Design and Development of Magnesium-Based Suture Anchor for Rotator Cuff Repair Using Finite Element Analysis and In Vitro Testing

Round 1

Reviewer 1 Report

Recommendation: Accept with minor revision

 

Minor suggestions:

• Figure 2 provides no information about the type of suture anchors in the figure and if they are preferred/ used specifically for shoulder/hip/another part. Please label/name the each anchor in the figure and mention a line about where they might be best used in the figure legend. If they can all be applied to various parts, please mention so.
• Mention 2-3 lines each about FEA and ASTM F-43 tests in the introduction with recent references.
• Along with other parameters, there is Poisson’s ratio mentioned in Table 1. However, it ha not been mentioned anywhere else in the text. What is it’s significance? Why is it important to consider Poisson’s ratio and what value is it adding to your table? Please include in your text.
• Please add the figure number in your results that refer to the data/graph/table for that section of results. It is currently unclear, which figure is for which section of the results. For example please add “(Figure 10)” when describing your results for results section 3.5
• Please add another 3-4 lines describing your results for section 3.5
• Please provide/ refer to the evidence for your conclusion. It is unclear which figure/table should be referred to for each section of your result.

Author Response

1. Thank you for this reminder! We've modified the figure 2 and also specified the different materials of each suture anchors and the parts they can be applied to in figure 2. This figure is mentioned in the line 82-85 .
2. The introduction with recent references are added in lines 50-59. "To validate the primary stability of a suture anchor’s fixation, studies have used finite element analysis (FEA) for diverse purposes, including the mechanical analysis of soft tissue and bone implants design [11,12]. With FEA, designers are able to predict whether their design are suitable for clinical use and further revise the design if they discover any problems. After the suture anchor is manufactured, the axial pullout test, following the standard operating procedure of ASTM-F543, executed during the removal of bone screws from their insertion site in bone blocks is a standard approach for quantifying the primary stability of designs [13,14]. Several studies has not only used the testing procedure of ASTM F543 for design analysis, but also used it to study the local deformation of bone structure during a screw pullout test [15]."

3. The Poisson’s ratio is a measure of the Poisson effect, the deformation of a material in directions perpendicular to the specific direction of loading.  It will influence the stress and strain results of finite element analyses. The Poisson's ratios of the Mg-based alloy and bone blocks are variable and adjustable because they are new or PU foam. To simplify this study by numerical simulation, commonly used properties of Mg alloy and PU foams in references 28 & 29 were applied to our models. The Poisson's ratio is one of the limitations of this study. It is one of possible reasons resulting in deviation between results of FEA and mechanical testing. The real Poisson’s ratio caused by anisotropy of materials might be investigated in advanced studies in the future. The related explanation was added in lines 316 and 319 of the discussion.

4. We've added the figure number for the reference in introduction, methods and results of the manuscript. Sorry for these mistakes!
5. Please check line 246-248. " According to results of FEA simulation, the design with the parameter LA1UP2W1TA3, with a larger tapered angle (TA), a smaller upper thread pitch (UP), a smaller groove width (W), and a smaller lower thread angle (LA), had the highest pullout strength in normal bone blocks. With an outer radius of 2.5 mm, the prototype of this optimal anchor was chosen to be manufactured and tested in the material testing machine."

6. We've added the figure and table number for the reference in the conclusion section.

Reviewer 2 Report

The article titled 'Design and Development of Magnesium-Based Suture Anchor for Rotator Cuff Repair Using Finite Element Analysis and In Vitro Testing' presents testing of a new anchor. The study seems to be in pilot phase and limited data is presented. My specific comments are as follows:

1. Four factor full factorial design was mentioned in line 79 but it was not clear which factors were manipulated and analyzed. Please specify the factors. Why only six samples were generated from factorial design?
2. Line 115-116 mentions about Mg alloy. What is the source and composition of this alloy? How it was obtained (in house or procured?).
3. None of the figures were mentioned in the text. It is not clear where they belong. Fig 4 legend mentions a and b parts, but it was not shown in the actual figure. 
4. The fig 10 shows some data of samples 1-6. However, those samples were not mentioned in the text. Does names like LA1UP2W2TA3 correspond to any samples?
5. Please explain why a control was not used for the study. How can you compare this new material with commercially available materials?

 

Author Response

1. Thank you for your comments. Four factor full factorial was conducted in this simulation study, which we specified our four factors in figure 3. Twenty-four samples were tested in FEA and we generated the data in section 3.1-3.4 (line 181-243). The number of the optimal anchor with the parameter LA1UP2W1TA3 prototyped was six. The pullout strength of six anchors were averaged for comparison between normal and osteoporotic bone blocks.
2. Previously determined linear elastic properties of a common magnesium alloy (AM 1004-T61) were applied to the FE models of suture anchors. This Mg alloy's properties referred to data listed in the textbook (the Mechanics of Materials by R.C. Hibbeler, 9th edition, page 863). This reference was added.

3. We've corrected it. Please see line 147-148.

4. The sample with parameter LA1UP2W1TA3 was chosen to be manufactured, which we've added to line 206. The reason for choosing this combination of parameters are that this optimal design had the highest pullout strength in FEA test, and six specimens with this design were tested and compared in two groups of bone blocks.

5. The main purpose of this study was to assess the effects of various combinations of distinctive parameters through FEA.The pullout test was to validate the result of finite element analysis. The results showed that the pullout strength of FEA and pullout test has the same ratio between 10 and 20 PCF group, which was about 1:4, although there was ignorable deviation between pullout strengths measured in two methods. For two testing methods, the strength in the osteoporotic bone was compared with testing in normal bone as the control group. The conclusion found by parametrical investigation of our FE modeling optimized the design of the anchor in its clinical application. Before this parametrical investigation, we have compared two commercially available anchors made of Titanium and biocomposite materials in our previous study. If conflict of interests were excluded, those data might be useful for comparison among anchors made of different materials in the future.

Reviewer 3 Report

1. The figures in the manuscript are not referenced in the text making them hard to understand. In particular, Figure 2 seems to have no explanation.
2. The title of the manuscript suggests it will investigate a Magnesium-Based Suture Anchor, however the appeal of using such a material is only minimally explained at the end of the manuscript.
3. The authors extensively discuss the In Vitro model they are using in the manuscript. While they do provide references to the model, It would be useful if more specifics of the model system were explained, particularly because they have unreferenced figures showing the setup.

Author Response

1. Thank you for this reminder! We've modified the figure 2 and also specified the different materials of each suture anchors and the parts they can be applied to. All figures have been mentioned in the text.

2. We've added more description about the new material and mentioned the use of mg alloy in bone screw implant in the introduction and the methods, please check line 74-80 and 157-159.

3. We added the explanation at line 171 to 174, " The test block was stabilized by the clamp, which was fixed to the base. The suture anchor with the suture applied on was inserted into the test block. The suture then was fixed to the testing machine to provide the axial force for pullout." The setup was based on the reference 34.

Round 2

Reviewer 2 Report

The manuscript improved by including more results in the revised version. Since line numbers are removed in the revised manuscript, it was difficult to find where the corrections were made. Few critical elements were answered by the authors but not included in the revised manuscript (for example, justification of not including another metal alloy as control). Please include the answers in the revised manuscript.

 My specific comments are as follows:

Table 2 and 3: Please be consistent with the legends (pullout strength vs reaction force). Also, please clarify the first row for these tables. The first row currently shows numbers only.

Figures 9-11: Scale of Y axis for a and b parts should be same.

 

Author Response

1. We have highlighted the last and new modified parts by yellow in the document. We apologize for the inconvenience of reviewing the previous one. In the last 3^rd paragraph of the discussion, we have explained that this parametric investigation of FEA compared the results in osteoporotic models with the control group in normal bone models. Regarding comparison with materials frequently used in conventional products, further studies have to be conducted to understand the effect of materials. This was included in the discussion. Thank you for your comments!   2. we clarified the first row of the tables from table 2 to table 9, replace the numbers with "small", "medium" and "large" respectively. It will be clearer to understand the difference in design parameters among models.   3. We let the scale of the y axis of the figures, from figure 9 to 12, to be the same. In addition, we removed figure 2 due to consideration of its copyright.

Reviewer 3 Report

The changes made have helped clarify the manuscript.

Author Response

Thank you for your valuable comments and suggestion on our manuscript!