This article describes in detail the approach to be applied with respect to computational modeling and engineering analysis to be conducted in the course of non-clinical testing of the products in order to assess their materials and characteristics.
The Food and Drug Administration (FDA or the Agency),the US regulating authority in the sphere of healthcare products, has published a draft guidance document dedicated to orthopedic non-spinal bone plates, screws, and washers in the context of 510(k) premarket notification submissions.
Once finalized, the document will provide an overview of the applicable regulatory requirements, as well as additional clarifications and recommendations to be taken into consideration by medical device manufacturers and other parties involved in order to ensure compliance thereto.
At the same time, provisions of the guidance are non-binding in their legal nature, nor are they intended to introduce new rules or impose new obligations. Moreover, the authority explicitly states that an alternative approach could be applied, provided such an approach is in line with the existing legislation and has been agreed with the authority in advance.
The scope of the guidance covers, inter alia, the aspects related to non-clinical testing to be carried out in order to evaluate the material and performance characteristics of the product in question. This includes, among others, computational modeling and engineering analysis.
Computational Modeling: Overview
According to the guidance, Computational Modeling (e.g., finite element analysis) and Engineering Analysis (e.g., dimensional comparison and theoretical calculation of mechanical performance based on empirical models) can be used as an alternative to demonstrate that the mechanical behavior of the worst-case subject plates and screws are expected to be equal to or better than the predicate devices.
The authority also mentions that some of the design aspects, for example, changes in geometries over the device length or differences in material used, could impact the performance and characteristics of the device while such an impact would be difficult to assess. Thus, additional validation testing could still be required in order to confirm the results obtained via computational testing.
The document also outlines the endpoints to be met in order for the results of computational analysis to be used without additional confirmation in another (physical) way. In this respect, the authority refers to a separate guidance document dedicated to reporting of computational modeling studies in medical device submissions for additional clarifications regarding model validation and reporting.
Engineering Analysis: Key Points
As further explained by the FDA, an engineering analysis can be used in lieu of bench testing to support substantial equivalence of the yield strength and structural bending stiffness of a plate if the predicate plate dimensions and material properties (modulus and yield strength) are known, and if the predicate plate is manufactured utilizing the same device material and manufacturing materials and processes as the subject device.
A similar approach could be applied with respect to screws, allowing to assess their torsional performance based on the dimensions of the predicate and the device in question, provided the materials used and manufacturing processes employed are the same.
Thus, the approach to be applied in the case of engineering analysis would also require establishing a substantial equivalence demonstrating that both the existing medical device already placed on the market (predicate) and the new medical device subject to review are similar in terms of materials used, design, and characteristics.
In order to ensure the accuracy and reliability of the results of engineering analysis, the manufacturers should follow the approach described in the present guidance. In particular, the document outlines the scope of dimensions to be used when comparing the product in question to the predicate. According to the guidance, these dimensions should include:
- Thread ShearAarea
- Axial thread length including only threads that have the nominal major diameter where complete purchase is expected of thread engagement in material
- Major diameter
- Thread depth
- Minor (root diameter)
- Thread pitch
The authority additionally emphasizes that all such dimensions should be reflected in supporting documentation. Moreover, the values used for the above calculations should meet the ones indicated in the engineering drawings for the product.
Furthermore, the authority expects medical device manufacturers to provide the appropriate justification of why the products used could be considered worst-case, as in accordance with the guidance.
The above assessment should be conducted using the worst-case products in order to ensure the accuracy and reliability of its results.
In order to assist medical device manufacturers and other parties involved, the authority highlights certain specific aspects related to computational modeling and engineering analysis to be taken into consideration when performing such assessment.
For instance, with respect to engineering analysis, the authority mentions that: axial pullout performance is heavily influenced by the amount of interface and the failure mechanism at the interface with bone foam; factors such as decreasing outer diameter and decreasing axial thread length may help identify the worst case.
In summary, the present FDA draft guidance provides an overview of the approach to be applied with respect to computational modeling as a method used to assess the characteristics and performance of a medical device in question without conducting physical testing. The document also highlights the key points related to the engineering analysis and describes in detail the way it should be conducted, and also the main considerations associated thereto.
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