Posted on 08/23/2022 at 03:20 PM by Katie Zakutansky

medical device failure analysis

Humans and bikes are more alike than we think. Both require proper maintenance for optimal performance. Both roll with the flow and sometimes require repairs after accidents, prolonged use, or misuse. Imaging, plates, screws, fixtures, and space fillers are some of the tools used to fix both humans and bikes. However, there are many factors that can lead to a failure in a body or bike, and to repair them effectively, we need to understand the cause. To understand the story behind a failure requires the right tools, such as cameras and microscopes, and the right scientific knowledge.

Imaging

Just as other engineers may examine material fracture patterns from a bike or part to analyze a product failure, biomechanical engineers will examine loading conditions, fracture patterns, and injuries to analyze the cause of an anatomical or medical device failure. From the parts, pieces, and other evidence, they work to extract a scientifically based narrative of what happened and why. For example, a CT scan can be utilized for both bikes and bodies. When a bike part breaks, engineers examine the fracture or product failure macroscopically and microscopically. The same is true when someone's femur breaks or joint implant begins to squeak. Biomechanists examine the available evidence, such as loading conditions, implant, skeletal radiology images, and medical records to develop a well-rounded understanding of what the body is telling us.

medical CT scan

The CT scan above was performed in-house at ESi, and demonstrates one of the ways we might examine the delamination of carbon layers within a fractured bicycle component. Whether we are scanning bikes or bodies, we work to identify and map internal structures and better understand what a fracture is telling us.  

Plates

After orthopedic trauma, bone plates may be used to immobilize broken bone segments for proper healing. We can compare bone plates to the welds of a bike frame. Bone plates come in different shapes with angles and geometries designed for specific uses. Similarly, there are different bicycle frame geometries for specific riding styles or cycling needs. Just as plates can be used to hold broken bone pieces together, welds join different tubes of a bike frame together. However, unlike welds on a bike frame, doctors must use surgical screws to hold bone plates in place. When a failure occurs on a bike or in a body, it often takes expertise in different areas and disciplines to thoroughly analyze the evidence; depending on the type of failure, you may need a biomechanical engineer, mechanical engineer, metallurgist, medical professional, or others with specialized expertise.

Screws

On a bike, screws can be used to keep clamps tight, bottle cages in place, or brakes and derailleurs working just right. Screws can also be placed in a body for similar purposes. Orthopedic screws are designed with varying threads and specific bone(s) in mind. A cortical screw typically has fine threads along the full length of a screw, while a cancellous screw has coarse threads present only at the tip of the screw. A cannulated screw has a hollow shaft that allows for concurrent use of other fixation devices. Bone screws are used to keep bone fragments, bone plates, implants, or tissue in place, and with proper positioning, can keep your body moving just right. Most bike riders know when their derailleur isn’t adjusted correctly. Common signs may be poor shifting, a rubbing chain, or dropping a chain altogether. On the other hand, the physical pain of a misaligned or misplaced bone screw may be harder to diagnose. When a screw fails, an in-house metallurgist or material scientist may be needed to examine fracture or shearing patterns. 

External Fixators

During construction, a weld fixture holds the bike frame pieces in place as they are welded together. Similarly, if a patient sustains a severe fracture and cannot immediately undergo the necessary surgery, an external fixator may help provide temporary stability. These medical devices are specifically designed for areas the may require additional stability, such as an open fracture where the surrounding area has significant soft tissue damage, or a halo-vest which is used to protect a patient’s neck or cervical spine after an accident. When riding a bike, it's especially important to wear a helmet and Protect Your Noggin!

Bone Cement

If you’re a speed racer and have a carbon fiber bike frame, you may be thinking... but my bike doesn’t have any welds. In that case, speed racer friend, the pieces of your frame are strongly held together with an epoxy resin. In some ways, bone cement can be thought of as an orthopedic version of this resin, but is instead used to create a tight fit for an implant. It holds the bone and implant tightly together like the resin holds the pieces of the carbon fiber frame together. 
Bicycles, bodies, and medical devices seem worlds apart. But when it comes to failures and fixes, both require specialized knowledge and equipment, coming together to build a contextual, detailed understanding of what happened and why. At ESi, we use a team-oriented approach that brings together broad multidisciplinary expertise and advanced equipment capabilities to shed light on the reason for complex failures. Then, armed with this knowledge, we work with our clients to identify appropriate measures to resolve the issue and reduce the risk of it happening again.