Thursday, November 28, 2013

Stryker Rejuvenate Design Defect Theories: Coating

The Stryker Rejuvenate hip implant was recalled by Stryker in July, 2012 after numerous reports came in to the FDA regarding symptoms of metal toxicity and metallosis among recipients. Stryker cited a higher-than-normal rate of failure due to the likelihood of fretting and corrosion, leading to excess metal ion debris generation. The design of the Stryker Rejuvenate was considered extremely innovative at the time it was released. After many recipients of all-metal hip implant devices suffered significant health problems, the ceramic ball of the Rejuvenate was believed to be a safer alternative with fewer risks of metal ion shear.

 

Specific Stryker Rejuvenate Design Problems

The Rejuvenate also offered surgeons a wide variety of options as far as fitting the metal implant more precisely to the individual patient. The Rejuvenate, with its array of neck and stem components of different sizes and angle, allowed surgeons to take into consideration the patient’s size, body type and level of activity when implanting the device. The marketing of the Rejuvenate was aimed specifically at younger, more active patients, and over 9,000 of the devices were quickly sold and implanted within the few years between FDA approval in 2008 and the recall of the Rejuvenate in 2012.

 

Stryker and the FDA

Consumers who had the Rejuvenate hip device implanted in their body as well as the surgeons who implanted the devices obviously believed the design of the hip implant was safe. These consumers certainly never expected they might have to deal with serious health issues such as metallosis and metal poisoning when they agreed to have a Rejuvenate implanted in their body. While the FDA did approve the Rejuvenate, that approval came under a controversial program known as the 510(k) process. This process allows manufacturers to skip clinical trials and conduct very little safety testing so long as they can show the device is substantially similar to another device already on the market.

 

What is Wrong with the Stryker Rejuvenate?

The Rejuvenate application was based on the Wright Profemur, although the two devices have very little in common other than a titanium stem. The Profemur has experienced certain problems of its own and the Profemur gained FDA approval based on yet another hip implant device. Whether the process currently in place by the FDA bears any responsibility for the many patients harmed by the Rejuvenate is debatable, however many believe Stryker was well aware of at least some of the issues surrounding the Rejuvenate from the beginning. Within the first two years the Rejuvenate was marketed, the FDA received numerous adverse reports from patients experiencing difficulty with the device as well as from surgeons whose patients were reporting adverse health effects. One surgeon even noted that when he removed a Rejuvenate from a patient, there were significant amounts of what looked like “black rust” on the device.

 

Symptoms of Metallosis and Metal Toxicity

The corrosion which can occur in Rejuvenate implants was unexpected in that most metal hip implants show the majority of wear at the head-neck joint, while the Rejuvenate shows the most significant wear at the neck-stem taper joint. This excessive wear is responsible for the release of metal ions into the body, leading to symptoms of metallosis and metal toxicity. Metallosis symptoms due to metal ion shards lodging in hip tissue include inflammation, infection, chronic pain for the recipient and the degradation of tissue and bone. Symptoms of metal toxicity can occur when the metal ions enter the bloodstream. Some of the most reported symptoms include: cardiovascular and neurological disorders, loss of vision and hearing, vertigo, chronic headaches, reproductive disorders, renal and thyroid problems, irritability, depression, anxiety, the development of pseudo-tumors and even DNA disruption.

 

When the levels of cobalt and chromium reach dangerous levels—or when they have caused significant symptoms in those patients who are especially sensitive to metals—the implant will likely require removal, known as revision surgery. Because the stem of the Rejuvenate is placed so deeply within the femur, it can be extremely difficult to remove. While Stryker has remained largely silent regarding the specific design defect theories of the recalled Rejuvenate, there are three primary theories. The first is mismatched components: mixing the titanium stem with the cobalt and chromium neck can result in even more metal ion debris, possibly due to the disparity in hardness between the two components. Frictional torque at the neck-stem taper is also present in the Rejuvenate.

 

Stryker Rejuvenate Coating Defects

Finally, the HA coating and the TMZF coating may have both caused additional problems for Rejuvenate patients. The stem of the Rejuvenate is coated with a proprietary titanium alloy blend, mixing titanium, molybdenum, zirconium and iron. The mixture of alloys is combined with plasma spray which, according to Stryker, would cure the issues associated with mismatched components. The TMZF coating spray was meant to prevent the harder cobalt and chromium neck piece from reacting to the softer titanium stem, making them resistant to fretting and corrosion. Unfortunately, post-market data has revealed that the TMZF coating did not perform as expected, allowing cobalt and chromium metal ions to shear away during periods of activity, entering the body and potentially causing metallosis and metal poisoning.

 

For reasons not well understood, most metal-on-metal implants release cobalt and chromium in roughly the same amounts, yet in the Rejuvenate implant, cobalt levels exceed those of chromium. Whether the TMZF coating actually caused more corrosion and chromium ions to shear away is not known, however, despite claims to the contrary, it seems likely that the coating failed to prevent those ions from releasing. The HA coating on the stem of the Rejuvenate is meant to encourage the ingrowth of bone by mimicking such naturally occurring minerals as calcium. The Rejuvenate’s HA coating is especially rough and deep—much more so than that of the ABGII—and has been found to seep into the bones, causing osteolysis, or weakening of the bone. When the bone becomes sufficiently weakened, the hip implant will likely fail. When taken as a whole, it would appear that the many claims of Stryker regarding the innovative design and safety of the Rejuvenate were simply that—claims.

 

Stryker Lawsuits and Consumer Safety

Although all the facts are not yet in, the lawsuits already filed against Stryker regarding the recalled Rejuvenate as well as those which are likely to be filed may eventually shed some light on the reasons behind the failure of the Rejuvenate. While this may be little consolation to those harmed by the hip implant, this information could prevent similar problems in the future for those receiving a new hip implant.

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