New products are carefully planned, meticulously designed, and thoroughly tested. Still, no matter how diligently they are planned and tested, there will be lessons learned along the way. Customer usage data is fed back to product development process to improve future versions of the product. Generally, the changes are more evolutionary than revolutionary: with goals to incrementally improve durability, weighting, or performance. Sometimes, however, lessons are learned the hard (and expensive) way.
Few industries can identify with this scenario like the medical industry. Here product failure can literally have life and death consequences. This is why medical implant manufacturers have such rigid standards and safeguards in place to ensure quality … usually. With all of the investment in design and manufacturing technology, human error can still bring the whole thing crashing down.
A little more than a decade ago, when joint implants (such as hip replacement) were becoming widely popular, a valuable lesson was learned. As metals come in to contact with one another, through either failure or normal wear, a process known as micromotion or “fretting,” can occur. When this happened, many patients experienced the following:
- Fretting (wear) and/or corrosion at the modular-neck junction possibly leading to osteolysis (bone dissolution)
- Joint loosening/dislocation
- Excessive metal debris leading to metal ion generation
- Inflammation of tissues leading to metallosis, necrosis (death of tissues) and/or pain
- Hypersensitivity/allergic response (infections)
- Broken devices
- Adverse Local Tissue Reaction (ALTR)
All artificial hip implants carry risks including wear of the component material. Metal-on-metal (MoM) hip implants have unique risks in addition to the general risks of all hip implants. In MoM hip implants, the metal ball and the metal cup slide against each other during walking or running. Metal can also be released from other parts of the implant where two implant components connect. Metal release will cause some tiny metal particles to wear off of the device into the space around the implant. Wear and corrosion at the connection between the metal ball and taper of the stem may also occur. Some of the metal ions (e.g. cobalt and chromium) from the metal implant or from the metal particles will enter the bloodstream and are circulated throughout the body creating a significant health hazard that resulted in serious illness, astronomical insurance claims, and, of course, litigation. As the scientific and manufacturing communities continued to learn, Titanium emerged as the material of choice solving the problem – or did it?
As more than one medical implant manufacturer learned, a good product design, one that has been painstakingly tested, and the most advanced materials are no guarantee against manufacturing process breakdowns. I’ve seen cases where multiple manufacturers produce implants only to find out when it was too late that the wrong material was used. In some of these instances cold rolled steel (CR) was mistakenly used in place of titanium to manufacture spine stabilizing rods. Because of the human body’s high concentration of saline, this material would over time experience corrosion – just like a rusty nail in the rain. The structural integrity of the corroding metal rods offered no spine support. In addition, harmful chemicals were released into the body posing health risks while causing extreme irritation to surrounding tissue.
Dozens of surgeries were performed with the faulty rods. The manufacturer and had to recall the implants and surgeons had to go back in and remove the bad rods and replace with the correct ones. As you can expect, high insurance claims and lawsuits followed. The mistake nearly cost these manufacturers their business.
Positive Material Identification
Today there are methods available to help manufacturers be certain of materials being used. The process, known as Positive Material Identification, consists of tests to determine:
- Elemental Analysis: These tests determine if the materials contain the correct alloy. Wet Chemistry with Gasses is a process used to melt down a portion of the material to identify elements
- Mechanical Analysis: A micro-hardness edge-to-core test is performed to determine if the material is as strong as it should be.
- Gases: Metals contain gases. Testing for gasses is used to identify the type (nitrogen, hydrogen, oxygen) and amount of gasses within the metal. Gass content has a direct impact on material strength. Too much of a certain gas and the metal will not meet fatigue/strength standards.
Of course, if the manufacturer had checked with a simple refrigerator magnet, he would have discovered the material was positive for iron and rejected the lot (titanium is not ferro-magnetic). To learn more about Positive Material identification please contact me. I’ll be happy to offer suggestions on how you can ensure the structural integrity of your medical implants.
John McCloy has plenty more disturbing details about implants gone wrong:
- Just When I Thought I’d Seen It All…
- Be Careful Where You Sign
- Spinal Rod Failure & the Cost of Higher Education
Look out for more horror stories in the future! Find more information on Engineered Assurance here.