Corrosion at the cone/taper interface leads to failure of large-diameter metal-on-metal total hip arthroplasties

Abstract

Background: Metal-on-metal (MoM) THAs have reduced wear rates compared with metal-on-polyethylene. However, elevated serum metal ion levels and pseudotumors have been reported in large MoM articulations.

Questions/purposes: We therefore determined (1) if corrosion occurred at the cone/taper interface leading to instability in patients with large-diameter THAs; (2) how patients presented clinically and radiographically; (3) if adverse periprosthetic tissue reactions occurred; (4) whether metal was released from the implants into the periprosthetic tissues; and (5) if head size correlated with metal release.

Methods: We reviewed 114 patients who had revisions of large-diameter head MoM articulations. Mean time of implantation was 46 months. To identify adverse reactions and particle load, tissues were stained by hematoxylin and eosin and CD3/CD20/CD68 antibodies. Periprosthetic tissues were analyzed for metal content and distribution in different regions. Electrochemical reactions between the stem and adapter were investigated by a minicell electrode.

Results: Electrochemical studies on the stem and the head adapter showed a risk for galvanic corrosion. Ninety-four percent of patients had instability at the cone/taper interface. All patients presented with early clinical symptoms; 59 patients had radiographic signs of loosening. One hundred four patients had foreign body reactions and necrosis. The largest amounts of metal released were titanium or iron. We found no correlation between head size and metal ion release.

Conclusions: These findings suggest that in modular cone/taper connections, friction of the MoM articulations may cause failure of the cone/taper interface leading to galvanic corrosion and loosening. It is unclear whether the design of this MoM system provides sufficient stability at the taper.

Fig. 1

The intraoperative photograph shows the implant components after disassembling of the loose cone/taper connection with surrounding granulation tissue.

Fig. 2

Higher magnification photograph shows corrosive changes at the cone and granulation tissues curetted from the osteolysis of the proximal femur.

Fig. 3

The intraoperative photograph demonstrates the osteolysis cleared of granulation tissue and its extension into the proximal femur.

Fig. 4A–C

(A) This is a section of retrieval tissue dominated by monocytes (Stain, hematoxylin & eosin [H&E]; original magnification, ×20). (B) Perivascular infiltration by lymphocytes was observed as described by Willert et al. [42] (Stain, CD20; original magnification, ×20) (C) Necrosis is seen in the revision tissues (Stain, H&E; original magnification, ×20).

Fig. 5

The released metals were determined in the different regions of the revision tissues from failed THAs. The highest metal content of Fe and Ti is found in the bursa and capsule.

Fig. 6

Head size (mm) does not correlate with tissue metal content for each patient.