Effects of Achilles Tendon Moment Arm Length on Insertional Achilles Tendinopathy
, Tomohiro Matsui 3, Hiroaki Kurokawa 1, Akira Taniguchi 1, Tsukasa Kumai 4 and Yasuhito Tanaka 1Round 1
Reviewer 1 Report
The authors present a newly and simple mechanical evaluation method for the diagnostics and possible treatment of IAT in combination with a designated surgery technique. The usage of X-ray is a simple method and allows to perform anatomical calculations easily. This also is the biggest weakness of that study. The conclusions are based on a 2D model. Since the AT insertion is a 3D entity (surface, not line), the assumptions have to be interpreted rather as possible biomechanical suggestions than definite predictions. Performing 3D analyses eg. with 3D MRI allows more precise analyses and should be the gold standard. Under the aspect of clinical relevance and applicability, this should be discussed, references and explained extensively in the limitations section in order to be accepted.
Another lacking information is the general surgery success, indicated by objective and subjective data.
In general, this should be performed on a bigger study population, with proper statistical analysis, in order to substantiate the hypothesis.
Taking into account these considerations, and after a major revision, this manuscript could be accepted as a short communication or case study, rather than an article.
Please find my detailed comments/recommendations below:
37-38: Sugg: refer to Fig. 1
62-63 and 75-79: A simple graphic of the surgery technique will contribute to understanding. Also an interesting question is – how much of the insertional area/thickness was excised. Assuming L = 17 cm, the postoperative results suggest an excision of almost 1 cm. Can you please provide more surgical details and add an X-ray of the same patient pre- and post surgery to make it more comprehensible.
70-71 and 80-81: The inclusion criteria and time points are inconclusive. There is no data on the postoperative outcome, neither subjectively, not objectively after one year. The purpose of the MRIs is unclear.
72-74 Syntax confusing
75: “The reconstruction in all cases”: also in the control group?
85-87: Based on which anatomic-biomechanical consideration was L - the foot length chosen? Also: “foot length” is a confusing term since the foot length is a defined term (heel to toe) for shoe sizes.
82+94: Did you xray both feet?
99: Consider using “body weight” instead of “weight”.
103, results and 176-177: The paired t-test is designated for paired analysis. For comparing both study groups you should use the unpaired t-test. Also – did you check for Gaussian distribution, respectively? Your standard deviations suggest a non-Gaussian distribution. I would recommend to see statistical council.
80-81 and 114-115: methods state, that the purpose was to examine the extent of the expansion of the Achilles tendon insertion area. There are no shown results regarding the insertion area.
Figure 4: Is that the same patient? Here two different sections were used (sagittal geometry of calcaneus is different). Also, the bedding of the patient must have been different (tibio-calcaneal shift: preoperatively calf must have been supported from below, postoperatively the calcaneus was propped, causing a dorsalisation of the tibia). The comparison of the two images is biased. Also the figure legend lacks basic information.
123-124: Even though the calculations from linear geometry are correct, the results are to be interpreted cautiously. The insertion is a surface, not a line, and there is no information about the third dimension at all. Findings from these calculations cannot be generalize to the insertion. MRI 3D models pre- and post-surgery should be used.
Table 1: foot or feet? Also distribution of feet in study groups unclear regarding sex. Mind significant digits.
Figure 5 needs clarification in the first graphic (use a,b,c for the three graphs): I suppose that was pre-operatively? Mind consistent capitalisation.
199-201 and 206-207: based on the comments before, this conclusion cannot be drawn from the data shown in that study, since the study did not investigate the area of the insertion. This and the general limitation of a 2D imaging technique.
222-223: This general and hard conclusion cannot be drawn based on a sample of n=10 (8 patients). The development of IAT underlies many factors, that are independent from pure anatomy.
Author Response
Prof. Dr. Takayoshi Kobayashi
Editor-in-Chief
Applied Sciences: New Trends in Sport and Exercise Medicine
- 09. 2020
Dear Ms. Alice Gou
re: “Effects of Achilles tendon moment arm length on insertional Achilles
tendinopathy.”; Manuscript ID: applsci-922968
We are most grateful to you and the reviewers for their helpful comments on the original version of our manuscript. We have revised our paper following the reviewer’s comments. Below is the point by point responses to the comments.
Review 1
Comments and Suggestions for Authors
The authors present a newly and simple mechanical evaluation method for the diagnostics and possible treatment of IAT in combination with a designated surgery technique. The usage of X-ray is a simple method and allows to perform anatomical calculations easily. This also is the biggest weakness of that study. The conclusions are based on a 2D model. Since the AT insertion is a 3D entity (surface, not line), the assumptions have to be interpreted rather as possible biomechanical suggestions than definite predictions. Performing 3D analyses eg. with 3D MRI allows more precise analyses and should be the gold standard. Under the aspect of clinical relevance and applicability, this should be discussed, references and explained extensively in the limitations section in order to be accepted.
Answer: We are grateful to Reviewer 1 for your critical comments. These suggestions from your view were very helpful for us. We are sure our manuscript will be further improved by incorporating them. We agree with the reviewer that the 2D model is a weakness of the X-ray method. As you suggested, the Achilles tendon insertion is surface, so I also think it is better to evaluate with 3D MRI instead of 2D. We wanted to show that this study can be evaluated by a simple method that can be used daily in clinics. Also, we wanted to evaluate the weighted position, which is not easy in MRI imaging. Therefore, we evaluated it by the weight-bearing X-ray. However, the fact that 3D evaluation is not performed is a big limitation, and I added this to the limitation section. (Lines 246-249)
Another lacking information is the general surgery success, indicated by objective and subjective data.
Answer: Thank you for your advice. We have added AOFAS scale and post-operative MRI findings as objective data and VAS as subjective evaluation. In all cases, the AOFAS scale and VAS improved, and MRI findings showed disappearance abnormal signal in the tendon. (Lines 123-129)
In general, this should be performed on a bigger study population, with proper statistical analysis, in order to substantiate the hypothesis.
Answer: We agree with the reviewer that the number of cases was small. If the number of cases is large and proper statistical analysis can be performed, I think that a better evaluation will be possible. Since the number of samples was small this time, we evaluated it by a comparative study between the two groups. This is a limitation of our study, and I added this to the limitation section. (Lines 244-245)
Taking into account these considerations, and after a major revision, this manuscript could be accepted as a short communication or case study, rather than an article.
Answer: As you suggested, this paper may be more suitable for a short communication or case study.
Please find my detailed comments/recommendations below:
37-38: Sugg: refer to Fig. 1
Answer: Thank you for your advice. We have added a new Figure about the contraction of the triceps surae.
62-63 and 75-79: A simple graphic of the surgery technique will contribute to understanding. Also an interesting question is – how much of the insertional area/thickness was excised. Assuming L = 17 cm, the postoperative results suggest an excision of almost 1 cm. Can you please provide more surgical details and add an X-ray of the same patient pre- and post surgery to make it more comprehensible.
Answer: Thank you for your advice. As you suggested, the moment arm changes about 7 mm before and after surgery. I think this is an important change. We have added a new Figure about the surgical technique and an X-ray of the same patient pre- and post-surgery.
70-71 and 80-81: The inclusion criteria and time points are inconclusive. There is no data on the postoperative outcome, neither subjectively, not objectively after one year. The purpose of the MRIs is unclear.
Answer: The IAT group subject is an individual who has undergone surgical treatment for IAT at our hospital between 2014 and 2019. We excluded individuals with a history of collagen diseases or trauma other than the Achilles tendon injuries, and those who could not be followed up for more than one year after surgery. The control group subject is made up of patients with no complaints of the ankle joint nor history of surgical trauma. The postoperative data was obtained 1 year after surgery. We have added AOFAS scale and post-operative MRI findings as objective data and VAS as subjective evaluation. The purpose of the MRIs is to evaluate the morphology of the Achilles tendon insertion. I added this information to the revised manuscript. (Lines 123-129)
72-74 Syntax confusing
Answer: As you suggested, we have revised the sentence accordingly.
75: “The reconstruction in all cases”: also in the control group?
Answer: I apologize for making a misleading statement. Reconstruction was performed only for the IAT group.
85-87: Based on which anatomic-biomechanical consideration was L - the foot length chosen? Also: “foot length” is a confusing term since the foot length is a defined term (heel to toe) for shoe sizes.
Answer: We changed the term “the foot length” to “the length of the sole”.
82+94: Did you xray both feet?
Answer: I apologize for making a misleading statement. The images of the affected side were taken for patients in the IAT group, while those of the healthy side were taken for patients in the control group.
99: Consider using “body weight” instead of “weight”.
Answer: As you suggested, we have changed “body weight”.
103, results and 176-177: The paired t-test is designated for paired analysis. For comparing both study groups you should use the unpaired t-test. Also – did you check for Gaussian distribution, respectively? Your standard deviations suggest a non-Gaussian distribution. I would recommend to see statistical council.
Answer: I apologize for my mistake. We already used the unpaired t-test. This is a mistake in writing. Therefore, the result of statistics does not change. Also, I checked for Gaussian distribution. As you suggested, our data is a non-Gaussian distribution.
80-81 and 114-115: methods state, that the purpose was to examine the extent of the expansion of the Achilles tendon insertion area. There are no shown results regarding the insertion area.
Answer: As you suggested, we did not examine the extent of the expansion of the Achilles tendon insertion area. We performed MRI to evaluate the morphology of the Achilles tendon insertion; this revealed Achilles tendon insertion running from the proximal knotless anchor insert to the distal knotless anchor insert via the suture bridge technique. I have included this information in the manuscript. (Lines 126-129)
Figure 4: Is that the same patient? Here two different sections were used (sagittal geometry of calcaneus is different). Also, the bedding of the patient must have been different (tibio-calcaneal shift: preoperatively calf must have been supported from below, postoperatively the calcaneus was propped, causing a dorsalisation of the tibia). The comparison of the two images is biased. Also, the figure legend lacks basic information.
Answer: These are the same patients. However, as you suggested, we changed to a more understandable image and added a description.
123-124: Even though the calculations from linear geometry are correct, the results are to be interpreted cautiously. The insertion is a surface, not a line, and there is no information about the third dimension at all. Findings from these calculations cannot be generalize to the insertion. MRI 3D models pre- and post-surgery should be used.
Answer: We agree with the reviewer that the 2D model is a weakness of the X-ray method. As you suggested, the Achilles tendon insertion is surface, so I also think it is better to evaluate with 3D MRI instead of 2D. We wanted to show that this study can be evaluated by a simple method that can be used in daily clinics. Also, we wanted to evaluate the weighted position, which is not easy in MRI imaging. Therefore, we evaluated it by the weight-bearing X-ray. However, the fact that 3D evaluation is not performed is a big limitation, and I added this to the limitation section. (Lines 246-249)
Table 1: foot or feet? Also distribution of feet in study groups unclear regarding sex. Mind significant digits.
Answer: The images of the affected side were taken for patients in the IAT group, while those of the healthy side were taken for patients in the control group. Hence, “foot” refers to 4 males and 4 females in the IAT groups and 8 males and 7 females in the Control group. As you suggested, I have corrected this error. Kindly check and let me know if you feel this is correct. (Lines 89-91)
Figure 5 needs clarification in the first graphic (use a,b,c for the three graphs): I suppose that was pre-operatively? Mind consistent capitalisation.
Answer: Thank you for pointing this out. As you suggested, that was pre-operatively. We fixed and have added a description accordingly.
199-201 and 206-207: based on the comments before, this conclusion cannot be drawn from the data shown in that study, since the study did not investigate the area of the insertion. This and the general limitation of a 2D imaging technique.
Answer: As you suggested, we have added the limitation of a 2D imaging technique.　I have changed the expression regarding the expansion of the area because it was overstated. Although the study did not investigate the area of the insertion, we confirmed on MRI that the Achilles tendon insertion ran from the proximal knotless anchor insert to the distal knotless anchor insert via the suture bridge technique. Also, we investigated the central axis of the Achilles tendon. Therefore, we corrected the text.
222-223: This general and hard conclusion cannot be drawn based on a sample of n=10 (8 patients). The development of IAT underlies many factors, that are independent from pure anatomy.
Answer: We agree with the reviewer that the development of IAT underlies many factors. A long moment arm may be one of the causes of IAT. We corrected the text because it was overstated.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Overall Comments:
Thank you for your interesting manuscript.
The language of the manuscript needs to be revised as there are some major grammatical mistakes (e.g. Line 14...it is unknown should be expressed as „is unknown“, see further examples below).
M&Ms:
The section with the description of measurement performance on plain x-ray images is a bit difficult to read. Maybe it would be good, to add another Figure, explaining the first set lines, followed by another Figure explaining additional measurements.
Line 103 ff.: Statistical tests were performed the paired student.... This is grammatically incorrect. Please correct.
Which was your CI for the level of significancy?
Results
Line 117: You state that there were no significant differences in the alpha angle between control and IAT group. Therefore, I would suggest to delete the corresponding p<0.05 symbol from the corresponding image in Figure 5. It confuses the reader.
Line 119: ..showing significant differences“ without the
Line 121 ff: The force applied tot he tendon was first 166.2 kg in the IAT group postoperatively, and then 200.8 kg in the IAT group postoperatively, what is correct? Please explain.
Discussion:
Major grammatical mistakes again, needs language revision.
If the COR and TE methods are mainly used for this measurement, I’d recommend to mention it in the introduction too.
Line 160 ff: Who determined, that weight-bearing X-ray is the most suitable method? Please add a reference.
„In addition, Manja et al. [10] showed that the moment arm length and α angle are influenced by the difference in the shape of the foot, such as flat and concave feet. In the present study, no significant 
difference in α angle between the control and experimental groups was observed, indicating that the results are not influenced by the difference in the shape of the subject’s foot, even in flat and concave feet.“ => How can you conclude, that the missing differences in the alpha angle between your control group and the IAT group suggest, that the foot’s shape doesn’t have any influence, when you didn’t compare subgroups with flat or concave feet? Can you explain please, as Manja et al. obviously compared these two subgroups and concluded it therefrom. I think you might only conclude, that different food shapes wouldn’t have any influence on the moment arm length of healthy and IAT individuals, which you actually measured. Or that the food shape pre- and postoperatively didn’t vary so that no differences of angles were expected anyways between the IAT subgroups.
Line 192: is shown tob e...
Line 202 ff: So, if there was a significant difference between the force of healthy and operated patients with IAT, who showed a higher applied force, why would it be good to follow an operation method, which increases this force and causes IAT, if the moment arm length couldn’t be reduced adequatly?
Figures overall:
Well chosen images.
I’d recommend to not only describe the measurements made on the images in the corresponding legends, but also to shortly explain, what the interpretation of the measurements is in each Figure.
Figure 1:
Caption: Line 2 it should be plantar axis, not planter. And I don’t understand the last sentence/part of the legend.
Figure 2:
a and b should be explained as well.
Between Figure 3 and 4 there is a sentence included, please add this paragraph („We calculated..:“) to the corresponding section.
Figure 4:
Rewrite the legend, describe what is seen and what is marked with the yellow arrows.
Figure 5:
Please give more details about what is seen on the different parts. I’d recommend to rename the single parts of Figure 5 with letters (a,b,c...).
And it is „operative“ not „oparative“, please change the texts in the figures correspondingly.
References:
Add publications of Frankewycz B et al. for sections which focus on elastic properties and their influence on the AT (e.g. Line 192f).
Author Response
Prof. Dr. Takayoshi Kobayashi
Editor-in-Chief
Applied Sciences: New Trends in Sport and Exercise Medicine
- 09. 2020
Dear Ms. Alice Gou
re: “Effects of Achilles tendon moment arm length on insertional Achilles
tendinopathy.”; Manuscript ID: applsci-922968
We are most grateful to you and the reviewers for their helpful comments on the original version of our manuscript. We have revised our paper following the reviewer’s comments. Below is the point by point responses to the comments.
Review 2
Comments and Suggestions for Authors
Overall Comments:
Thank you for your interesting manuscript.
The language of the manuscript needs to be revised as there are some major grammatical mistakes (e.g. Line 14...it is unknown should be expressed as „is unknown“, see further examples below).
We are grateful to Reviewer 2 for the critical comments and useful suggestions that have helped us to improve our paper considerably. As indicated in the responses that follow, we have revised our paper following these comments.
M&Ms:
The section with the description of measurement performance on plain x-ray images is a bit difficult to read. Maybe it would be good, to add another Figure, explaining the first set lines, followed by another Figure explaining additional measurements.
Answer: Thank you for your advice. As you suggested, we have added a new figure.
Line 103 ff.: Statistical tests were performed the paired student.... This is grammatically incorrect. Please correct.
Answer: As you suggested, we corrected it accordingly.
Which was your CI for the level of significancy?
Answer: We used 95%CI. Therefore, we corrected it accordingly.
Results
Line 117: You state that there were no significant differences in the alpha angle between control and IAT group. Therefore, I would suggest to delete the corresponding p<0.05 symbol from the corresponding image in Figure 5. It confuses the reader.
Answer: As you suggested, we corrected it.
Line 119: ..showing significant differences“ without the
Answer: As you suggested, we corrected it.
Line 121 ff: The force applied tot he tendon was first 166.2 kg in the IAT group postoperatively, and then 200.8 kg in the IAT group postoperatively, what is correct? Please explain.
Answer: I apologize for my mistake. This is a mistake in writing; 166.2 kg was applied in the IAT group preoperatively and 200.8 kg was applied in the IAT group postoperatively.
Discussion:
Major grammatical mistakes again, needs language revision.
If the COR and TE methods are mainly used for this measurement, I’d recommend to mention it in the introduction too.
Answer: As you suggested, we have added the introduction.
Line 160 ff: Who determined, that weight-bearing X-ray is the most suitable method? Please add a reference.
Answer: The usage of X-ray is a simple method and allows to perform anatomical calculations easily. Therefore, we determined that it was a good method in our study, but not in all studies. Most references were made to Manja's research.
„In addition, Manja et al. [10] showed that the moment arm length and α angle are influenced by the difference in the shape of the foot, such as flat and concave feet. In the present study, no significant 
difference in α angle between the control and experimental groups was observed, indicating that the results are not influenced by the difference in the shape of the subject’s foot, even in flat and concave feet.“ => How can you conclude, that the missing differences in the alpha angle between your control group and the IAT group suggest, that the foot’s shape doesn’t have any influence, when you didn’t compare subgroups with flat or concave feet? Can you explain please, as Manja et al. obviously compared these two subgroups and concluded it therefrom. I think you might only conclude, that different food shapes wouldn’t have any influence on the moment arm length of healthy and IAT individuals, which you actually measured. Or that the food shape pre- and postoperatively didn’t vary so that no differences of angles were expected anyways between the IAT subgroups.
Answer: I apologize for making a misleading statement. I have never thought the foot’s shape does not have any influence. What I would like to say is that since there was no significant difference in α angle, the significant difference of this data might not be due to the effect of foot shape, but only due to the presence or absence of IAT. Manja et al. said that the average α angle was statistically different from foot type, and Achilles tendon moment arm for pes cavus than for pes planus. In other words, the fact that there is no significant difference in the α angle means that there is no significant difference in the shape of the foot. Also, different foot shapes affect the length of the Achilles tendon moment. In our study, there was no significant difference in α angle between the control and IAT groups. Therefore, it might not be necessary to consider the difference in foot shape.　However, the number of cases was small. The study needs to proceed with an increased number of cases.
Line 192: is shown tob e...
Answer: As you suggested, we have corrected accordingly.
Line 202 ff: So, if there was a significant difference between the force of healthy and operated patients with IAT, who showed a higher applied force, why would it be good to follow an operation method, which increases this force and causes IAT, if the moment arm length couldn’t be reduced adequatly?
Answer: Although this study cannot consider expanding the area, because it may reduce the energy per unit area by further increasing the area of the insertion of the Achilles tendon. There are also other influences and factors. The development of IAT underlies many factors. Although the power became stronger, the reason why this surgery is good is that the area of ​​the insertion area expanded or the area shape changed, but this study could not be evaluated in 3D, so this was set as the limitation.
Figures overall:
Well chosen images.
I’d recommend to not only describe the measurements made on the images in the corresponding legends, but also to shortly explain, what the interpretation of the measurements is in each Figure.
Answer: As you suggested, we have added explanatory text accordingly.
Figure 1:
Caption: Line 2 it should be plantar axis, not planter. And I don’t understand the last sentence/part of the legend.
Answer: As you suggested, we corrected, and we have added explanatory text. (Lines 155-158)
Figure 2:
a and b should be explained as well.
Answer: As you suggested, we have explained a and b accordingly.
Between Figure 3 and 4 there is a sentence included, please add this paragraph („We calculated..:“) to the corresponding section.
Answer: As you suggested, we fixed it.
Figure 4:
Rewrite the legend, describe what is seen and what is marked with the yellow arrows.
Answer: As you suggested, we have added explanatory text. (Lines 170-173)
Figure 5:
Please give more details about what is seen on the different parts. I’d recommend to rename the single parts of Figure 5 with letters (a,b,c...).
And it is „operative“ not „oparative“, please change the texts in the figures correspondingly.
Answer: As you suggested, we have added explanatory text.
References:
Add publications of Frankewycz B et al. for sections which focus on elastic properties and their influence on the AT (e.g. Line 192f).
Answer: We added the reference that you suggested. (Lines 346-348)
Author Response File: Author Response.docx
Reviewer 3 Report
- there are many different causes of insertional Achilles tendinopathy. A long moment arm is one of them, not exclusive.
- in literature several surgical techniques even without moment arm reduction are reported with good results
- in this study clinical results are not reported
- the authors coiuld add a comment on the Haglund deformity manageable above the insertional area with potential influences on the Achilles moment arm.
Author Response
Prof. Dr. Takayoshi Kobayashi
Editor-in-Chief
Applied Sciences: New Trends in Sport and Exercise Medicine
- 09. 2020
Dear Ms. Alice Gou
re: “Effects of Achilles tendon moment arm length on insertional Achilles
tendinopathy.”; Manuscript ID: applsci-922968
We are most grateful to you and the reviewers for their helpful comments on the original version of our manuscript. We have revised our paper following the reviewer’s comments. Below is the point by point responses to the comments.
Review 3
Comments and Suggestions for Authors
1. there are many different causes of insertional Achilles tendinopathy. A long moment arm is one of them, not exclusive.
Answer: We are grateful to Reviewer 3 for the critical comments and useful suggestions that have helped us to improve our paper considerably. We agree with the reviewer that there are many different causes of insertional Achilles tendinopathy and a long moment arm is one of them. I have changed the expression because it was overstated. This study revealed the relationship between the IAT and the Achilles tendon moment. This is a new discovery.
2. in literature several surgical techniques even without moment arm reduction are reported with good results
Answer: As you suggested, several surgical techniques, even without moment arm reduction, is a good result. Because the development of IAT underlies many factors, it is possible to treat other than adjusting the moment arm. This study evaluated the changes before and after the surgery and discussed how much the moment arm is changing.
3. in this study clinical results are not reported
Answer: As you suggested, we have added the AOFAS scale and post-operative MRI findings as objective data and VAS as subjective evaluation. (Lines 124-126)
4. the authors coiuld add a comment on the Haglund deformity manageable above the insertional area with potential influences on the Achilles moment arm.
Answer: As you suggested, we removed the Haglund deformity in our surgical technique; hence, Achilles tendon insertion can extend forward. Regarding this, I added a picture in the surgical method to make it easier to understand. I think that it might not be significant preoperatively. The Haglund deformity causes retrocalcaneal bursitis. The main pathology of retrocalcaneal bursitis is compression damage. On the other hand, the main pathology of Insertional Achilles tendinopathy is tracking damage. Also, the Achilles moment arm affected tracking damage. To avoid confusion, I did not mention the Haglund deformity for preoperative IAT this time.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
most of the comments were taken into account.
