Stryker Rejuvenate Hip Implant: What is the Real Problem?

Just this past July Stryker Orthopedics issued a voluntary recall of their Rejuvenate and ABGII hip implant systems citing a potential for fretting and corrosion at the metal neck junction. The FDA convened a panel shortly before this recall to discuss the merits of continuing to use metal-on-metal hip implants due to the high number of complications suffered from recipients. The design of the Rejuvenate was believed to overcome most issues associated with the all-metal hip implants as it allowed surgeons to custom-fit the stems and necks of the implants to the size and relative activity level of the patient.

The Rejuvenate Design

The Stryker Rejuvenate consists of a ceramic ball which fits into a plastic-lined socket. Because there was no metal-on-metal ball and socket it was believed there were no metal surfaces which could potentially rub against one another, causing metal ion debris to enter the surrounding tissue or bloodstream. The Rejuvenate is essentially a two-piece system in that the properly sized metal stem and neck connect to one another then connect to the ceramic ball. The neck is made of chromium and cobalt, just like the all-metal implants and the stem is coated with titanium. Even so, by using a ceramic ball and a plastic-lined socket, it was believed there would be no issues regarding metal ion debris.

The Problem with Trundles

What the company may not have accounted for are the trundles on either side of the neck piece of the Stryker Rejuvenate implant. Trundles are essentially “divets” which allow the neck piece to slip into the stem on one side and into the ball on the other side. In other words, the stem portion of the implant goes into the femur bone, then the stem connects to the neck by popping together via the trundles, the neck connects to the ball with trundles, then the ball fits into the acetabular cup. While there is no metal ball rubbing on a metal cup, corrosion can occur where the trundles are located. Body fluids can be trapped inside the trundles, causing corrosion which leads to chromium and cobalt spilling out of that implant joint.

The Potential for Metal Toxicity

While there would not be the same high levels of metal ions resulting from this trundle corrosion as from an all-metal implant, any level of metal in the body is too much and can lead to health risks for recipients. The trundles in the implants of those patients who are typically more active can be jostled more, leading to greater levels of cobalt and chromium ion shedding. These ions can enter the surrounding tissues or the bloodstream causing necrosis, pain, infection and metal toxicity. As the trundles have not been specifically mentioned as a potential problem in the recall by Stryker, it is unlikely physicians would even think to look at the trundle area of removed implants. 

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