The Stryker Rejuvenate hip recall occurred in July, 2012 after receiving FDA approval only three years prior in 2009. Since that time many adverse reports from recipients of the recalled hip implant have been sent to the FDA. Another recalled hip device, the DePuy ASR, has been found to have several design flaws which led to a variety of serious symptoms among recipients. Likewise, as time has passed since the recall of the Stryker Rejuvenate and ABGII, design flaws continue to be discovered. The “official” reason given for the Stryker recall was the increased risk of fretting and corrosion at the neck juncture of the Rejuvenate and ABGII. While this is definitely an issue, since that time several more design deficiencies have come to light.
Problems with the Rejuvenate Hip Stem
First, the Stryker recalled hip devices implement a modular femoral neck which fits into the femoral stem. The neck portion is constructed of cobalt and chromium while the stem is made from titanium. This can cause mismatched components in that several studies have shown a cobalt and chromium hip implant part attached to a titanium part can lead to problems. One 2012 study case report stated that the “trunnion mismatch between a titanium stem and a cobalt-chromium adapter sleeve led to a galvanic reaction that produced corrosion products that ultimately were detectable in the patient’s bloodstream.”
In short, it appears that dissimilar metals used in a hip implant device can lead to a generation of metal debris as well as adverse tissue responses in the patient. As far back as 2002, a study entitled A Multi-Center Retrieval Study of the Taper and Interfaces of Modular Hip Prosthesis concluded that corrosion was found to be significantly higher for mixed alloy versus similar alloy components. Moderate to severe corrosion was found in approximately 28% of similar alloy components but was found in 42% of mixed alloy components. Whether this is due to the fact that the cobalt and chromium components are harder is as yet unknown.
Frictional Torque Issues Related to the Stryker Rejuvenate
The second design flaw of the Stryker Rejuvenate and ABGII lies in the device’s frictional torque. While there is no movement in one tight-cast piece of a hip implant, the recalled Stryker hip implants are constructed of a modular neck which fits into the stem piece resulting in additional ability for movement and frictional torque where the two come together. That frictional torque leads to wear on the joint. In some cases significantly higher cobalt levels have been attributed to increased mechanical stress as the bearing diameters increase. A wear analysis of a modular neck and femoral stem showed the most wear where the neck meets the stem. This excessive wear may also be responsible for the formation of pseudo-tumors as well as the release of metal ions into the body. A 1992 study showed that 35% of retrieved head-neck tapers showed signs of moderate to severe corrosion, likely as a result of the stress and movement at the joint, or the frictional torque.
TMZF Coating Issues Can Lead to Cobalt Toxicity in Hip Replacement Patients
Finally, the TMCF coating has caused problems in Stryker’s recalled hip implants. The Stryker Rejuvenate Stem is coated with a proprietary titanium alloy blend which mixes titanium, molybdenum, zirconium and iron. These alloys are then mixed with a plasma spray. The company’s claim was that this technology “cured” the issues of mixing titanium with chromium and cobalt—the spray was supposed to circumvent the problems associated with mixing the two metals. While the company asserted this patented blend resisted corrosion and fretting, post-market data has revealed that is simply not the case. When fretting and corrosion occur, tiny metal ions of cobalt and chromium are sheared away into the body.
Cobalt Levels in Hip Replacement Recipients
In these particular recalled Stryker hip implants, it appears that more cobalt is pulled from the devices than chromium (In other metal-on-metal hip implants, the cobalt and chromium levels in the body are very similar). The potential symptoms of cobalt poisoning include: hypothyroidism, neurological and cardiovascular damage, hearing and vision loss, neuropathy, seizures, liver damage, headaches and cancer. At this point Stryker Rejuvenate hip recall lawsuits are on the rise as more and more recipients of a Rejuvenate or ABGII have begun experiencing serious side effects from the recalled implants.