How Many Victims of Stryker ABGII Design Problems Are There?

Following the recall of the Stryker ABGII in July, 2012, many wondered just how many victims of the defective hip implant there really were.  The Stryker Corporation is a Fortune 500 Company, with an estimated worth of over $20 billion dollars. It is estimated that over 9,000 people were implanted with an ABGII device between the time it gained FDA approval in 2009 and the time of the recall.

Stryker ABGII Defects

While the ABGII device is not a true all-metal implant, it has nonetheless experienced the same types of problems as other metal-on-metal devices. The ABGII uses a ceramic ball, rather than a metal ball, which led patients and surgeons to believe it was a much safer alternative to the all-metal implants. The ABGII is composed of a variety of stem and neck components rather than the traditional one-piece design. This design allows surgeons to more precisely fit the hip implant to the individual patient, according to body size and type as well as level of activity.

Despite the ceramic ball and the innovative design of the ABGII, very little time passed after marketing of the device began and the time implant recipients began experiencing problems related to their implant. In 2010 alone, the FDA received at least 60 adverse events involving an ABGII hip implant or a Stryker Rejuvenate which was also recalled at the same time as the ABGII. By the end of 2011, the number of adverse reports to the FDA regarding the ABGII hip implant had risen to 130, and by the beginning of 2012, to over 300.

Was Stryker Aware of the Problems with the ABGII?

Failures of ABGII hip implants in other countries were climbing as well; The Australian Registry calculated a failure rate of up to 8.1% in the first year following implantation. Despite these alarming numbers, Stryker continued to market the ABGII hip stems until April of 2012 when the obvious problems associated with the ABGII could no longer be covered up. At that time, Stryker sent an Urgent Field Safety Notification to hospitals and surgeons, warning them of the risks of fretting and corrosion associated with the ABGII. The fretting and corrosion could lead to the shearing away of metal ions into the body, causing serious medical problems and hip failure. Only a short time before this Urgent Field Safety Notification was sent out, Stryker had claimed that problems with the ABGII hip device were “rare,” affecting less than 1% of implant recipients, yet three months after the notification a recall was issued.

What is Wrong with the Stryker ABGII?

The ABGII was approved under an FDA process known as the 510(k), which allows manufacturers of medical devices to skip clinical trials which would evaluate effectiveness and safety by showing the device is substantially similar to a device already on the market. The only caveat of the process is that the medical devices will gain approval on the condition that post-market surveys will be done. By this time, however, the damage may already be done. There are several serious medical risks associated with the Stryker ABGII hip device, including pain and inflammation so severe as to require revision surgery, bone dissolution, premature tissue death, the formation of pseudo-tumors and symptoms of metal toxicity such as: Gastrointestinal, renal, thyroid, neurological and cardiovascular problems, loss of vision and hearing, reproductive disorders, disruption of DNA, anxiety, vertigo, depression, irritability, chronic headaches and skin rashes.

What Causes Stryker ABGII Component Friction?

There are a variety of theories as to why the Stryker ABGII failed; some believe mismatched components or frictional torque were the issue, others that the powder coating may have caused additional problems. Frictional torque could certainly have been a contributor, as the design of the ABGII allows the modular neck to fit into the stem via a taper junction. While in other hip implant devices, the primary area of wear is seen as the head-neck taper junction, in the ABGII, the extra movement the components allow leads to more frictional torque and more wear on the joint.

In fact, a wear analysis concluded that the majority of the wear and load-bearing in the ABGII occurred at the neck-stem taper junction, and that as bearing diameter increases, the mechanical stress will increase as well. As the neck-stem taper junction experiences excessive wear, corrosion and metal ion shear can occur as well as the formation of pseudo-tumors. Among retrieved neck-stem tapers, at least 35% of them showed signs of excessive wear and corrosion due to the frictional torque at this junction. Despite the oxide film covering the components, the stresses on the neck-stem taper unction can abrade the oxide film, increasing the rate of corrosion.

What Will Happen to Patients Harmed by Stryker ABGII Design Problems?

When mismatched metals are used—such as the titanium stem and cobalt and chromium neck piece of the ABGII—additional frictional torque and corrosion is likely. The higher the rate of corrosion, the more likely metal ions will enter the hip tissue and bloodstream. Whether ABGII implant recipients will ever fully understand how they came to be implanted with a device they were told was totally safe is unclear. It is hoped, however, that the lawsuits pending against Stryker will allow those harmed by the ABGII to at least recover some of the financial expenses associated with their implant and potential revision surgery.