Abstract
Introduction
Wear debris generation in metal-on-metal (MOM) total hip arthroplasty (THA) has emerged as a compelling issue. In the UK, clinically significant fretting corrosion was reported at head-taper junctions of MOM hip prostheses from a single manufacturer (Langton 2011). This study characterizes the prevalence of fretting and corrosion at various modular interfaces in retrieved MOM THA systems used in the United States.
Methods and Materials
106 MOM bearing systems were collected between 2003 and 2012 in an NIH-supported, multi-institutional retrieval program. From this collection, 88 modular MOM THA devices were identified, yielding 76 heads and 31 stems (22 modular necks) of 7 different bearing designs (5 manufacturers) for analysis. 10 modular CoCr acetabular liners and 5 corresponding acetabular shells were also examined. Mean age at implantation was 58 years (range, 30–85 years) and implantation time averaged 2.2 ± 1.8 years (range, 0–11.0 years). The predominant revision reason was loosening (n=52). Explants were cleaned and scored at the head taper, stem taper, proximal and distal neck tapers (for modular necks), liner, and shell interfaces in accordance with the semi-quantitative method of Goldberg et al. (2002).
Results
Fretting and corrosion were observed on 68/76 (89%) head tapers, 21/31 (68%) stem tapers, 15/22 (68%) proximal modular neck tapers, 20/22 (91%) distal modular neck tapers, 10/10 (100%) modular liners and 5/5 (100%) modular shells. Scores were lower at proximal stem tapers than within the head tapers (p = 0.001) but were positively correlated (ρ = 0.56, p = 0.001). At the head-neck interface, significantly more damage was noted on head tapers of devices with modular necks (p<0.001). At the neck-stem interface, damage to modular necks was localized at the curved medial and lateral surfaces. A significant correlation was observed between implantation time and corrosion/fretting score at this region (ρ = 0.78, p < 0.001). Damage was noted at all shell-liner interfaces, manifested primarily as scratching with discoloration on the backside rim of liners and circular fretting patterns on shells.
Discussion
These results support the inclusion of fretting and corrosion evaluation in standardized MOM retrieval inspection protocols. Adaptation of the method developed by Goldberg and colleagues is suitable for the variety of modular connections in contemporary MOM THA implants, which may incorporate modular femoral and/or acetabular components. Further quantitative assessment of wear at modular interfaces of retrieved MOM devices is therefore warranted.
