What is wrong with the Stryker ABGII—Are Problems Due to Mismatched Components?

When the Stryker ABGII recall occurred in July, 2012, there were many recipients of the hip implant as well as surgeons who implanted the ABGII who were left wondering how an unsafe device had been implanted in over 9,000 people. Soon after the ABGII received FDA approval in 2009, adverse events were reported to the agency. In April, prior to the recall in July, Stryker issued an Urgent Field Safety Notification, warning surgeons and hospitals of the increased risks of corrosion and fretting of the ABGII. This corrosion can lead to the excess generation of cobalt and chromium ions, causing those metal shards to enter the body. Stryker also noted a higher-than normal rate of failure for the ABGII. The manufacturer did imply, however, that the problems associated with the ABGII could be attributed to surgeon error or patient issues such as extreme sensitivity to metals, being overweight, or having a previous health condition which caused the corrosion. Stryker did not mention the fact that when the ABGII is implanted, the Morse taper is hammered into the stem, potentially releasing cobalt and chromium ions into the body.

Stryker ABGII Mismatched Components and the Resulting Problems

Therefore, even though the design of the ABGII was originally believed to be much safer than that of other all-metal hip implants, those beliefs were not upheld once the ABGII was implanted. Unlike other all-metal hip implants the ABGII used a ceramic ball rather than a cobalt and chromium ball. Further, while using a cobalt and chromium neck and a titanium stem, Stryker sprayed those components with a proprietary TMZF coating, claiming this would alleviate the problems associated with mismatched components. Again, this claim turned out to be less than true. It is hard to understand why Stryker designed the ABGII using mismatched components since research from over a decade ago warned of the increased levels of corrosion when dissimilar metals come into contact. Scientists believe that because the cobalt and chromium neck component is much harder than the titanium stem, excess corrosion can result.

One study done over a decade ago noted that moderate to severe corrosion was seen in up to 28% of similar alloy hip implants while 42% of implants using mixed alloys showed signs of corrosion. In another study, implants removed from patients showed significant levels of corrosion among those of mixed metals while those which implemented similar metals showed little or no corrosion. In scientific terms, the active metal (titanium) or anode is attacked by the cathode—the more resistant metal, and, in this case, the cobalt and chromium neck. This is known as galvanic corrosion, and while some metals form a sort of film once they are implanted in the body—which would theoretically protect the implant recipient from the effects of mismatched components—this film only remains present and protective when there is no motion or wear. This means that the film would only be protective if the implant recipient never engaged in any sort of activity. Cobalt and chromium has a hardness factor of 4.5 GPa (gigapascal) as opposed to titanium, which has a hardness factor of 3.0 GPa. (One gigapascal is equal to 140,000 psi).

Stryker ABGII Design Problems

Despite what appeared to be an innovative design on the part of Stryker at the time the ABGII was released, the implant did not live up to the expectations. Stryker claimed the implant would last as long as twenty years, yet scores of patients were forced to have their ABGII implant