BONEZONE:So, how does someone use Pareto Analysis, in this case?
McCloy: Pareto Analysis allows us to focus on addressing the real problem, saving time and money. The first step is to construct a bar chart and capture all of the cases and reasons for defect. Was there a design flaw? Was improper material used? Was the implant or device poorly manufactured? Was it improperly installed? Did the anchoring screws fail? Or, was it a matter of a noncompliant patient who may have been overweight or had other issues?
This provides a look at the frequency and importance of failure. So, for example, while we might be tempted to redesign bone screws, Pareto Analysis allows us to understand and address the most significant areas. With an artificial hip, it may be that metal fatigue was not the most common defect, but was the most significant. The manufacturer could then concentrate on investigating why this was happening. Were design modifications needed? Were there better material choices, or did the plastic liner separating the femoral head and acetabular component fail? Frequency and importance don’t always go hand-in-hand. Remember, the most common problems aren’t always the most important ones; a weighted Pareto Chart emphasizes the most important factors.
BONEZONE: Why is a Pareto Chart useful?
McCloy: A Pareto Chart is basically a way to capture and document all reasons for defect. Usually represented as a bar chart, it is a simple yet effective way of organizing information in this manner to help visualize the 20% most critical factors. While it’s important to employ this type of thinking early in the quality improvement initiative, a Pareto Chart is useful throughout the entire lifecycle of a product. Constructing a chart isn’t difficult. It’s just a matter of collecting and organizing data. Of course, software automates the process, today.
BONEZONE: Can you give us an example of a Pareto Chart in action?
McCloy: Say you have had problems with a bone screw that has a history of breaking. We’ll construct a Pareto Chart to look at all of the cases and reasons for defect. I’ll use my previous examples: Was there a design flaw? Was improper material used? Were the screws poorly manufactured? Was it over-torqued or otherwise improperly installed? Or was it a matter of a noncompliant patient who may have been overweight or had bone issues?
This allows manufacturers to take a look at the frequency and importance of failure. But frequency and importance don’t always go hand-in-hand. So, while we might see that the most common reason for screw failure can be attributed to postoperative infection or failure to employ stress analysis in the design stage, Pareto Analysis allows us to prioritize efforts on the most important and costly issues; in this case, material choice and design. (See Exhibits 1 and 2.)
BONEZONE: Circling back to your prior comments, how does this apply to validation and product development?
McCloy: Product development is a continuous decision-making process. Trade-offs are made along the way to balance cost, manufacturability and quality. The idea is that the product is not over- or under-designed. For example, is it required that we construct the implant from titanium, or will a less-costly material allow us to meet quality and cost targets? Pareto Analysis allows us to assign weights to the severity of failures. In this scenario, Pareto Analysis allows us to quantifiably measure the ramifications if the device fails as a result of not using titanium.
BONEZONE: What steps should engineers take when validating devices, using this method?
McCloy: Experience is the key—there’s no substitute for it. It’s also a good idea to have tests conducted by a disinterested third party; therefore, it’s often best to subcontract to an accredited, independent test lab.
BONEZONE: Many of our readers handle a portion of testing inhouse. In your experience, is there a mistake or a cautionary tale that you can provide to device companies when handling Pareto Analysis on their own?
McCloy: Pareto Analysis works best when not subjected to outside influences. In other words, one must enter into it objectively, allowing the data to speak for itself. Don’t allow preconceived conclusions or internal politics to corrupt the findings. I’ve said it before and I cannot emphasize it enough—the most frequent failures aren’t always the most important ones. This is why I recommend outsourcing to a disinterested third-party test lab.
BONEZONE: Why is this a smart tool to use?
McCloy: Earlier, we discussed verification and validation. Pareto Analysis provides internal and external agreement that a selected implant or device will meet internal and external requirements. Displaying data on a Pareto Chart will help build consensus while allowing manufacturers to concentrate resources, time and money to address the most significant issues.
BONEZONE: Are there instances where Pareto Analysis isn’t the best option?
McCloy: Yes; as I mentioned earlier, experience is absolutely critical. If a company has no experience in this area, it’s best to go another route. In cases where product history is available, it’s a good idea to leverage that data.
BONEZONE: So what’s the better option: failure analysis or Pareto Analysis?
McCloy: All testing is important, and it’s important to note that failure analysis and Pareto Analysis aren’t mutually exclusive. As with anything, the more information one has, the better are the decisions that can be made. Much like a detective inspecting a crime scene, failure analysis analyzes explants (failed implants) to determine exactly why the implant failed. Although the process takes place after the fact, information is fed back to the medical community, allowing the necessary design, material, manufacturing or installation changes to be made. Pareto Analysis, on the other hand, allows us to understand long-term ramifications of design and material decisions to optimize designs and avoid problems down the road. In my mind, each has its place in helping to ensure better, longer-lasting medical implants and devices.
John McCloy is Founder and President of Engineered Assurance, LLC. Mr. McCloy is the past owner of Accutek Testing Laboratory, which was a mechanical and metallurgical testing laboratory for clients from the medical, aerospace and defense industry. Over 12 years, Mr. McCloy built the lab to more than 50 employees. He has since retired to part-time consulting.
Engineered Assurance, LLC