The new article highlights the aspects related to the testing to be conducted in order to assess the relevant mechanical performance of bone plates and screws.
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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Administration (FDA or the Agency), the US regulating authority in the sphere of healthcare products, has published a draft guidance document dedicated to orthopedic non-spinal bone plates, screws, and washers in the context of submissions under the 510(k) premarket notification framework. Once finalized, the guidance 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 therewith.
At the same time, provisions of the guidance are non-binding in their legal nature, nor are 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 underlying legislation and has been agreed with the authority in advance.
In particular, the scope of the guidance covers, inter alia, the aspects related to non-clinical testing the products should be subject to in order to collect data and generate evidence supporting claims made by the manufacturer in the context of the marketing submission. The document outlines the scope of testing to be conducted and highlights the key points to be taken into consideration by the parties responsible for medical devices in this respect.
Plate Mechanical Performance
First of all, the authority mentions that loss of fracture reduction or construction stiffness can cause incomplete or absent osteosynthesis leading to device failure and revision surgery; thus, mechanical performance testing will be required to ensure the product is able to perform as expected. For this purpose, the authority recommends to perform a single-cycle bend testing where the worst-case subject plate is used (also considering the worst-case load-bearing region). With respect to the test itself and the way it should be carried out, the authority refers to the applicable standard which is ASTM F382 Standard Specification and Test Method for Metallic Bone Plates.
Additional aspects to be taken into consideration when planning and conducting such testing should include the plate thickness, length, and shape of the product in general. However, the authority also mentions that certain modifications to the test setup described in the abovementioned standard could be accepted, provided they are reasonably necessary to accommodate specifics of the device and are duly justified. As a result of the said testing, the details on bending structural stiffness and bending strength should be obtained.
In order to ensure the proper evaluation of test results, the authority recommends the responsible parties to provide additional information about subjects and tests in accordance with the aforementioned standard and recommendations provided therein. The said information is expected to be structured as a table, highlighting the differences in test methods applied, together with the proper explanation of why these differences are not supposed to affect the accuracy and reliability of test results.
Furthermore, the authority also mentions that in the case of similar medical devices having the same design and composition in terms of materials used, fatigue bend testing would not be required. At the same time, such testing would be required in case there are differences in technologies (for instance, related to the materials used, device design, or modularity). The authority mentions that plates with their worst-case structurally critical region present in the uniform portion of the plate shaft are expected to show similar trends when comparing static performance and fatigue performance (if applicable).
According to the guidance, a party responsible for a medical device in question is also allowed to choose a method, alternative to what is described in the aforementioned standard. Should it be the case, the aspects to be considered with respect to the design of the test setup should include the worst-case clinically relevant loading, clinically relevant loading modes (e.g., axial compression, bending, torsion), differences in material properties, and differences in dimensions and geometry of the subject and predicate devices.
According to the guidance, in the case of plates utilizing anisotropic materials, and if bending contouring is not explicitly discouraged in the labeling for the product, the authority would also expect the details on additional testing or sufficient scientific justification confirming the product maintains mechanical performance during the normal use for its intended purpose.
Screw Mechanical Performance
The scope of the guidance also covers the aspects related to the screw’s mechanical performance. As explained by the authority, their inappropriate performance could result in a fraction in the course of use. Thus, torsional strength analysis will be required to provide the necessary assurance of the product and material strength. Furthermore, improper performance could result in loss of fixation, so the pullout strength analysis will be required to address the aspects related to the fixation strength.
With respect to the above, when assessing the mechanical performance of screws, the authority recommends to conduct the following types of testing:
– Insertion/removal torque testing,
– Torsional strength testing, and
– Pullout strength testing per ASTM F543 Standard Specification and Test Methods for Metallic Medical Bone Screws.
Apart from that, the engineering analysis could be applied in order to assess compliance of the product in question with the requirements and specifications set forth by the relevant FDA-recognised standards.
All the testing should be performed on the worst-case screws, taking into consideration the most critical parameters. The document further describes specific aspects to be considered and also outlines the scope of testing results to be included in the submission.
In summary, the present FDA draft guidance provides additional clarifications regarding the testing plates and screws should be subject to in order to assess their mechanical characteristics which are vitally important in the context of the intended use of such products. The document highlights the key points to be taken into consideration when planning the design and conducting the said testing in order to ensure the accuracy and reliability of the results.
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