Findings From 333 Retrieved MoM Total Hip Arthroplasty Components of a Single Design Reveal Modular Interface Corrosion as Most Common Feature.

Abstract

High revision rates and adverse reactions to metal debris led to the discontinuation of most metal-on-metal (MoM) hip systems nearly a decade ago, including the DePuy Pinnacle. This study presents the largest retrieval analysis of this design, investigating relationships among femoral head and acetabular liner taper corrosion, bearing surface wear, and implant design features. All 333 retrieved Pinnacle MoM implants from North America, Australia, and Japan, collected between 2013 and 2023, were inspected. Taper corrosion was assessed using the Visual Grading System. Bearing surface wear and diametral clearance were quantified using coordinate measuring techniques. Correlations between taper damage, bearing wear, clearance, and time in vivo were evaluated using nonparametric statistical tests. Components were in vivo for a median of 5 years (1 day to 14 years). Median combined volumetric wear was 6.9 mm3 (0.5 to 568.9 mm3), and the median wear rate was 1.8 mm3/yr (0.1 to 191.0 mm3/yr). Moderate or severe corrosion (Visual Grading System ≥ 4) was observed in 60% of head tapers, with severity correlated with time in vivo (P < 0.01). Smaller taper diameters, particularly mini tapers, exhibited higher corrosion scores (P < 0.01). Flexural rigidity ranged from 30.5 to 389.0 N·m2, and more flexible tapers correlated with higher corrosion scores (P < 0.01). Combined volumetric wear correlated with time in vivo (P < 0.01), whereas lower clearance was associated with reduced wear rates (P < 0.01). High-clearance components (>100 µm) showed markedly greater wear and liner taper corrosion (P < 0.01). The results indicate that higher head/liner clearance was associated with higher volumetric wear and higher liner taper corrosion, but not with head taper corrosion. Although causality is difficult to establish, low femoral stem taper flexural rigidity and high clearance were likely the most important factors resulting in the failures in this cohort.