Michael Barbella, Managing Editor12.21.21
His name may not carry the notoriety of Robert Jones, Hugh Owen Thomas, or even Sir John Charnley, but Duncan Dowson is nevertheless an orthopedic icon in his own right.
The former University of Leeds professor and decorated scientist who died last year at 90 is regarded as the father of biotribology and a pioneer in formulating elastohydrodyamic theory, a foundational concept used to describe the lubrication of gears, cams and bearings. That theory forms the basis for many of the analytical tools and methods Dowson created during his 70-year career, including a film thickness formula for hip joint prostheses that emanated from his 1960s-era research on total hip arthroplasty.
Industry pundits consider Dowson’s contributions to biotribology and elastohydrodynamic theory to be essential to the evolution of joint simulation and wear.
“Innovative numerial solutions for elastohydrodynamic lubrication problems pioneered by Dowson provided further insights into the mechanism of ankle, knee, and hip synovial joint lubrication,” a June 2020 editorial in lubricants stated. “Dowson investigated total joint replacement with an UHMWPE acetabular component, cushion bearing behaviour for knee and hip arthroplasty, and lubrication of total hip replacement joints created with materials of high elastic modulus...For more than 60 years, Duncan Dowson sustained invaluable contributions towards the advancement of total joint replacement prostheses.”
One of the most invaluable—and lasting—contributions arising from Dowson’s biotribology work was the development of knee simulators, which are used to perform wear testing of knee implants. Dowson detailed such a device for the first time in his 1977 book, “Evaluation of Artificial Joints.”
Simulators for knees, hips, and other joints reproduce both the active and natural motion of their respective parts to assess the kinematics and kinetics of total joint arthroplasty. The testing simulated by these devices allow researchers, product engineers, and manufacturers to evaluate the wear performance of their implants and bearing materials under physiological conditions. Such testing helps improve designs and leads to safer joint replacements.
ODT’s feature “Testing Complete” details the trends and market forces driving orthopedic testing and analysis. Mark Escobedo, senior sales engineer at Westpak, was among the experts interviewed for the feature; his full input is provided in the following Q&A:
Michael Barbella: Please discuss the latest trends in testing methodologies for orthopedic products.
Mark Escobedo: Like all medical devices, orthopedic devices have to maintain sterility following distribution from the point of manufacture to the point of end use. Looking at that concept from a high level, that seems fairly routine. However, orthopedic devices come in a variety of different sizes to accommodate the patient. This creates a unique situation where the device can be sent back to the manufacturer. The device may then get repackaged, need to be sterilized again, and sent back out to another hospital. How do you test for that? Are there a number of cycles that make sense? We have helped clients develop their test plan to meet this need. Each company will have specific needs depending on the product type and how the product moves through the distribution environment.
Barbella: What are the most pressing challenges facing orthopedic device testers, and what kinds of solutions are available to them?
Escobedo: Our focus is primarily on the packaging that protects the product. We need to show the packaging maintains sterility. Currently, we use two test methods that are destructive to the packaging. In addition, one test method is Qualitative in nature. This can translate into a requirement for a relatively large sample size as the qualitative data collected is considered attribute data. Once we are done testing the packaging, the device is no longer sterile. Non-destructive package testing technology does exist, but it requires custom fixturing. The challenge for us would be to offer a non-destructive test that is a “one size” fits all. If we could offer a non-destructive method on packaging of any size or shape then this could reduce the number of samples required.
Barbella: How is 3D printing/additive manufacturing impacting orthopedic device testing?
Escobedo: The ability of 3D printing of orthopedic devices is a huge breakthrough. The ability to take a CT scan of the body and create an actual replica of the body part is here. It has the promise to solve many different issues including size, inventory, patient comfort, and I would go so far to say faster time to recovery. Additionally, It could actually reduce or eliminate distribution testing. Think about the hospital or medical group having a system where the orthopedic device is produced and sterilized onsite. This could even eliminate packaging of the device. Additive manufacturing has the potential to greatly reduce the distribution channel from hundreds of miles to a few hundred feet. Why would you even need to conduct distribution testing at that point as the risk of a sterility breach would be minimized? I am not saying that 3D printing of devices would eliminate all testing. You still need to show the device being printed has the same strength and characteristics of a predicate device to last many years or even a lifetime. However, if you look at it from standpoint of eliminating packaging and distribution testing and the headache of returned devices, there is a lot of potential to reduce costs.
Barbella: In what ways has the EU’s MDR impacted orthopedic device testing?
Escobedo: We haven’t seen much of an impact from the EU’s MDR on orthopedic device testing or even medical devices in general, however, we help companies with a subset of the overall testing required for development. By the time we see the device, it has gone through rigorous design control, manufacturing, packaging, and sterilization. We then guide the clients through the distribution testing requirements and even expiration labeling. We have assisted in a few gap assessments and conducted some testing there, but there was also a significant delay from the coronavirus. We may see more activity related to the EU MDR in the future.
Barbella: How do you expect orthopedic device testing to evolve over the next 5-10 years?
Escobedo: Many other companies will be getting into the 3D orthopedic device space. Companies will have to show the devices have the characteristics of a predicate device that was manufactured in a more traditional way. Characteristics in terms of strength, either tensile or compression, or cyclic loads as examples. If the device is custom the quantity manufactured could easily be just one. Clearly, we cannot perform destructive testing on that device. To determine the device meets the required specifications, the test methods will have to be non-destructive. This will drive the need to be develop new test methods using various technologies to provide the information required for the device.
The former University of Leeds professor and decorated scientist who died last year at 90 is regarded as the father of biotribology and a pioneer in formulating elastohydrodyamic theory, a foundational concept used to describe the lubrication of gears, cams and bearings. That theory forms the basis for many of the analytical tools and methods Dowson created during his 70-year career, including a film thickness formula for hip joint prostheses that emanated from his 1960s-era research on total hip arthroplasty.
Industry pundits consider Dowson’s contributions to biotribology and elastohydrodynamic theory to be essential to the evolution of joint simulation and wear.
“Innovative numerial solutions for elastohydrodynamic lubrication problems pioneered by Dowson provided further insights into the mechanism of ankle, knee, and hip synovial joint lubrication,” a June 2020 editorial in lubricants stated. “Dowson investigated total joint replacement with an UHMWPE acetabular component, cushion bearing behaviour for knee and hip arthroplasty, and lubrication of total hip replacement joints created with materials of high elastic modulus...For more than 60 years, Duncan Dowson sustained invaluable contributions towards the advancement of total joint replacement prostheses.”
One of the most invaluable—and lasting—contributions arising from Dowson’s biotribology work was the development of knee simulators, which are used to perform wear testing of knee implants. Dowson detailed such a device for the first time in his 1977 book, “Evaluation of Artificial Joints.”
Simulators for knees, hips, and other joints reproduce both the active and natural motion of their respective parts to assess the kinematics and kinetics of total joint arthroplasty. The testing simulated by these devices allow researchers, product engineers, and manufacturers to evaluate the wear performance of their implants and bearing materials under physiological conditions. Such testing helps improve designs and leads to safer joint replacements.
ODT’s feature “Testing Complete” details the trends and market forces driving orthopedic testing and analysis. Mark Escobedo, senior sales engineer at Westpak, was among the experts interviewed for the feature; his full input is provided in the following Q&A:
Michael Barbella: Please discuss the latest trends in testing methodologies for orthopedic products.
Mark Escobedo: Like all medical devices, orthopedic devices have to maintain sterility following distribution from the point of manufacture to the point of end use. Looking at that concept from a high level, that seems fairly routine. However, orthopedic devices come in a variety of different sizes to accommodate the patient. This creates a unique situation where the device can be sent back to the manufacturer. The device may then get repackaged, need to be sterilized again, and sent back out to another hospital. How do you test for that? Are there a number of cycles that make sense? We have helped clients develop their test plan to meet this need. Each company will have specific needs depending on the product type and how the product moves through the distribution environment.
Barbella: What are the most pressing challenges facing orthopedic device testers, and what kinds of solutions are available to them?
Escobedo: Our focus is primarily on the packaging that protects the product. We need to show the packaging maintains sterility. Currently, we use two test methods that are destructive to the packaging. In addition, one test method is Qualitative in nature. This can translate into a requirement for a relatively large sample size as the qualitative data collected is considered attribute data. Once we are done testing the packaging, the device is no longer sterile. Non-destructive package testing technology does exist, but it requires custom fixturing. The challenge for us would be to offer a non-destructive test that is a “one size” fits all. If we could offer a non-destructive method on packaging of any size or shape then this could reduce the number of samples required.
Barbella: How is 3D printing/additive manufacturing impacting orthopedic device testing?
Escobedo: The ability of 3D printing of orthopedic devices is a huge breakthrough. The ability to take a CT scan of the body and create an actual replica of the body part is here. It has the promise to solve many different issues including size, inventory, patient comfort, and I would go so far to say faster time to recovery. Additionally, It could actually reduce or eliminate distribution testing. Think about the hospital or medical group having a system where the orthopedic device is produced and sterilized onsite. This could even eliminate packaging of the device. Additive manufacturing has the potential to greatly reduce the distribution channel from hundreds of miles to a few hundred feet. Why would you even need to conduct distribution testing at that point as the risk of a sterility breach would be minimized? I am not saying that 3D printing of devices would eliminate all testing. You still need to show the device being printed has the same strength and characteristics of a predicate device to last many years or even a lifetime. However, if you look at it from standpoint of eliminating packaging and distribution testing and the headache of returned devices, there is a lot of potential to reduce costs.
Barbella: In what ways has the EU’s MDR impacted orthopedic device testing?
Escobedo: We haven’t seen much of an impact from the EU’s MDR on orthopedic device testing or even medical devices in general, however, we help companies with a subset of the overall testing required for development. By the time we see the device, it has gone through rigorous design control, manufacturing, packaging, and sterilization. We then guide the clients through the distribution testing requirements and even expiration labeling. We have assisted in a few gap assessments and conducted some testing there, but there was also a significant delay from the coronavirus. We may see more activity related to the EU MDR in the future.
Barbella: How do you expect orthopedic device testing to evolve over the next 5-10 years?
Escobedo: Many other companies will be getting into the 3D orthopedic device space. Companies will have to show the devices have the characteristics of a predicate device that was manufactured in a more traditional way. Characteristics in terms of strength, either tensile or compression, or cyclic loads as examples. If the device is custom the quantity manufactured could easily be just one. Clearly, we cannot perform destructive testing on that device. To determine the device meets the required specifications, the test methods will have to be non-destructive. This will drive the need to be develop new test methods using various technologies to provide the information required for the device.