04242014Headline:

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Hip Implants: When Innovation Does Not Equate to Improvement

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Modular design hip replacements were first introduced about 30 years ago to allow surgeons intraoperative flexibility. They were marketed to younger patients who were presumably more active.

Although there was little data regarding the viability of such designs, that did not stop the introduction of modular hips into the marketplace and the drive to “innovate,” as the medical industry likes to call it, when they readily adopt the latest, greatest and market it as a revolutionary improvement.

Now we are finding this may not be true.

A newly published study in the Journal of Bone and Joint Surgery found 11 patients underwent early revisions after undergoing a total hip arthoplasty with the Stryker modular femoral stem design. It now appears the additional modular junction creates new opportunities for corrosion between the neck and the body of the stem.

Since most Stryker Rejuvenate implants used a ceramic ball and polyethylene socket (ceramic on plastic) both surgeons and patients felt secure in believing that the metal toxicity issues associated with metal-on-metal ball and socket designs were not present; however, the Stryker Rejuvenate did in fact have a significant metal on metal connection. The Rejuvenate design called for the neck and stem (typically one piece) to be two pieces. To assemble the device, the modular neck was inserted into the stem. Because both are made of metal, a significant metal on metal junction resulted.

To increase complications, the dual taper stems, while allowing for increased options for movement, create new areas that can potentially corrode, specifically the neck/stem junction.

The Rejuvenate combined a titanium-molybdenum-zirconium-iron (TMZF) alloy for the stem with a neck made from cobalt-chromium. In this study, it was just seven months after implant that most patients began experiencing pain. None of the patients suffered infections but serum cobalt levels were elevated in the patients’ blood. Fluids were beginning to collect in tissues and pseudotumors were seen in all but one patient.

These failures mimicked those seen in previously recalled metal on metal hips even though the articular surfaces were not metal on metal. Instead of a 15-year life expectancy for a hip replacement, revision surgery took place at 15 months. And this was difficult surgery necessitating removal of the implant along with bone and necrotic tissue. Pale green chromium phosphate particles were observed. The cause of the failure was corrosion of the femoral neck-body junction. Also the femoral head-neck junction had corrosion though to a lesser degree. When the authors inspected the tissues surrounding the defective hips microscopically, the tissue showed dead cells and a high concentration of metal.

What’s ahead for these patients, asks two very prominent New York-based surgeons? In a commentary that accompanies the published report, the doctors wonder if patient’s bodies are more susceptible to future corrosion since they have had complications.

When will the next “innovation” subject patients to new dangerous “complications”?

After all, these hips were introduced to the market using the FDA’s 510(k) notification process. To obtain clearance to sell the device, manufacturers notify the agency that the new product is “substantially equivalent” to another already on the market. But what if those already on the market are defective? That doesn’t matter it turns out- a defective and even recalled medical device can be named as a predicate device. Go figure.

Rep. Edward Markey tried to stop that from happening with the Sound Devices Act he introduced into Congress last year. The bill would have given the FDA the authority to reject medical devices if their predecessors were subject to a recall or in the process of being recalled. It would also require medical device manufacturers to explain why their products are different from earlier versions, to explain the “innovation” as it’s called.

That was defeated. In fact, the bill didn’t get even one vote in committee.

Instead why not require clinical trials to be conducted before a new orthopedic implant can be sold to consumers? Sounds like a common sense idea that injured patients assumed was already happening. They assumed wrong.