Is Dual Modularity the Real Defect of the Stryker Rejuvenate? How the Rejuvenate Recall May Affect Recipients of the Implant

This past July Stryker Orthopedics recalled two hip implant models: the Rejuvenate and the ABGII. The Rejuvenate gained FDA approval only a few short years earlier, in 2008. The approval for the Rejuvenate fell under a process known as the 510(k) which has come under fire after many devices approved under the process were found to be defective. Under this process a new medical device must only show it is substantially equivalent to a device which has already garnered FDA approval. Clinical trials are not a requirement of the 510(k), therefore many people have ended up harmed from a defective medical device approved under this process.

In fact, the Rejuvenate received FDA approval based on its similarity to the Wright Profemur modular neck device. The Pro-femur has not been recalled, however since its introduction to the market in 2000, there have been a significant number of adverse reports regarding the device as well as injury lawsuits filed against the company. Many of these lawsuits allege that Wright was aware of the problems associated with the Pro-femur including an unusually high risk of failure and fracture. Like the Rejuvenate, the Pro-femur also has a significant risk of fretting and corrosion.

Is the Stryker Rejuvenate Defective Because of the Dual Modularity?

Originally all hip implants were designed with one junction between the ball and the neck portion. Dual modularity implemented a junction between the ball and the neck as well as a junction between the neck and the stem. Stryker’s goal with the new dual modularity design was to allow surgeons to use multiple necks with various angles and lengths so a custom fit for each individual patient could be obtained.

The surgeon can choose 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 the degree of rotation and offset. While in theory the dual modularity hip implant device should provide a huge gain in performance as well as putting an end to safety issues which occurred from a poor fit. But dual modularity design also increases the likelihood of separation between the body and the neck, thus increasing the levels of metal ion debris.

When Dual Modularity Causes Corrosion

There are three types of corrosion the Rejuvenate is subject to: crevice corrosion, fretting corrosion and galvanic corrosion. When a dual modularity device such as the Stryker Rejuvenate is used, a good taper must be implemented at the modularity points. Many hip implant manufacturers use a Morse taper however due to a variety of manufacturers, the tapers are not uniform in their dimensions. Even the slightest variance can greatly increase the risk of dislocation for the patient.

The Morse taper may also connect two disparate materials which can also increase the risks of fretting and corrosion. When a ceramic femoral head is used, the Morse tapers which join the head with the shaft can produce stress within the ceramic material. These are known as hoop stresses and can lead to serious fractures of the ceramic head when products of two different manufacturers are placed together.  As you can see, the dual modularity of the Stryker Rejuvenate could well be reason for the recall.