In Vivo Corrosion of Modular Dual-Mobility Implants: A Retrieval Study

Modular dual-mobility (MDM) total hip arthroplasty (THA) implants have an additional metal-metal interface between the metal liner and outer metal shell that poses a risk of corrosion. The purpose of this study is to evaluate retrieved MDM liners to evaluate qualitative and quantitative damage and corrosion patterns at this interface.

Twelve MDM implants of one design with a mean in situ duration of 26 months (range, 1-57 months) were evaluated. Six implants (50%) were from primary THAs and 6 (50%) from revision THAs. The taper region of the liner at risk of damage was qualitatively graded using modified Goldberg criteria while quantitative dimensional assessment was performed with a validated coordinate measurement machine.

Among the retrieved implants, 2 (17%) demonstrated severe grade 4 corrosion, 5 (42%) moderate grade 3 corrosion, 4 (33%) mild grade 2 corrosion, and 1 (8%) grade 1 (no visible corrosion). Mean maximum linear corrosion depth at the taper interface measured 35.5 microns (range, 8.4-176.2 microns). All implants had a maximum linear corrosion depth >7 microns, a threshold suggestive of potentially clinically significant material loss. Three corrosion patterns were identified: generalized corrosion, a stripe of corrosion about the middle of the taper region, and focal areas of corrosion at the portion of the taper closest to the joint surface.

Visual and dimensional analysis of all 12 retrieved MDM implants demonstrated identifiable corrosion/wear of the cobalt-chromium metal liner taper of varying severity. These implants should be used judiciously until larger series with clinical correlation can be completed.