Analysis of alternate material Onyx™ for total knee arthroplasty instrumentation sets
-
Nathan Gregg
,
Alyssa M. Kendrick
,
Jill M. Carter
,
Mark E. Gittins
Abstract
Context
A 25-pound weight limit is currently set on containerized instrumentation sets by the Association of periOperative Registered Nurses (AORN) and the Association for the Advancement of Medical Instrumentation (AAMI), in order to reduce strain on the staff and ensure that the sets are not too crowded in order to preserve sterilization and drying of the instruments. This is pushing companies to reduce the weight and number of instrumentation sets for the operating room. One solution has been to explore the viability of new, lighter materials such as Onyx.
Objectives
The goal of this study is to evaluate the novel material Onyx as a viable material utilized in reusable total knee arthroplasty (TKA) instrumentation sets utilizing traditional steam sterilization as the sterilization method.
Methods
Mechanical and biocompatibility tests according to the American Society for Testing Materials (ASTM) and International Organization for Standardization (ISO) 10,993 were run to evaluate the Onyx Material to see if it would be a viable alternative to the stainless and martensitic steel that is currently being utilized.
Results
Gross warping and cracking after 10 rounds of sterilization was observed. This was qualitatively worse in the Onyx without a carbon fiber component. The Onyx material did not meet biocompatibility standards for its application.
Conclusions
Onyx was determined to not be a viable material for TKA instruments regarding multiple high-pressure and -temperature sterilizations and cytotoxic cell testing.
The Association of periOperative Registered Nurses (AORN) and the Advancement of Medical Instrumentation (AAMI) currently limit the weight of containerized instrumentation sets to 25 pounds [1]. As a result, companies producing total knee arthroplasty (TKA) instrumentation sets as well as hospitals have come up with various methods for reducing the number of trays utilized. One method is to utilize patient-specific instrumentation that utilizes disposable single-use instrumentation in order to reduce the surgical tray weight. This method was found, in a meta-analysis of 48 articles, to reduce the surgical trays utilized by two-thirds (66.67 %). Template-directed instrumentation is another method that is utilized to reduce the number of instruments utilized but instead utilizes reusable instrumentation. This method was found to have up to 57 % reduction in tray weight [2]. A retrospective cohort study consisting of 449 patients found that utilizing the Precision single-use TKA instrumentation tray reduced the number of trays utilized and the cost by $375 to $500. They also found a statistically significant decrease in the postoperative infection rate [3]. Along with the weight requirement, the materials utilized in these instrumentation sets must endure temperatures of at least 270 °F [4] and various forces during surgery, and they must meet biocompatibility standards for its given application. Currently, most companies utilize steel and certain polymers for reusable trays. Although steel is a sturdy and more affordable material, it is also heavy, making it challenging to meet the weight requirement while limiting the number of trays. Currently, NextStep Arthropedix in Akron, Ohio is evaluating alternate lighter materials such as Onyx, which is a micro carbon fiber-filled nylon [5]
Thirty-one total components were evaluated in this study. Given the affordance of 3D printed materials, such as Onyx, to weave in other materials like carbon fiber, different weaving patterns were utilized to create these components. The purpose of this study was to evaluate if the novel material Onyx was a viable material to be used in TKA instrumentation sets based on its ability to withstand traditional steam sterilization, to meet biocompatibility standards according to its use set forth by the International Organization for Standardization (ISO), and to understand the influence of various weaving patterns on its resistance to impact forces.
Methods
Ethical approval
Institutional Review Board approval was not necessary because this activity is not research involving human studies subjects and because 45 CFR 46 does not apply.
Data collection
This study was conducted at three facilities from June 1 to August 13, 2021. The sterilization testing was conducted at OrthoNeuro in New Albany, Ohio. Biocompatibility testing was completed at Nelson Labs in Chicago, Illinois. The Izod impact testing was completed through NextStep Arthropedix.
Sterilization testing
The components were run through 10 cycles in the autoclave to evaluate their response to a minimum temperature of 270 °F, the pressure change of three atmospheres, and steam. Sterilization temperature testing was conducted with a total of 31 components. A total of 21 threaded tensile bars were broken up into three groups based on their material properties: 7 bars of Onyx without a carbon fiber component, 7 bars of Onyx with a longitudinal carbon fiber component, and 7 bars of Onyx with a woven carbon fiber component, in addition to 10 trial components that were 3D-printed Onyx without a carbon fiber component. Each group of items were run through 10 cycles of sterilization. After each round of sterilization, the components were photographed to assess qualitative deformation and measured utilizing a digital caliper in marked planes along the x, y, and z axes to assess for quantitative deformation.
Cytotoxicity testing
Biocompatibility testing for cytotoxicity was conducted at Nelson Labs according to the specific application of the material under ISO 10993 Table A.1 [6]. The application according to this table was defined as an externally communicating device that was in contact with tissue/bone/dentin for less than 24 h. In order to test for biocompatibility, the material was extracted in serum-supplemented mammalian cell culture media (minimum essential media [MEM]). After extraction, the extracts were placed in contact with a monolayer of L-929 cells (mouse fibroblasts). The cells were then allowed to grow in the extraction fluid for 24 h before being evaluated. This evaluation was qualitatively performed by observing the cells under the microscope and assigning a cytotoxic grade (0–4) based on an estimated percent lysis and the morphology of the cells. In this scale, 0 represented nonreactive and 4 would be severely reactive. An acceptable score would be 2 (mildly reactive) or less.
Izod impact testing
The material’s resistance to impact was evaluated based on an Izod impact test according to the American Society for Testing Materials (ASTM) standard D638. This test is performed by striking a sample of the material with a pendulum at increasing impact energies until it fractures and breaks as shown in Figures 1 and 2. This force required to fracture the material is measured by the distance traveled by the hammer after a fracture.
An example of the impact testing apparatus and process.
Results
Sterilization testing
The first signs of deformation were observed after the second round of sterilization. The deformation became more prominent as the trial components continued through all 10 cycles. As shown in Figure 3, the deformations observed were cracks, warping of the femoral surface, and minor erosion of the material. The most notable qualitative deformations observed were in the components without carbon fiber. The bearing trials made of only the Onyx material had noticeable gross deformations with bowing and erosion. The bearing trials with woven carbon fiber and the longitudinal carbon fiber displayed less bowing but did show erosion of the Onyx. The measurements utilizing the calipers did not show any significant changes in the dimensions of length, width, and height for these components.
The apparatus utilized to conduct the Izod impact testing.
Cytotoxicity testing
There were two rounds of cytotoxicity testing to evaluate if there was an effect of the cleaning method of the test components. As mentioned previously, the acceptable scoring range for this test was <2. The components utilized for the first cytotoxicity test were cleaned utilizing an alcohol cleaning method similar to cleaning ultra-high-molecular-weight polyethylene. The first round of cytotoxicity testing resulted in a score of 3, which is not considered passing. The components utilized for the second cytotoxicity test were cleaned utilizing an aqueous cleaning system. This round of testing resulted in an average score of 4, which is still not passing.
An image of the trial components built with no carbon fiber after 10 rounds of traditional steam sterilization demonstrating wear from sterilization.
Izod impact testing
The Izod impact testing conducted resulted in an impact energy of 2.42 J for Onyx without a carbon fiber component, 13.13 J for Onyx with a woven carbon fiber component, and 21.19 J for Onyx with a longitudinal carbon fiber component. These values are an average of three Izod impact tests that were performed for each material to provide a more accurate representation of the energy required to fracture the material. These values are listed in Table 1.
Izod impact energies for Onyx with and without carbon fiber.
| Material tested | Izod impact energies (Joules) |
|---|---|
| Onyx without a carbon fiber component | 2.42 |
| Onyx with a woven carbon fiber component | 13.13 |
| Onyx with a longitudinal carbon fiber component | 21.19 |
Discussion
The observed deformations and the lack of change in dimensions for the components during the sterilization cycles were conflicting. However, because these components were 3D-printed, they were built in layers. This likely led to visible deformation in the surface layers of these components that was not measured in the designated planes represented in the quantitative data. The resulting deformations would still preclude the material from being sterilized utilizing traditional steam sterilization. The integration of woven and longitudinal carbon fiber likely added structural integrity and likely explains why these components demonstrated less deformation and bowing.
When researching the material, the heat of deflection was found to be 293 °F according to Markforged’s website. Originally, it was thought this would be high enough above the 270 °F sterilization temperature that deformation would not be seen. However, this heat of deflection is based on the material’s properties at one atmosphere of pressure. Due to the relationship between temperature and pressure on the physical state of materials, the positive and negative pressure changes of a sterilization cycle also altered the heat of deflection. During these pressure drops, the heat of deflection likely decreased below the 270 °F mark, leading to the deformations seen.
The Izod impact energies were significantly lower than that of stainless steel, which is the primary material utilized for surgical instrumentation [7]. This difference was expected and acceptable. Steel has an impact energy of 150J [8], which is much higher than needed for surgical applications. If the cytotoxicity and sterilization testing had not failed, then a formative simulated-use test would have been conducted for the high-impact components to further assess their response to the impact forces during surgery.
While there are multiple characteristics that would make Onyx a viable material, this study only focused on three key qualifying characteristics. In future studies, other tests would need to be run, such as actual-use validation, in which the instrumentation would be built from the material being tested and utilized the same as in surgery [9].
Furthermore, the digital calipers utilized to measure deformities were insufficient for identifying small changes in the material after sterilization. This system of measurement gives too much room for human error despite measuring the same marked plane along the x, y, and z axes with each cycle. A better measurement system for future studies would be an optical measurement system such as a Field of View Image-Based measurement system [10].
Conclusions
Traditional high-temperature and -pressure sterilization techniques would not be a viable sterilization method for Onyx due to the distortion of the material. This material is also limited by its lack of biocompatibility for the use of an externally communicating device that was in contact with tissue/bone/dentin for less than 24 h. It could be considered for single-use instrumentation in components that are noncommunicating with the patient. These findings also indicate the need for further research on similar materials for single-use or multi-use instrumentation. Despite having negative findings for the Onyx material, this study demonstrates the robust demands of instrumentation and provides data and understanding for future studies of lighter materials to be tested in the future.
-
Research funding: None reported.
-
Author contributions: All authors provided substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; N.G., A.M.K., and J.M.B. drafted the article or revised it critically for important intellectual content; M.E.G. gave final approval of the version of the article to be published; and all authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
-
Competing interests: Sarah C. MacNeill, MS, PAC has relationships with Ethicon (paid consultant for company or supplier) and Smith & Nephew (paid consultant for company or supplier). Mark E. Gittins, DO, FAOAO has relationships with NextStep Arthropedix (royalties from company or supplier), DePuy Synthes (research support from a company or supplier as principal investigator), Medacta (paid consultant for company or supplier), and Smith & Nephew (paid consultant for company or supplier).
References
1. Containment devices for reusable medical device sterilization. ANSI/AAMI ST77:2013/(R)2018; Containment devices for reusable medical device sterilization [Published online February 1, 2013].Search in Google Scholar
2. dos Santos, BM, Fogliatto, FS, Zani, CM, Peres, FA. Approaches to the rationalization of surgical instrument trays: scoping review and research agenda. BMC Health Serv Res 2021;21:163. https://doi.org/10.1186/s12913-021-06142-8.Search in Google Scholar PubMed PubMed Central
3. Siegel, GW, Patel, NN, Milshteyn, MA, Buzas, D, Lombardo, DJ, Morawa, LG. Cost analysis and surgical site infection rates in total knee arthroplasty comparing traditional vs. single-use instrumentation. J Arthroplasty 2015;30:2271–4. https://doi.org/10.1016/j.arth.2015.05.037.Search in Google Scholar PubMed
4. Steam sterilization. Centers for Disease Control and Prevention. September 18, 2016. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/sterilization/steam.html#:∼:text=The%20two%20common%20steam%2Dsterilizing,minimal%20time%20to%20kill%20microorganisms [Accessed 9 June 2023].Search in Google Scholar
5. Onyx – composite 3D printing material. Markforged. 2023. https://markforged.com/materials/plastics/onyx?utm_source=google&utm_medium=paid-search&utm_campaign=11874126436&utm_content=147173319775&utm_term=&gclid=CjwKCAjwm4ukBhAuEiwA0zQxk9xPlqWultKDU2bxgTzSKL0O5sSFt4m89C87dOKsomv-hbFpKC1w4RoCIZQQAvD_BwE [Accessed 9 June 2023].Search in Google Scholar
6. Center for Devices and Radiological Health. U.S. Food and drug administration; 2020. https://www.fda.gov/media/85865/download [Accessed 9 June 2023].Search in Google Scholar
7. Saint, L. The best metals and materials for surgical instruments. Sheffield, UK: Cairn Technology LTD. November 29, 2022. https://cairntechnology.com/the-best-metals-and-materials-for-surgical-instruments/#:∼:text=Stainless%20steel%20has%20been%20the,where%20hygiene%20is%20a%20priority [Accessed 18 June 2023].Search in Google Scholar
8. Peckner, D. Handbook of stainless steels. Blacklick, OH: McGraw-Hill; 1977.Search in Google Scholar
9. Human factors studies and related clinical study considerations in combination product design and development. Food and Drug Administration. February 2016. https://www.fda.gov/files/about%20fda/published/Human-Factors-Studies-and-Related-Clinical-Study-Considerations-in-Combination-Product-Design-and-Development.pdf [Accessed 18 June 2023].Search in Google Scholar
10. W P. Field of View image-based measurement systems. Sipcon. October 11, 2021. https://sipconinstrument.com/blog/field-of-view-image-based-measurement-systems/ [Accessed 18 June 2023].Search in Google Scholar
© 2023 the author(s), published by De Gruyter, Berlin/Boston
This work is licensed under the Creative Commons Attribution 4.0 International License.
Articles in the same Issue
- Frontmatter
- Innovations
- Original Article
- Analysis of alternate material Onyx™ for total knee arthroplasty instrumentation sets
- Medical Education
- Original Article
- Impact of the USMLE Step 1 and COMLEX Level 1 transition to Pass/Fail on osteopathic medical student stress levels and board preparation
- Musculoskeletal Medicine and Pain
- Original Article
- Ultrasound-guided injection through the rotator cuff interval: a clinical perspective of one institution’s results and description of technique
- Neuromusculoskeletal Medicine (OMT)
- Clinical Practice
- Integrating osteopathic manipulative treatment into prenatal care visits in a family medicine resident clinic
- Public Health and Primary Care
- Original Article
- The effectiveness of disinfection protocols in osteopathic family medicine offices
- Clinical Image
- Lichen planus pigmentosus inversus: a rare clinical variant
- Abstracts
- 2023 AOA Research Abstracts and Student Poster Competition
Articles in the same Issue
- Frontmatter
- Innovations
- Original Article
- Analysis of alternate material Onyx™ for total knee arthroplasty instrumentation sets
- Medical Education
- Original Article
- Impact of the USMLE Step 1 and COMLEX Level 1 transition to Pass/Fail on osteopathic medical student stress levels and board preparation
- Musculoskeletal Medicine and Pain
- Original Article
- Ultrasound-guided injection through the rotator cuff interval: a clinical perspective of one institution’s results and description of technique
- Neuromusculoskeletal Medicine (OMT)
- Clinical Practice
- Integrating osteopathic manipulative treatment into prenatal care visits in a family medicine resident clinic
- Public Health and Primary Care
- Original Article
- The effectiveness of disinfection protocols in osteopathic family medicine offices
- Clinical Image
- Lichen planus pigmentosus inversus: a rare clinical variant
- Abstracts
- 2023 AOA Research Abstracts and Student Poster Competition
