In what has become an alarming trend in drug and medical device manufacturing, Smith and Nephew felt compelled to copycat other hip implant manufacturers and market a pair of dual modular hip stems. This trend is alarming because it is yet another example of marketing and fierce competition in the orthopedic manufacturing community driving the innovation bus as opposed to trying to meet a true need. Companies continue to dream up reasons why new products are necessary and then when the products fail, hide behind claims the market demanded them. This behavior consistently gets companies in big trouble, frequently at the expense of injured consumers. The drug and medical device industries are addicted to innovation for innovation’s sake.
The Story Starts With Cremascoli
In this instance, Wright Medical Inc. purchased older technology from an Italian company named Cremascoli. In 1987, Patrizio Cremascoli patented one of the first dual modular femoral stems. Dual modularity refers to the femoral stem being manufactured in two pieces as opposed to one. Dual modular stems have a separate femoral neck component that is inserted into the stem. Traditionally, the femoral stem and neck were, and continue today, to be one piece. Dual modularity was supposed to, in theory, provide surgeons with the ability to more closely reproduce the patient’s native anatomy by supplying different, interchangeable neck options of varying lengths and offsets. This was supposed to improve device performance and patient outcomes. Despite the fact the Cremascoli design met mixed reviews in Europe, Wright purchased the technology and in 2002 introduced its Profemur Z in the United States. It was the first dual modular femoral stem in the U.S. domestic market.
As is par for the course, Zimmer, Stryker and Smith and Nephew all quickly jumped on the band wagon and began developing a copycat dual modular stem. This despite the fact reports began circulating that Wright’s Profemur was prone to neck fracture. Of course, if another company offered a product they didn’t, they would lose precious market share. By 2008, both Stryker and Smith and Nephew had obtained regulatory clearance to market dual modular stems. In Stryker’s case, the Rejuvenate and ABG II were developed and sold. The SMF and Redapt stems were Smith and Nephew’s version of the dual modular stem.
A Material Difference
Unlike Wright Medical, and likely due to reported stem fractures, Stryker and Smith and Nephew manufactured their modular necks out of chromium/cobalt allow where Wright had used titanium. Chrome/cobalt alloys are much stronger than titanium. However, in doing so, both companies ignored years of reported medical literature about the use of mixed metals at critical interfaces between component parts. Since the neck inserts into the stem and obtains fixation through a press-fit Morse taper junction, the mixed metals contact one another at a point of intense stress. Micromotion between the two components is inevitable. With motion comes fretting and with fretting comes corrosion. When corrosion takes place, toxic metal wear byproducts are released into the surrounding tissue. All this was well known and contained in the published literature.
Not surprisingly, by 2012 in Stryker’s case and 2016 in Smith and Nephew’s, their dual modular hips had failed at such alarmingly high rates the companies issued voluntary recalls of the Rejuvenate, ABGII, SMF and Redapt stems. In both instances, patients were being forced to undergo premature, unnecessary revision surgery due to metal wear toxicity.
The irony of the entire dual modular story is the publication of several medical studies concluding after extensive study that dual modular technology does not improve implant performance or patient outcome over traditional one-piece stems. What a shock. The widespread adoption of technology that was never needed in the first place. Will it ever end?
In some sense, justice has been served. Both Stryker and Wright have collectively paid several billion dollars in settlements and judgments because they marketed these devices. Along the way, thousands of victims suffered and continue to suffer disability due to these devices.
The moral of this story is that existing hip implant designs are robust and mature. There are, and have been, perfectly acceptable, well performing devices available for many years. Beware innovation and steer clear of any hip implant design or device that is marketed as being the next greatest thing. Ask your physician questions. Find out what he or she intends to put in your body. Having now represented well over a thousand hip implant patients, my advice is to find a competent surgeon who intends to implant a one-piece titanium stem, ceramic head, highly crosslinked polyethylene liner and one-piece titanium acetabular shell. That is your best bet for a pain free, mobile, happy outcome.