The Many Stryker ABGII Defects—Including Coating—and How They Affect Implant Recipients

Stryker ABGII Coating Defects

While many theories of specific design defects abound regarding the Stryker ABGII hip implant device which was recalled in July, 2012, several have come to the forefront. When Stryker recalled the implant, the manufacturer cited the risk of fretting and corrosion, leading to an excess amount of ion debris generation and failure of the hip implant. Stryker offered few clues as to how the design of the ABGII contributed to the excess levels of corrosion and the higher-than-normal failure rate of the device. One theory revolves around the fact that Stryker used a titanium stem paired with a cobalt and chromium neck component piece. The two join together with a taper junction. Much research was available which clearly showed that using mismatched components results in a higher rate of corrosion, although scientists are not clear exactly why this is true.

The excess corrosion could be due to the much harder cobalt and chromium metals as compared to the softer titanium metal. To help alleviate this problem, Stryker sprayed the implant with a proprietary mix of alloys known as TMZF, however the spray did not offer the protection expected. A second theory is that the neck-stem taper junction is a source of considerable frictional torque. Other hip implants have a one-piece, tight-cast neck-stem component, but in the interest of allowing greater range of motion for recipients, Stryker used a new design which offered a variety of stems and necks in different lengths and angles. While surgeons were now able to fit the hip implant precisely to the patient, this taper junction had turned into a source of frictional torque, resulting in further corrosion, fretting and metal ion release.

Finally, the stem of the ABGII was coated with a hydroxyapatite porous coating in the interests of encouraging the growth of bone around implant. While the HA coating of the ABGII is shallower and smoother than that used on the also-recalled Stryker Rejuvenate, the coating may have still caused additional problems for recipients. The HA coating mimics the chemical makeup of calcium and other minerals found naturally in the human body, however the coating may seep into the bone tissue. This can put recipients of the ABGII hip implant at risk of osteolysis, or weakening of the bone. When the hip bone weakens, the implant may loosen, causing chronic pain and a loss of range-of-motion. The loosening hip stem can also create popping, cracking or squeaking noises, which can signal bone loss. Further, should revision surgery become necessary, the HA coating can make the ABGII much more difficult to remove.

What Stryker ABGII Design Problems Led to the Recall?

Whether the design problems listed above were responsible for the Stryker ABGII recall or there were other issues unknown at this time, many wonder whether Stryker was aware of the design problems at the time marketing of the device began. Because the ABGII gained FDA approval through the 510(k) process, there was no requirement of clinical trials, and little safety testing was done. The process only requires that the device be substantially similar to a device already on the market and that the manufacturer follow up with post-market data. Unfortunately, by the time post-market data is gathered, many consumers may have already suffered irreversible harm.

Patients Want to Know What is Wrong With the Stryker ABGII

When metal ions enter the body after corrosion and fretting take place, they may either enter the bloodstream or lodge in the hip tissues. When the metal shards enter the tissue, there may be degradation of bone and tissue, inflammation, infection and chronic pain for the patient. As the inflammation increases, the bone and tissue may undergo total death or destruction, causing the implant to fail completely. Should this occur, revision surgery will be required. Unfortunately, ABGII revision surgery can be much riskier and more expensive than the original surgery, requiring a recovery period of up to six weeks. When the metal ions enter the bloodstream, there are a variety of adverse health issues which can result including:

·         Gastrointestinal disorders

·         Reproductive disorders

·         The development of pseudo-tumors

·         Disruption of DNA

·         Cardiovascular problems

·         Neurological issues

·         The loss or diminishment of vision and hearing

·         Vertigo

·         Anxiety, depression, irritability

·         Chronic headaches

·         Skin rashes

·         Renal and thyroid problems

Stryker has declined to comment on the actual failure rate of the ABGII, however independent studies have placed that number as high as 40%. This means that even for the patients who have not yet experienced health problems due to their ABGII implant, the likelihood that they will, is high. As the lawsuits continue to mount, it is possible that more information may come to light as far as what design defects were present in the ABGII, and how much Stryker knew as they continued to sell the implants to an unsuspecting public.

While the ABGII is not considered a “true” metal-on-metal implant due to the use of a ceramic ball, the issues patients are experiencing are nearly identical to those experienced by recipients of all-metal implants. The levels of ABGII corrosion are extremely high, both at the neck-stem taper junction and under the small metal trunnions located on either end of the neck piece. All of these design defects will become legal issues, however for patients who are suffering severe, adverse health issues due to their ABGII hip implant, there may be little consolation in finally learning why the ABGII failed.