all the modular ones. Cr and Co ions levels were significantly lower in the monoblock stem group: 2.0 ± 1.0 μg/L vs. 7.2 ± 11.4 μg/L (P Discussion The rate of ARMD was significantly higher in the modular stem group and this group required revision earlier. Although both groups had MoM bearings, corrosion at stem/neck or neck/head junctions were seen as the source of excessive metal ions release lea. Conclusion In the presence of ARMD, MoM bearing wear may not be the main source of failure. Modular junction's poor performances may be more deleterious than the bearing. To avoid such complication, THA femoral stem modular junctions should be eliminated (return to a full monoblock implant) or have improved junction design.