Biomechanical Comparison of Different Volar Screw Placements for Horizontal Oblique Scaphoid Fractures

Round 1

Reviewer 1 Report

The manuscript is devoted to biomechanically compare the fixation strength of central and eccentric screw placement for the volar fixation of horizontal oblique scaphoid fractures. Evaluation of the screw-bone stiffness, as well as of their ultimate load, were performed, confirming the Authors hypothesis that the central placements provide better strength compared to the eccentric one.

The biomechanical testing was performed in the worst screw-bone fixture condition: with a gap of 2 mm between the proximal and distal fragments. The quality of the paper is good, as well as the English language.

According to the reviewer the following main points have to be considered:

1. Table 1: To have a clearer table to read, collapse the “Age” and “Gender” fields in only one cell for each cadaver.
2. Line 73, add the deg symbol to 60.
3. Lines 93-94. It is not very clear why the Authors, as well as in Ref 10, pass the Kirschner wire through the proximal end of the scaphoid. Does it provide a better fixation in the PMMA holder? Can the Authors explain this choice?
4. Line 102. Insert the maximum load capacity of the testing machine.
5. Lines 106-107. For a better understanding of the stiffness calculation it would be better to insert two figures, one for a central screw position case and the other for an eccentric screw position case, where the load (in Newton) vs. displacement (in mm) curve is reported and where the region of stiffness calculation are highlighted.
6. Lines 130-131. It would be better to report two figures with the failed screw-bone system, one for the central and the other for the eccentric screw configuration.

For all the previous reasons, the reviewer recommends minor amendments of paper for publication in Applied Sciences.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The authors present an interesting article where they biomechanically compared the fixation strength between central and eccentric screw placements for volar fixation of horizontal oblique scaphoid fractures. Overall, the article is very well written with the objectives, methodology and results presented in a clear and concise manner. Likewise the discussion, which thoroughly highlighted the reasons behind some of their study choices (as opposed to the literature) – horizontal oblique fractures, volar fixation, central/eccentric placement, and the limitations – cadaver samples, sample age, screw placement, clinical outcomes etc  

I only have one minor issue – subheading 2.3 should be changed to “statistical analysis” or similar as it is already used in section 2.2 and does not adequately describe what is written.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors

I am very pleased to have a chance to review your paper and I enjoyed reading it. I think it is very well written paper, very interesting and that it should be published. 

I have couple of remarks and questions.

First I would like you to describe more precisely how you created 2 mm gap. Did you perform distraction, or you made additional cut of the scaphoid? If you made distraction, than your calculation of screw lenght is not appropriate.

And how did you mantain correct position of the guidewire? 

Also it would be interesting to know where did the bone-screw construct fail, on proximal or distal part? And if there were the difference between central or eccentric screw placement?

Thank you

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

This study shows an experimental study to reveal insights on the waist fracture induced by the presence of screws. Although there are several aspect of the methodological part that need to be clarified, the study deserves publication after addressing the following comments:  

Page 1 line 42: Using computer modeling, it can be advantages to evaluate in a patient-specific fashion the interaction of the human tissue with the biomedical devices. In this paper, the screw represents the device so that a computer model could be used to assess the interaction and biomechanical response of living tissue.  Please provide a sentence on this aspect and cite the following paper:

"Rinaudo A, Raffa GM, Scardulla F, Pilato M, Scardulla C, Pasta S. Biomechanical implications of excessive endograft protrusion into the aortic arch after thoracic endovascular repair. Comput Biol Med. 2015 Nov 1;66:235-41."

Page2 line 60: Freezing may impact the biomechanical properties of living tissue. Could you specify why frozen sample were used instead of fresh human tissue?

Page line 65: Please specify if the study was approved by an ethical committee if needed.

page 3 Figure 2: Please evaluate to add a square label to show the region from where the sample was extracted? 

Page 3 line 106: preconditioning of the tissue prior the test is recommended to reduce viscoelastic effect. Please specify if preconditioning was performed for each test. 

Page 3 line 101: How the displacement was measured? In ex-vivo experimental mechanics, digital image correlation is widely used to determine the full-field displacement field and thus the strain. This method is widely adapted and recently applied to in-vivo case as described by Pasta et al.. Please cite the following paper:

"Pasta S, Agnese V, Di Giuseppe M, Gentile G, Raffa GM, Bellavia D, Pilato M. In Vivo Strain Analysis of Dilated Ascending Thoracic Aorta by ECG-Gated CT Angiographic Imaging. Ann Biomed Eng. 2017 Dec;45(12)"

Page 3 line 103: Provide details on the load cell.

Page 4 line 110: Testing should be performed in a saline bath under controlled temperature of 37C. This will mimic the human body behavior. Please explain why a bath was not considered in this study.

page 6 line 221: it is recommended to add a two-three sentences on the study limitation. There were several limitations in the experimental part (ie, missing preconditioning and bath). 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

All comments and suggestions were addressed, though with minimal changes in the text