Patient-Specific Implants and Proper Testing of Them—An Orthopedic Innovators Q&A

By Sean Fenske, Editor-in-Chief
 
With the advent of sophisticated software solutions and new manufacturing methods, the opportunity to fabricate patient-specific implants has become a reality. Developed from each patient’s medical scans, these implants can offer an improved fit for patients and may also lead to additional benefits such as faster recovery time.
 
On the other hand, patient-specific implants bring new challenges with regard to testing. How can a manufacturer test a device with a quantity of one? When each implant is custom fabricated to each patient, how does testing ensure the final product is safe? There are a number of questions that need to be addressed before a company can begin on the patient-specific implant pathway.
 
Fortunately, Stacey Barber, technical manager at Empirical Technologies, has taken time to address a number of questions around patient-specific implants and the testing involved with them. In the following Q&A, she responds to inquiries on several factors, including the technology making these implants possible, proper testing protocols, and often overlooked considerations.
 
Sean Fenske: What’s the trend with patient-specific implants? Is this still just emerging, rapidly growing, or already fairly established?
 
Stacey Barber: I would say patient-specific devices are becoming increasingly common in recent years and are still rapidly growing.
 
Fenske: Where are patient-specific implants being used most often? Are they all orthopedic implants or more common for certain areas?
 
Barber: Patient-specific implants are being used from head to toe for uses including cranial plates or temporomandibular joint (TMJ) implants to foot plates and ankle replacement devices. Patient-specific devices are even used in prosthetic limbs. We tend to see patient-specific devices being used for bone fractures, for situations where several defects exist like oncological or congenital malformation, or in areas where restoring complex three-dimensional (3D) geometries is challenging.
 
Fenske: What manufacturing processes are making patient-specific implants a reality? Is it additive manufacturing or are other technologies being used?
 
Barber: Rapid prototyping and additive manufacturing are the driving force behind making patient-specific devices a reality, but this also goes hand in hand with computer-aided design software, simulation software, and various imaging techniques that allow for reverse engineering the areas of interest.
 
Fenske: When developing truly patient-specific implants such that each implant is unique, how do you properly test that? You can’t select a single sample from a batch, can you?
 
Barber: Patient-specific devices still come with some level of design constraints. We at Empirical Technologies approach patient-specific devices by identifying the extreme differences the design can have (e.g., material thickness, extreme offsets, extreme implanting conditions, least material conditions, to name a few). Once we have identified the extreme ends of the spectrum in which the device can change, we then create a rationale for a worst-case patient-specific device within those design controls and we can test several samples made to those worst-case conditions. In addition, finite element analysis (FEA) of different designs is also growing increasingly common, however, you have to have validated models, which often requires testing actual devices and verifying that the outputs from the FEA are matching the outputs of the actual testing.
 
Fenske: Does testing show significant improvements in performance with patient-specific implants? Or do they simply offer a better fit for patients?
 
Barber: Typically, the goal is to offer a better fit to the patient. The idea here would be to increase the precision of the design against the patient geometry, which could, in turn, decrease or eliminate modifications to the surgical site or implants themselves. This can result in shortened operation times, more comfort to the patient, and possibly even a faster healing process.
 
Fenske: What testing considerations are important with patient-specific implants that manufacturers may overlook? Are there testing processes that are different from standard implants?
 
Barber: Testing consideration for patient-specific devices usually follow the same process and testing methods as standard implants. Since most patient-specific devices tend to be additively manufactured, there could be extra requirements based on the currently evolving requirements for additively manufactured devices but not specifically just because the devices are patient specific.
 
Fenske: Do you have any additional comments you’d like to share based on any of the topics we discussed or something you’d like to tell orthopedic device manufacturers?
 
Barber: Take the time to thoroughly explore the design constraints of your patient-specific device and ensure you are identifying the worst case design. This can be a challenging process, so it is very important to work through all foreseen scenarios. FEA can be a useful tool but should not be solely relied upon.
 
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