A Linkage Representation of the Human Hand Skeletal System Using CT Hand Scan Images

Round 1

Reviewer 1 Report

The paper considers a very important topic of identifying the correct linkage representation of the human hand. The findings can be used in various applications such as biomechanic and ergonomic analyses While the paper is generally well written and is worthy of publication, it shows some short backs as outlined below.

General remarks:

The main concern of the paper is rather a short discussion. I think the authors provide enough data and results to be able to provide a sound and extensive discussion. Most of the discussion is short summary of results and a comparison of the results to another researcher. I think, more importance should be made on discussing the results in terms of their interpretation. I suggest authors restructure and rewrite/extend the discussion.

Specific remarks:

“A 256-slice CT scanner (Brilliance 102 iCT; Philips Healthcare, Cleveland, OH, USA) was used to sequentially scan the ten postures while a participant was holding each of the ten postures.” – how did you fixate the hand? What were the scanning times? You mention them later on in the manuscript, however, I think the scanning times should be included in the methods.

“The wrist joint center was estimated as the intersection of the distal wrist crease and the centerline of the third metacarpal [18].” – What is the error of this estimation. Does this have an influence on your results? Why not use your new method? Please elaborate in the manuscript.

Figure 4. – The coordinate system is not aligned according to the text in the manuscript. Z-axis should point directly “out of the paper/screen”. However, you show it tilted. Please correct this or explain in the manuscript.

“Regression models for predicting link lengths based on hand length were established. Regression models for predicting positions of the MCP joint centers of the index, middle, ring, and little fingers and that of the CMC joint center of the thumb were established.” – Please rewrite both sentences. “were established” is repeated and it makes reading monotonous.

Author Response

Thank you for the review on our manuscript. We appreciate your thoughtful comments and suggestions. We have made edits in response to the reviews. Specific responses to each comment are below. Revised portions of the manuscript are highlighted in yellow.

General remarks:

1. The main concern of the paper is rather a short discussion. I think the authors provide enough data and results to be able to provide a sound and extensive discussion. Most of the discussion is short summary of results and a comparison of the results to another researcher. I think, more importance should be made on discussing the results in terms of their interpretation. I suggest authors restructure and rewrite/extend the discussion.

As the reviewer suggested, the discussion section has been restructured and extended.

 

Specific remarks:

1. “A 256-slice CT scanner (Brilliance 102 iCT; Philips Healthcare, Cleveland, OH, USA) was used to sequentially scan the ten postures while a participant was holding each of the ten postures.” – how did you fixate the hand? What were the scanning times? You mention them later on in the manuscript, however, I think the scanning times should be included in the methods.

The dorsal hand of a participant lay on a device individually fabricated by paper clay for each participant to fix the hand of the participant. The information on how to fix the hand and the scanning times has been added.

 

2. “The wrist joint center was estimated as the intersection of the distal wrist crease and the centerline of the third metacarpal [18].” – What is the error of this estimation. Does this have an influence on your results? Why not use your new method? Please elaborate in the manuscript.

The reason that we did not use our proposed method to estimate the wrist joint center was due to the excessive exposure to the ionizing radiation by extra CT scans of the wrist motions. Since we did not estimate the wrist joint center with our proposed method, we could not tell the error of the anatomical estimation and whether it had an influence on our results or not. This limitation of our study has been added in the discussion section.

 

3. Figure 4. – The coordinate system is not aligned according to the text in the manuscript. Z-axis should point directly “out of the paper/screen”. However, you show it tilted. Please correct this or explain in the manuscript.

We added a right angle symbol to the coordinate system to indicate that the z-axis is perpendicular to the xy-plane and pointing to the dorsal direction.

 

4. “Regression models for predicting link lengths based on hand length were established. Regression models for predicting positions of the MCP joint centers of the index, middle, ring, and little fingers and that of the CMC joint center of the thumb were established.” – Please rewrite both sentences. “were established” is repeated and it makes reading monotonous.

Both sentences have been rewritten.

Reviewer 2 Report

This paper proposed a regression method for determining link length and joint center of the hand and fingers. The method is of interest for researchers in ergonomics and can be utilized in the development of digital hand model. The manuscript is also well-written. However, some additional information can improve the quality of the manuscript. My comments are listed below.

1. Why did you use hand breadth or hand length to predict the z-coordinates of the joints center? Considering that hand breath and hang length were used for calculating x-coordinates and y-coordinates respectively, hand parameters in z-direction such as hand thickness should provide better prediction (higher correlation coefficient).
2. Did you validate the regression equations with data other than those used for constructing the regression equations? It is important to understand the accuracy of the equations.
3. As shown in Figure 3, the centroid greatly changes with the change of flexion-extension of the finger. Can you give us information regarding the posture of the finger that correlates to the center of joint rotation proposed in this paper? Did you think that the variations do not have a significant effect on the joint motion during ergonomic analysis?
4. I think that the regression equations are race-specific. It will be difficult to get a good result for European (American) with the regression equations. Do you have a comment on it? Do you think that there is a correlation between hand parameters and body parameters such as height or weight for Asians as well as Europeans (Americans)?

Author Response

Thank you for the review on our manuscript. We appreciate your thoughtful comments and suggestions. We have made edits in response to the reviews. Specific responses to each comment are below. Revised portions of the manuscript are highlighted in yellow.

 

1. Why did you use hand breadth or hand length to predict the z-coordinates of the joints center? Considering that hand breath and hang length were used for calculating x-coordinates and y-coordinates respectively, hand parameters in z-direction such as hand thickness should provide better prediction (higher correlation coefficient).

We built regression models to estimate the z-coordinates of the joint centers based on hand thickness but found that these models have even lower R-squared values and higher standard errors. We have added the related information to the discussion section.

 

2. Did you validate the regression equations with data other than those used for constructing the regression equations? It is important to understand the accuracy of the equations.

We have added one more data different from those used for constructing the regression equations for cross validation of the regression equations.

 

3. As shown in Figure 3, the centroid greatly changes with the change of flexion-extension of the finger. Can you give us information regarding the posture of the finger that correlates to the center of joint rotation proposed in this paper? Did you think that the variations do not have a significant effect on the joint motion during ergonomic analysis?

Finite joint centers change with the change of flexion-extension of the finger. However, the change is quite small (mean distance between finite joint centers = 0.5 to 1.4 mm for different hand joints). For ergonomic analysis, such a small variation might not have a significant effect on the motion of a hand joint during ergonomic analysis. The related information has been added to the discussion section.

 

4. I think that the regression equations are race-specific. It will be difficult to get a good result for European (American) with the regression equations. Do you have a comment on it? Do you think that there is a correlation between hand parameters and body parameters such as height or weight for Asians as well as Europeans (Americans)?

This study was conducted based on Asian hands. To find out whether the regression models in this study are applicable for Caucasians, further studies are needed. This statement has been added to the discussion section. However, this topic is out of scope for the current study.

Reviewer 3 Report

It was a pleasure to review this interesting methodological study, which introduces a new approach for estimating the centers of the CMC and MCP joints, establishing participant-specific linkage representations. Overall, the study’s design and methods seem appropriate and the proposed regression models are comprehensive and very practical to use for future research on hand biomechanical modeling.

I have some minor (yet considerable) recommendations that could likely substantially improve the study’s reliability and clarity. As long as these points are addressed, I would welcome publication of this study:

1. One of the figures is re-used from 2 previously published studies by (most of) the same authors that focused on different hand joints: 1. Yang et al. 2018 (https://doi.org/10.1177/1541931218621154) and 2. Jang et al. 2020 (https://www.mdpi.com/2076-3417/10/24/9129/htm). In fact, the latter 2018 and 2020 previous studies have used multiple identical figures. I would urge the authors to cite the re-used figure (or figures, if others exist) properly in this manuscript. Similarly, a lot of the text seems quite similar (word to word) between the manuscript and the above papers too (which is generally not advisable). Overall, it is crucial that the authors avoid any kind of direct similarities with previously published work, unless this is clarified and properly cited (according to standing publication agreements with each venue and house).
2. Anthropological analyses (and especially paleoanthropological ones focusing on evolutionary hand biomechanics) could greatly benefit from the authors’ calculating approaches. Even though the introduction broadly refers to “anthropometry”, there is no mention to examples of important studies that modeled grasping efficiency in the fossil record (e.g., 1. Feix et al., 2015 Journal Royal Society Interface and 2. Karakostis et al., 2021 Cell Current Biology). I think a discussion of the authors’ method’s applicability in evolutionary hand biomechanics (and the fossil record) would benefit the manuscript and promote its importance.
3. Moreover, it is worth noting that one of the above studies (Karakostis et al., 2021:https://www.cell.com/current-biology/fulltext/S0960-9822(20)31893-5#articleInformation) focusing on the evolution of the hominin thumb relied on calculations of CMC joint torque (as a proxy of efficiency), actually proposing a step-by-step method for assessing the position of CMC joint center (in their models), which showed significant intra- and inter-observer precision (based on a double blind procedure). I would thus suggest to the authors to briefly mention and/or discuss that previous study.
4. The authors relied on 10 different postures representing stages of a certain hand movement (fist closing). Evidently, this is not an exhaustive representation of all possible hand movements. It has to be discussed that future research owes to test how joint center calculations may vary if more diverse grasping patterns were considered in the analysis. This is a crucial piece of information for future applications of this method modeling various grasping patterns.
5. The study seems to be lacking some sort of repeatability test (either intra- or inter-observer) to ensure that the methodology followed was precise and replicable. I would recommend repeating the process for at least one of the participants and assess differences (%) in the calculations of lengths and joint centers.
6. I believe that the regression results should not just show the equations’ standard error but also maximum residual range and 95% intervals, so as to provide a complete view of maximum potential error in joint center calculation. Considering the variability of the human hand’s form, this is both important and interesting for future studies.
7. There are certain identical sentences in the text, e.g., first sentence of Discussion and Conclusions.

 

Author Response

Thank you for the review on our manuscript. We appreciate your thoughtful comments and suggestions. We have made edits in response to the reviews. Specific responses to each comment are below. Revised portions of the manuscript are highlighted in yellow.

 

1. One of the figures is re-used from 2 previously published studies by (most of) the same authors that focused on different hand joints: 1. Yang et al. 2018 (https://doi.org/10.1177/1541931218621154) and 2. Jang et al. 2020 (https://www.mdpi.com/2076-3417/10/24/9129/htm). In fact, the latter 2018 and 2020 previous studies have used multiple identical figures. I would urge the authors to cite the re-used figure (or figures, if others exist) properly in this manuscript. Similarly, a lot of the text seems quite similar (word to word) between the manuscript and the above papers too (which is generally not advisable). Overall, it is crucial that the authors avoid any kind of direct similarities with previously published work, unless this is clarified and properly cited (according to standing publication agreements with each venue and house).

As the reviewer suggested, the similar figure and contents have been cited or modified.

 

2. Anthropological analyses (and especially paleoanthropological ones focusing on evolutionary hand biomechanics) could greatly benefit from the authors’ calculating approaches. Even though the introduction broadly refers to “anthropometry”, there is no mention to examples of important studies that modeled grasping efficiency in the fossil record (e.g., 1. Feix et al., 2015 Journal Royal Society Interface and 2. Karakostis et al., 2021 Cell Current Biology). I think a discussion of the authors’ method’s applicability in evolutionary hand biomechanics (and the fossil record) would benefit the manuscript and promote its importance.

According to the comments of the reviewer, a discussion of the application of the proposed method in evolutionary hand biomechanics (and the fossil record) including the two papers has been added.

 

3. Moreover, it is worth noting that one of the above studies (Karakostis et al., 2021:https://www.cell.com/current-biology/fulltext/S0960-9822(20)31893-5#articleInformation) focusing on the evolution of the hominin thumb relied on calculations of CMC joint torque (as a proxy of efficiency), actually proposing a step-by-step method for assessing the position of CMC joint center (in their models), which showed significant intra- and inter-observer precision (based on a double blind procedure). I would thus suggest to the authors to briefly mention and/or discuss that previous study.

As suggested by the reviewer, Karakostis et al.’s study has been mentioned and discussed.

 

4. The authors relied on 10 different postures representing stages of a certain hand movement (fist closing). Evidently, this is not an exhaustive representation of all possible hand movements. It has to be discussed that future research owes to test how joint center calculations may vary if more diverse grasping patterns were considered in the analysis. This is a crucial piece of information for future applications of this method modeling various grasping patterns.

The inclusion of more diverse grasping patterns in the future research has been added to the discussion section.

 

5. The study seems to be lacking some sort of repeatability test (either intra- or inter-observer) to ensure that the methodology followed was precise and replicable. I would recommend repeating the process for at least one of the participants and assess differences (%) in the calculations of lengths and joint centers.

As the reviewer suggested, repeatability test (intra- and inter-observers) for one participant has been added.

 

6. I believe that the regression results should not just show the equations’ standard error but also maximum residual range and 95% intervals, so as to provide a complete view of maximum potential error in joint center calculation. Considering the variability of the human hand’s form, this is both important and interesting for future studies.

As the reviewer suggested, maximum residual range and 95% confidence intervals have been added.

 

7. There are certain identical sentences in the text, e.g., first sentence of Discussion and Conclusions.

Identical sentences in the text have been revised.

Round 2

Reviewer 1 Report

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Reviewer 2 Report

Thank you for your response. This study is very interesting. The manuscript can be accepted now.