Zimmer NexGen CR-Flex Knee: Medical Devices & the 510(k) Approval Process

The Zimmer NexGen CR-Flex Knee is an artificial knee that has been marketed and sold by Zimmer, Inc. since 2003. Like the majority of medical devices in the United States, it was approved by the FDA using the 510(k) approval process which allows manufacturers to avoid more costly clinical testing by claiming that their new products are substantially equivalent to previously approved products. In essence, manufacturers like Zimmer can piggyback on previously approved products.

You may wonder why the 510(k) process exists if it allows manufacturers to escape important testing of their products. The 510(k) process serves a valuable role in allowing manufacturers to make small incremental improvements to their products without having to go through the rigorous and expensive testing required of completely new devices. The goal is to allow for new advancements that do not affect the safety of a device to be quickly implemented.

The problem is that some products slip through the 510(k) process that clearly could have benefitted from more robust testing. While replacing one screw with a slightly different screw might not require clinical trials, many minor changes in a product might combined be the equivalent of making a major change requiring more testing. The FDA relies on companies like Zimmer to provide them all the relevant information they need to make an informed judgment about a product. If companies mislead the FDA or fail to provide an accurate depiction of their device, the FDA cannot perform its function of ensuring the public welfare.

On March 11, 2010, Doctors Richard Berger and Craig Della Valle presented evidence of the high failure rate of the Zimmer NexGen CR-Flex Knee at the American Academy of Orthopaedic Surgeons Annual Conference. Most artificial knees are implanted using cement to connect the implant to bone. Some models, like the Zimmer NexGen CR-Flex, are implanted without cement. These artificial knees rely on bone growth to firmly attach the implant. Dr. Berger found that 36% of the Zimmer NexGen CR-Flex knees in his study showed signs of being loose with 9.3% requiring revision surgery. The problem that Dr. Berger found was that the thigh bone was not growing into the NexGen CR-Flex as well as expected. Dr. Berger recommended that the Zimmer NexGen CR-Flex should not be used for any patient, although it is still commercially available.

In the end it should be manufacturers such as Zimmer that are held accountable for creating safe and effective products. No one is in a better position to evaluate a device and determine what testing needs to done than the designer and manufacturer. If companies fail to adequately design and test their product, or even worse if they mislead the government and the public regarding the products safety, the companies should be responsible for whatever damage is caused to the American people.

Categories: Medical Devices