Exploring Possible Causes of Zimmer Hip Failure
Zimmer’s Durom cup is facing growing challenges in the U.S. as more people report Zimmer hip replacement problems. Yet the device continues to be sold in Europe with high rates of consumer satisfaction. Why the discrepancy between the two markets?
Zimmer hip failure rates higher in U.S.
The Zimmer Durom Cup was first approved by the FDA in 2006, but only after a three-year successful track record in Europe. By 2008, however, many U.S. patients had developed Zimmer hip replacement problems and often Zimmer hip failure, some within months of surgery. Doctors claimed the device was faulty. Zimmer implemented a temporary suspension of sales to further investigate.
Zimmer hip replacement problems blamed on surgeons
Despite numerous reports to the FDA regarding the Durom cup’s tendency to loosen and migrate, and despite the strong recommendation against the device by reputed surgeon Dr. Lawrence Dorr, Zimmer concluded after its investigation that the device was fine. They released it again with recommended additional training for American surgeons, whom they said lacked the required skill or finesse to properly implant the components.
Dr. Dorr disagreed. “I can assure you this goes beyond technique,” he wrote in a letter to the American Association of Hip and Knee Surgeons in 2008.
Differences between U.S. and European Zimmer hip implants
Other factors may partially explain Zimmer hip failure in the U.S. The coating used on the cup, for example, is different here than in any other country. Unlike other hip replacement devices, the Durom cup uses no cement, but relies on a plasma spray coating to help secure it in place. In both Europe and the U.S., the coating is made with pure titanium, which is scientifically proven to fuse to bone. The plasma spray adheres to the chrome of the cup, and has a pore-like structure that is supposed to allow bone to grow into it.
In the U.S., however, this coating is slightly thicker with a slightly different structure, adjusted to comply with FDA requirements for abrasion testing of plasma-sprayed coatings. Zimmer claims to have closely examined the coating and verified that it “met requirements,” but a University of Wisconsin study showed that in over 11 percent of patients, the fusing didn’t take place properly. “[N]o significant bone ingrowth was noted at the time of Durom revisions,” the authors wrote.
Another difference—in the U.S., the Durom cup was most often used in traditional hip replacement, while European, Indian, Korean, Australian, and Argentinian doctors use it most for the newer surgery called hip resurfacing. In a total hip replacement, the entire ball of the hip joint is removed, and the surgeon prepares the thighbone to receive a metal anchor, or stem. Once that’s in place, the prosthetic ball or cup is put on top. In hip resurfacing, however, the original ball is left in place and simply “resurfaced” or reshaped and then covered with the cap or cup.
According to the Mayo Clinic, this procedure can result in a bigger hip ball than what is typically used in total hip replacement, which may fit better and reduce risk of dislocation. This could be another reason why the Durom cup was successful in European hip resurfacing operations, but not so much in U.S. total hip replacements.
Zimmer continues to fight claims of hip failure
Though Zimmer continues to maintain their device is not defective, those experiencing Zimmer hip failure have done well in Zimmer hip lawsuits, claiming thousands in settlements for medical costs and damages.