Abstract
The articulating surface replacement (ASR) XL stemmed total hip replacement and ASR resurfacing hip systems were recalled by DePuy due to a high prevalence of early failure. The ASR XL has a greater failure rate than the ASR resurfacing, which has been increasingly attributed to wear and corrosion at the taper interface between the female taper surface of the femoral head and the male taper (trunnion) of the femoral stem. The aim of this study was to quantify the prevalence and severity of taper corrosion in retrieved ASR XL hip components.
A peer-reviewed subjective corrosion scoring system was used to quantify corrosion in a consecutive series of the 50 ASR XL hip components (head components – n=44; femoral stems – n=6) at our retrieval centre. Bearing surface wear (femoral head and acetabular cup combined) was quantified and a value of <5 microns was defined as low-wearing. Subsequent profilometry analysis was undertaken in the low-wearing hips to quantify material loss from the taper interface.
90% of components showed evidence of corrosion, with at least moderate corrosion observed in 58%. There were 17 low-wearing hips which had a median material loss from the taper interface of 3.51mm3 (range: 0.612–9.443). The median linear depth of material loss was 33μm (range: 8.5–78.0). No relationship was observed between taper corrosion and serum cobalt (r=0.204, p=0.2712) or chromium (r=0.146, p=0.432) metal ions.
Wear and material loss from metal-on-metal (MoM) hips is associated with pseudotumour formation and adverse soft-tissue reactions. We have shown that taper corrosion is extremely common in failed ASR XL hips and that wear occurs in the same degree of magnitude as at the bearing surface also occurs at the taper interface. Therefore our findings support the emerging concept of ‘taper failure’, whereby the taper is the predominate reason for failure of MoM hips. Future work must determine the relative contributions of the bearing surface and the taper interface to serum cobalt and chromium metal ion levels.
