Stryker’s Rejuvenate hip implant was recalled in July 2012 along with the ABGII. At the time of the Stryker Rejuvenate recall, the company stated a heightened risk of fretting and corrosion, leading to the release of metal ions into surrounding hip tissue and the bloodstream. The Rejuvenate received FDA approval in June, 2008, under the controversial 510(k) process whereby a medical device is approved because it is substantially equivalent to a device already approved. The Rejuvenate received its FDA approval based on similarity to the Wright Medical Technology Pro-femur total hip modular neck system.
Rejuvenate Based on Problematic Wright Pro-femur
Unfortunately, the Pro-femur has had more than its share of problems; although a recall was never issued, a significant number of patients with a Pro-femur implant have suffered total implant failure. The Pro-femur was marketed as being more durable, suitable for those with an active lifestyle however injury lawsuits filed against Wright Medical state that in 2000, when the implant was first marketed, Wright was aware that the titanium components presented an unreasonably high risk of fracture and failure. The Wright Pro-femur is also subject to fretting and corrosion, and has a failure rate of almost 12%. In other words, the defective Stryker Rejuvenate gained approval based on the problematic Wright Pro-femur.
What is the Problem with Dual Modularity?
Many believe the real defect in the Stryker Rejuvenate lies in its dual modularity design. Modularity refers to the components being available in sections or parts rather than one single piece. Historically hip implants were constructed in two pieces; one inserted into the natural hip socket, the other into the femur. While this type of implant worked fairly well, there were some issues; the first being that this “stock” implants did not fit every body type. Additionally, once the surgeon cemented the socket in, there was practically no way to salvage the implant if the orientation was not correct. Modular components radically changed these issues. The surgeon could now fit the hip implant to the individual patient’s size and activity level by choosing the size and length of the ball, the length of the stem section, the shape and size of the upper end of the femoral component and even the degree of offset and rotation.
The Problems with Dual Modularity and Morse Tapers
Stryker hyped this dual modularity as giving surgeons the ability to custom fit their device to the individual patient. Patients were led to believe that the metal-on-metal safety issues were a result of a poor fit—something the dual modularity of the Rejvuenate would put an end to. But the design of the recalled Rejuvenate greatly exacerbates the possibility of dissociation between the neck and body, increasing metal debris.
In fact, studies on dual-modular components point to corrosion as a primary concern in the malfunction of the Rejuvenate; this includes crevice corrosion, fretting corrosion and galvanic corrosion. In order for the dual-modularity technology to work correctly, a good junction or taper must be used at both modularity points. Unfortunately, the dimensions of Morse tapers are not standardized creating the risk of dislocation and the Morse taper connects two different materials, leading to a higher risk of fretting and corrosion. If you have a recalled Rejuvenate hip implant you should speak with your physician regarding the risks of the implant.