Comparison of the Pullout Strength of Pedicle Screws According to the Thread Design for Various Degrees of Bone Quality
Round 1
Reviewer 1 Report
Congratulations on the well-organized manuscript that you have prepared. However, there are some comments that can help you increase the quality of the article prior to publishing:
in the introduction part, you can mention the materials that are used for pedicle screws. as an example, NiTi screws are widely used in recent researches for biomedical applications. on the other hand, introducing some external materials to the human body may cause these materials to corrode and release some metallic ions. So, it might be useful if you mention some of the coating techniques used for biomedical applications. it is better to add a short paragraph and add some discussion about this stuff. the following are some new references that can compensate for the very old references you have right now:
https://link.springer.com/article/10.1007/s10853-019-03375-1
https://www.mdpi.com/2076-3417/9/3/586
https://www.sciencedirect.com/science/article/pii/S0268003318308350
https://thejns.org/spine/view/journals/j-neurosurg-spine/28/6/article-p679.xml
https://nrs.org/journal/pnrs/browse-the-journal/volume-2/sol-gel-process-applications-a-mini-review
https://journals.sagepub.com/doi/abs/10.1177/2192568218824080
there are some minor English typos in the manuscript that should be removed by a second time reading of the text. as an example, in line 75, it should be "...compared to human vertebra..."
are the foam densities standard by the manufacturer or you selected them yourself? the difference between low and medium density is 160 but between medium and high is 480 which is 3 times more than the previous one.
table 2 mentions that the density of the pedicle screws is 4430000 kg/m3. is that correct? it is around 200 times more than the density of osmium (densest metal)!!!!!!
in table 3, please fix the divider line between screw types and foam/bone types.
please add a conclusion section after the discussion section and mention the findings of this study in bullet points. a paper must have a separate conclusion part not mixed in the discussion of the paper.
Good luck!
Author Response
Responses to Reviewer 1 comments
Thank you for excellent and helpful comments on the manuscript. With delight, we tried to follow a reviewer’s comment, which markedly improved the quality of this manuscript. We appreciate for giving one more opportunity to resubmit the revised manuscript.
Point 1: In the introduction part, you can mention the materials that are used for pedicle screws. As an example, NiTi screws are widely used in recent researches for biomedical applications. On the other hand, introducing some external materials to the human body may cause these materials to corrode and release some metallic ions. So, it might be useful if you mention some of the coating techniques used for biomedical applications. It is better to add a short paragraph and add some discussion about this stuff.
Response 1: We appreciate for this comment. We think a reviewer pointed out an important issue. We stated the materials used for pedicle screws and mentioned material related corrosion and coating techniques in the “Introduction” section. Furthermore, we added a paragraph discussing coating techniques used for biomedical applications in the “Discussion” section.
Point 2: There are some minor English typos in the manuscript that should be removed by a second time reading of the text. As an example, in line 75, it should be "...compared to human vertebra..."
Response 2: Authors are sincerely grateful for the excellent comments. As a reviewer’s comment, we have refined the manuscript and changed the words with English typos.
Point 3: Are the foam densities standard by the manufacturer or you selected them yourself? The difference between low and medium density is 160 but between medium and high is 480 which is 3 times more than the previous one.
Response 3: Thank you for excellent comments. We selected the foams with low (160 kg/m3), medium (320 kg/m3), and high (800 kg/m3) densities to simulate human osteoporotic cancellous bone, normal cancellous bone, and cortical bone, respectively, according to American Society for Testing and Materials (ASTM F1839-01) protocol [1], and the selection strategy of which was concordance with previous published study [2]. Therefore, the density difference between medium and high is not identical to that between low and medium.
1. ASTM F1839-01. Standard specification for rigid polyurethane foam for use as a standard material for testing orthopedic devices and instrument; ASTM international: West Conshohocken, PA, USA, 2001.
2. Brasiliense LB, Lazaro BC, Reyes PM, Newcomb AG, Turner JL, Crandall DG, et al. Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines. Spine J. 2013, 13, 947–956.
Point 4: Table 2 mentions that the density of the pedicle screws is 4430000 kg/m3. Is that correct? It is around 200 times more than the density of osmium (densest metal)!!!!!!
Response 4: We appreciate for an excellent comment. We have to apologize that we made a mistake during unit conversion. The value for density of pedicle screws should be 4430 kg/m3. However, as the reviewer 2 pointed out, we modified the manuscript focusing on the mechanical testing protocol and deleted the results of FE model analysis. Therefore, the contents of Table 2 related to FE model study were deleted either.
Point 5: In table 3, please fix the divider line between screw types and foam/bone types.
Response 5: Authors appreciate for a reviewer’s comment. As the referee pointed out, we fixed the divider line between screw types and foam/bone types in table 3.
Point 6: Please add a conclusion section after the discussion section and mention the findings of this study in bullet points. A paper must have a separate conclusion part not mixed in the discussion of the paper.
Response 6: Thank you for comments. Authors agree with a reviewer’s opinion. Therefore, we added a separate conclusion section after the discussion section mentioning the findings of this study, which would make the paper more formal.
Reviewer 2 Report
Dear Author
In the definition of the study aim I suggest to consider the findings of Brasiliense et al. "Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines Author links open overlay pane" that has already characterized the mechanical performances of single and double-threaded screws using a cadaveric model.
line 69-71: include this information as list.
line 99: include the dimensions of the "rigid frame" and how they relate to the ASTM standard.
line 134: include details on the simulation of the screw insertion, How the pilot hole of 2.7mm was modeled?
line 147: indicate the failure criteria adopted for the bone surrogate material.
line 164: disclose screw supplier.
line 195: describe the validation in terms of quantitative, numerical results.
Figure 7: the contact formulation described in the method section is not compatible with stresses at the tip for a pullout loading condition.
line 272: FE analysis is a reliable tool but the manuscript leak of an actual validation of the model.
line 290: this is not an in vitro study but a mechanical testing performed on bone surrogates.
everywhere in the manuscript: indicate kilo Newtons with [kN].
While the aim of comparing the two different designs is justified by the mechanical testing proposed, the rationale for the FE modeling it is not clear since the results of the FE modeling are not clearly are not validated, exposed, and actually used to answer the main research question.
I invite you to focus on the mechanical testing and reformulate your aim considering the already disclosed results of existing studies.
Author Response
Responses to Reviewer 2 comments
Thank you for excellent and helpful comments on the manuscript. With delight, we tried to follow a reviewer’s comment, which markedly improved the quality of this manuscript. We appreciate for giving one more opportunity to resubmit the revised manuscript.
Point 1: In the definition of the study aim I suggest to consider the findings of Brasiliense et al. "Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines Author links open overlay pane" that has already characterized the mechanical performances of single and double-threaded screws using a cadaveric model.
Response 1: Authors appreciate for the excellent comments. Authors agree with a reviewer’s opinion. Therefore, we added the results of biomechanical testing on our newly designed double dual-threaded pedicle screw in the manuscript. We found that the double dual-threaded screw exhibited better mechanical performance compared to single-treaded screw in osteoporotic bone with bicortical bone margin, which revealed different characteristic of screw with dual-threaded design compared to previous study conducted by Brasiliense et al.
Point 2: While the aim of comparing the two different designs is justified by the mechanical testing proposed, the rationale for the FE modeling it is not clear since the results of the FE modeling are not clearly are not validated, exposed, and actually used to answer the main research question.
I invite you to focus on the mechanical testing and reformulate your aim considering the already disclosed results of existing studies
Response 2: we are sincerely grateful for the excellent comments. We think a reviewer pointed out an important issue. Therefore, following a reviewer’s comments, we modified the manuscript focusing on the mechanical testing protocol and deleted the results of FE model analysis. Furthermore, considering the already disclosed results of existing studies, we added biomechanical testing results of our newly designed double dual-threaded screw in the manuscript, and reformulated our aim in the “Introduction” section.
Point 3: line 69-71: include this information as list.
Response 3: Authors appreciate for the comment. As a reviewer pointed out, we deleted the statements describing the structure of the pedicle screws, and included the information under table 1.
Point 4: line 99: include the dimensions of the "rigid frame" and how they relate to the ASTM standard.
Response 4: Thank you for the comment. As the referee pointed out, we included the dimensions of the “rigid frame”, and stated how the testing machine related to the ASTM standard in the “Material and Method” section.
Point 5: line 134: include details on the simulation of the screw insertion, How the pilot hole of 2.7mm was modeled?
Response 5: We appreciate for the comment. Following a reviewer’s comments, we modified the manuscript focusing on the mechanical testing protocol and deleted the results of FE model analysis. Therefore, there is no response for this comment.
Point 6: 147: indicate the failure criteria adopted for the bone surrogate material.
Response 6: Thank you for the comment. Because we modified the manuscript focusing on the mechanical testing protocol and deleted the results of FE model analysis following a reviewer’s comments, there is no response to this comment.
Point 7: line 164: disclose screw supplier.
Response 7: Authors appreciate for an excellent comment. The screw supplier was TJC life biotechnology company, and we added the disclosure under table 2.
Point 8: line 195: describe the validation in terms of quantitative, numerical results.
Response 8: We are grateful for the excellent comment. As we modified the manuscript focusing on the mechanical testing protocol and deleted the results of FE model analysis, there is no response to this comment.
Point 9: Figure 7: the contact formulation described in the method section is not compatible with stresses at the tip for a pullout loading condition.
Response 9: Authors appreciate for a reviewer’s comment. Following a reviewer’s comments, we modified the manuscript focusing on the mechanical testing protocol and deleted the results of FE model analysis. Therefore, Figure 7 was deleted either, and there is no response for this comment.
Point 10: line 272: FE analysis is a reliable tool but the manuscript leak of an actual validation of the model.
Response 10: We appreciate for this comment. As we modified the manuscript focusing on the mechanical testing protocol and deleted the results of FE model analysis, there is no response for this comment.
Point 11: line 290: this is not an in vitro study but a mechanical testing performed on bone surrogates.
Response 11: Thank you for the excellent comments. Authors agree with a reviewer’s opinion. Therefore, we changed the words “an in vitro study” to “a biomechanical testing study” in the last paragraph of the “Discussion” section.
Point 12: everywhere in the manuscript: indicate kilo Newtons with [kN].
Response 12: Authors appreciate for a reviewer’s comment. As the referee pointed out, we indicated kilo Newtons with [kN] everywhere in the manuscript.
Round 2
Reviewer 2 Report
Thanks for addressing my comments. I belive that this new version reflects all the changes requested.
