When Medical Implants Fail: A Forensic Engineer’s View

portrait photo of Richard

Richard T. Edwards, P.E.

When a medical implant works as intended, it can be life-changing. A hip that allows someone to walk pain-free again. A shoulder that lets them lift a grandchild. But when an implant fails, the story changes to pain, repeat surgeries, and sometimes years spent in a courtroom. That’s where failure analysis enters the picture—uncovering not just what went wrong, but why.

Medical implants are remarkable devices, but they are not infallible. A failure can stem from a flaw in the material, a weakness in the design, or even a small misstep during installation. Tracing those causes is rarely simple, and it often requires a detailed investigation.

That’s where my work comes in. I’ve spent decades analyzing material failures in everything from industrial plants to medical devices. And because I also live with two artificial hips and a shoulder implant, I approach these cases with a dual perspective: I know what these devices should do for a patient, and I know what it looks like when they don’t. 

The Nature of the Failure Has Changed

Earlier generations of hip implants often failed because of fractured metal components. Today, failures are more likely to involve polymers—particularly ultra-high-molecular-weight crosslinked polyethylene (UHMWPE) liners—and the mechanical systems used to hold everything together.

We still get the occasional metal-on-metal case, but many of today’s implant failures fall into a few categories:

  • Worn or deformed liners – Creep and wear of polymer components can lead to instability.
  • Locking mechanism issues – Tabs shear off, liners rotate, or components separate.
  • Corrosion and metal wear – This phenomenon still happens, especially in modular systems or when fretting occurs between components.
  • Installation problems – Sometimes the issue isn’t the material, it’s how the implant was placed.  Operations are often videotaped in today’s environment, and this can be very helpful.

It Takes More Than a Microscope

When a medical implant fails and a lawsuit follows, people often seek quick answers. 

“Was it a bad part?” “Was it the surgeon?” 

But the truth is, you can’t answer that by eyeballing a broken piece of plastic or reading a surgical note. You need evidence, and you need the right tools to find it.

To separate assumptions from facts, failure analysis relies on testing and hard evidence. We use the scientific method: form hypotheses, test them, and see if the evidence supports one or more hypotheses over the others. It’s not enough to say, “This probably failed because X.” It should be shown and explained.

Depending on the case, we might run:

  • Microscopy (optical and scanning electron) to look at fracture surfaces.
  • Infrared spectroscopy and/or scanning calorimetry to assess the chemical makeup and thermal history of a polymer.
  • Hardness testing to check if the plastic has aged or changed under stress.
  • Dimensional analysis to see if parts are out of design tolerance.
  • Wear mapping or debris analysis to understand the pattern of use.

In cases that end up in court, it’s not enough to just have an opinion. Opinions and conclusions have to stand up to what’s called a Daubert challenge—a legal test of whether expert testimony is based on reliable science. 

Put simply, it’s the opposing lawyer’s way of asking, “Did you actually prove this, or are you just guessing?” Multiple theories have to be formulated, tested, and evaluated against physical and chemical evidence.

Real-World Lessons

Consider two examples that highlight just how different failure causes can look. 

A hip implant with a polyethylene liner rotated out of position. The locking tabs that were supposed to keep it in place had sheared off.  Medical polyethylene sometimes uses Vitamin E as a plasticizer.  The plasticizer can reduce the shear strength of the plastic.

Another case wasn’t about materials at all. The liner had rotated because it had never been fully locked in during surgery.  Nothing wrong with the parts—just a missed step in the operating room.  As engineers, we cannot testify to medical matters, but we can identify problems and our clients can direct those issues to the medical expert.

These experiences reinforce a guiding principle: Never assume.  Every failure investigation must let the evidence tell the story.  Evidence doesn’t lie, it may mislead but, more often, it can be misinterpreted.

A Personal Reminder

I’ve seen medical device failures from every angle: as an engineer, consultant, and as a patient. I’ve also hiked the John Muir Trail—a 211-mile trek through California’s Sierra Nevada mountains, with a hip implant—so I know what success looks like. But I’ve had setbacks too. And that’s why I take these cases seriously.

For the patient, a medical implant failure isn’t a data point. It’s their life. 

For the companies and clinicians involved, it can mean lawsuits, costs, and reputation. 

For me, it’s a matter of figuring out what really happened—and making sure the science stands up to scrutiny.

 

About the Author

Richard T. Edwards, P.E. is a consulting engineer with our Birmingham Office. He has provided consultation in the analysis and selection of materials, analysis of fractures, metallurgical analysis, materials processing, and evaluation of industrial processes toward resolution of industrial failures and accidents. You may contact Richard for your failure analysis needs at redwards@edtengineers.com or (205) 838-1040.

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