Tuesday, November 20, 2012

What is the Real Problem with the Stryker Rejuvenate Hip?

Although Stryker Orthopedics recalled their Rejuvenate hip implant this past July—ostensibly due to the potential of fretting and corrosion—there may be a different reason why this particular hip implant can be risky for recipients. At the end of June, 2012, an FDA panel of orthopedic surgeons convened to discuss whether there was any reason at all to continue using metal-on-metal hip implants. After all, patient after patient had suffered complications from these all-metal devices including metal ions in their bloodstream, chronic pain and infection, and early failure rate as well as necrosis and pseudo-tumors in the surrounding hip areas. Women and those patients who were significantly overweight appeared to have an even higher risk of these side effects from metal-on-metal hip implants.

Why the Rejuvenate was believed to be an Improvement in Hip Implant Design

The Rejuvenate received FDA approval in June 2008 while the ABGII received approval in 2009. The company was very enthusiastic about the new design which offered surgeons different sizes of stems and necks which could be custom-fitted to the size and activity level of patients, allowing younger, more active patients to return to their active lifestyle quickly. Because the Rejuvenate had a ceramic ball which fit into a socket with a plastic liner, the theory was that with no metal surfaces to rub against one another there should be no issues with metal debris. The modular design of the Rejuvenate and ABGII consists of a two-piece system; the metal stem and metal neck attach then connect to the ceramic ball.

The Design of the Stryker Hip Implant

The neck of the Stryker hip implant is made of chromium and cobalt just like the recalled metal-on-metal hip implants and the stem is coated with titanium. Despite the fact that the ball is ceramic, the Stryker hip has a metal-on-metal intersection which does the exact same thing as the all-metal hip implants: the metal debris which results from the metal pieces rubbing against one another can cause significant health risks. The company’s “Urgent Safety Alert” which went out to hospitals and surgeons across the nation warned that metal ion debris could be generated by “fretting and/or corrosion at or about the modular neck junction.” While this new generation of hip implants was originally thought to last at least fifteen years, the Rejuvenate and ABGII began showing signs of failure within just a few months following the first implants.

The Problem with Trunnions

There are currently over sixty adverse event reports from Stryker’s recalled hip implants however new information regarding the hip implants puts a different spin on what the actual problem with these implant systems may be. The problem may not be in the modular neck junction, rather in the “trunnions” which are on either side of the neck piece. Trunnions are like divets with the neck piece slipping down into them. This means that you have the stem of the Rejuvenate which goes down into the femur, then that stem connects to the neck, the neck connects to a ball, and the ball fits into the acetabular cup. On either side of the neck are the trunnions which allow the neck to “pop” right into the stem on one side and into the ball on the other side.

Corrosion in the Trunnions

Where these trunnions are located is where the corrosion actually occurs. Fluids from the body can get trapped inside the trunnions, causing corrosion—causing chromium and cobalt to spill out of that joint. These trunnions are small, therefore the level of metal surfaces scraping against one another is not nearly as large as in the all-metal implants. Nonetheless, when a doctor tests a patient for levels of cobalt and chromium, there could be significant amounts coming from the trunnions on the Stryker Rejuvenate.

Any Level of Metal in the Body is Too Much

This is one instance where any amount is too much. Even though it is a relatively small, finite area, any level of metal ions entering the surrounding tissue or the bloodstream can be enough to cause significant health problems for the patient. Particularly when patients walk or engage in higher activity levels, the trunnions will naturally be jostled more, leading to cobalt and chromium ion shedding which in turn leads to necrosis, pain and infection. Since it does not appear that these trunnions were mentioned by Stryker as any sort of potential risk, it is unlikely that physicians would have been looking closely at them during revision surgeries when the Stryker implants had to be removed.

Author: Sullo & Sullo Attorneys

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