Did Frictional Torque Cause Stryker Rejuvenate Fretting?

The Stryker Rejuvenate hipimplant was approved by the FDA in 2008, yet only a few short years later, the manufacturer recalled the device, citing a higher-than-normal rate of failure and fretting and corrosion leading to metal ion debris. Those who were implanted with a recalled Rejuvenate are likely wondering just what is wrong with the Stryker Rejuvenate. These implant recipients are victims of a system which did not require clinical trials or extensive safety testing prior to marketing the hip device. Further, when the recall was issued in July, 2012, many recipients may not have even been notified of the recall, or, if they were notified, may not have fully understood what fretting and corrosion meant for their health.

Stryker Rejuvenate Defects and Design

The Rejuvenate was believed to be a truly innovative design following several dismal results from all-metal hip implants implementing a metal ball. The Rejuvenate used a ceramic ball, and offered a variety of lengths and angles in the stem and neck component pieces. This allowed surgeons to fit the implant device more precisely to the individual patient, according to the patient’s body type and size and level of activity. Because frictional torque had been a problem in the all-metal implants, primarily at head-neck junction, it was believed that the ceramic ball used in the Rejuvenate solved that problem. Unfortunately, this belief turned out not to be true.

The Rejuvenate began showing considerable wear at the neck-stem taper junction, causing metal ions to shear away and flood the body. Additionally, four small metal trunnions, located on either end of the neck piece were also sites where corrosion was present, due to body fluids being trapped beneath the trundles. Many of those implanted with a Rejuvenate began having serious health issues soon after, and the FDA received a number of adverse reports from victims of the device. Surgeons also sent information to the FDA regarding implants they had removed from their patients which appeared to have some sort of “black rust” on them. As more and more patients relayed health problems to their doctors and surgeons, and more surgeons noted health issues among their Rejuvenate patients, questions began being asked regarding the safety of the implant.

The FDA and the Rejuvenate

Although the Rejuvenate was approved by the FDA, that approval process fell under the 510(k) program, which has increasingly come under scrutiny. This particular program allows medical devices to gain approval based on their similarity to a device already on the market. In the case of the Rejuvenate, the titanium stem is really the only similarity between the implant the Rejuvenate claimed to be substantially similar to—the Wright Profemur.  As with many other devices approved under this process, the Wright Profemur has had problems of its own, and the device the Profemur was considered to be substantially similar to, also experienced problems.

Was Stryker Aware of Safety Issues Related to the Rejuvenate?

Recipients of the Rejuvenate may wonder whether the company knew there were Stryker Rejuvenate design problems prior to its release, and whether consumer safety was sacrificed in order to put more profit into Stryker’s coffers.  Although those questions may never be fully answered, many believe Stryker definitely downplayed the potential risks of the Rejuvenate up until they had little choice but to issue a recall. The specific health issues seen in those with a Rejuvenate hip implant were metallosis and metal toxicity. When the metal ions which shear away from the implant lodge in surrounding tissues the following can occur:

·         Infection

·         Severe inflammation

·         Chronic and severe pain

·         Bone deterioration and loss

·         Tissue deterioration and death

When the metal ions find their way into the patient’s bloodstream, metal toxicity, including one or more of the following symptoms can occur:

·         Gastrointestinal disorders

·         Alterations in DNA

·         The development of pseudo-tumors

·         Neurological and cardiovascular disorders

·         Irritability, depression and anxiety

·         Vertigo

·         Memory loss

·         Chronic and severe headaches

·         Reproductive disorders

·         Loss of hearing and vision

·         The development of certain types of cancer

Although Stryker stated fretting and corrosion at the time of the recall, there was little information of the causes of that fretting and corrosion. Among the design defect theories of the Stryker Rejuvenate, mismatched components, the powder coating and frictional torque are considered likely suspects. Mismatched components relates to the titanium stem Stryker paired with the much-harder cobalt and chromium stem. Scientists believe the harder cobalt and chromium reacts negatively with the titanium, causing an excess amount of metal ions.

Stryker Rejuvenate Component Friction

Because frictional torque had previously been seen primarily in the head-neck taper portion of metal implants, it was not expected in the neck-stem taper of the Rejuvenate. The taper portion of the components allows them to lock together securely, and when implanting a Rejuvenate, the Morse taper of the neck is pounded into the stem (also responsible for the release of metal ions). Scientists believe the lever-arm effect of the Stryker neck taper is responsible for increased movement at the neck-stem junction and this particular junction is considered to be eccentrically loaded. 

In other hip implants which are constructed of one tight-cast piece, there is little to no movement at the neck-stem area, however the Stryker Rejuvenate allows for additional movement, creating frictional torque where the two components come together. Among Rejuvenate recipients who are particularly active, the frictional torque is much higher, leading to excess wear on the joint. The formation of pseudo-tumors may also be related to the excessive wear at the neck-stem taper junction. Once pseudo-tumors form, they must be surgically removed, even though they are not usually cancerous. It is likely that as time goes on and more lawsuits are filed, more facts will come out regarding the safety issues surrounding the recalled Stryker Rejuvenate.