List of Papers By topics Author List
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Authors
Wenzhangzhi Guo, Ty Trusty, Joel C. Davies, Vito Forte, Eitan Grinspun, Lueder A. Kahrs
Abstract
Skin flap is a common technique used by surgeons to close the wound after the resection of a lesion. Careful planning of a skin flap procedure is essential for the most optimal functional and aesthetic outcome. However, currently surgical planning is mostly done based on surgeons’ experience and preferences. In this paper, we introduce a finite element method (FEM) simulation that is used to make objective recommendations of the most optimal flap orientation. Rhomboid flap is chosen as the main flap type of interest because it is a very versatile flap. We focus on evaluating suture forces required to close a wound as large tension around it could lead to complications. We model the skin as an anisotropic material where we use a single direction to represent the course of relaxed skin tension lines (RSTLs). We conduct a thorough search by rotating the rhomboid flap in small increments (1°-10°) and find the orientation that minimizes the suture force. We repeat the setup with different material properties and the recommendation is compared with textbook knowledge. Our simulation is validated with minimal error in comparison with other existing simulations. Our simulation shows to minimize suture force, the existing textbook knowledge recommendation needs to be further rotated by 15°-20°.
Link to paper
DOI: https://doi.org/10.1007/978-3-031-43996-4_55
SharedIt: https://rdcu.be/dnwPZ
Link to the code repository
N/A
Link to the dataset(s)
N/A
Reviews
Review #1
- Please describe the contribution of the paper
The study focuses on construction of computational biomechanics models using finite element method and conducting simulations using these models to provide recommendations for aligning rhomboid flaps relative to Relaxed Skin Tension Lines RSTLs based on the predicted suture force. The results are verified against the simulations conducted using other established methods and against the textbook knowledge.
- Please list the main strengths of the paper; you should write about a novel formulation, an original way to use data, demonstration of clinical feasibility, a novel application, a particularly strong evaluation, or anything else that is a strong aspect of this work. Please provide details, for instance, if a method is novel, explain what aspect is novel and why this is interesting.
Quantitative comparison with the results obtained using other estbalished modellimg and simulation methods the Authors regard as state-of-the-art is included. Hausdorff distance between the predicted suture lines is a very relevant measure of difference between the results obtained using the two simulation/modelling methods used in the study.
The study aims at providing clinically relevant results by providing recommendations for directions of the suture lines to minimise the suture force.
- Please list the main weaknesses of the paper. Please provide details, for instance, if you think a method is not novel, explain why and provide a reference to prior work.
The study contains no justification/explanation for the selection of an open-source Bartels library as the Finite Element “solver”/code of choice. Although reference to the Bartels library is provided, no summary of the finite element procedures used in this library (e.g. geometrically linear of non-linear analysis, static analysis, explicit dynamic analysis, implicit dynamics analysis etc.) is included.
No information is provided about the converge criteria used when computing the suture forces.
No justification is provided for selecting the UWG simulator as a reference method to ”validate” the results obtained in the study. Verification (rather than validation) may be a more appropriate term to describe evaluation of the results obtained using a given simulation/modelling method against other established simulation/modelling methods (Babuska and Oden 2004).
Comparison with the established simulation/modelling methods is the sole evaluation of the study results. Although it would be unrealistic (or even unreasonable) to expect validation against the experimental results or observations of the actual wound closing procedures at this stage of the study, lack of even short discussion of possible directions for such validation is the study weakness.
REFERENCES Babuska, I. and J. T. Oden (2004). “Verification and validation in computational engineering and science: basic concepts.” Computer Methods in Applied Mechanics and Engineering 193(36–38): 4057-4066.
- Please rate the clarity and organization of this paper
Excellent
- Please comment on the reproducibility of the paper. Note, that authors have filled out a reproducibility checklist upon submission. Please be aware that authors are not required to meet all criteria on the checklist - for instance, providing code and data is a plus, but not a requirement for acceptance
The Authors’ statements about the reproducibility of the paper appear to be correct/true. Including the input files for conducting the simulations may be one possible area for improvement.
- Please provide detailed and constructive comments for the authors. Please also refer to our Reviewer’s guide on what makes a good review: https://conferences.miccai.org/2023/en/REVIEWER-GUIDELINES.html
Providing a short justification for selection of the Finite Element library used in the study and reference method (UWG simulation) for evaluation of the results obtained in the study would make description of the methods used more complete.
Including a short statement about possible directions for validation of the results obtained/recommendations formulated against the experimental results and/or clinical would increase trust in the proposed modelling and simulation approach.
- Rate the paper on a scale of 1-8, 8 being the strongest (8-5: accept; 4-1: reject). Spreading the score helps create a distribution for decision-making
6
- Please justify your recommendation. What were the major factors that led you to your overall score for this paper?
The study appears to be relevant to surgical intervention. From the computational biomechanics perspective, the methods seem appropriate and the results obtained using the approach proposed in the study are quantitatively compared against other established modelling and simulation methods. The manuscript is very well organised and clearly written. It seems that relatively minor manuscript revision would be sufficient to address the study (and manuscript) weaknesses highlighted in this review.
- Reviewer confidence
Confident but not absolutely certain
- [Post rebuttal] After reading the author’s rebuttal, state your overall opinion of the paper if it has been changed
N/A
- [Post rebuttal] Please justify your decision
N/A
Review #2
- Please describe the contribution of the paper
This study evaluated suture forces to close a wound using FEM to find the most optimal flap orientation. The proposed method objectively and quantitatively evaluated the suture forces, which can improve the outcome of Rhomboid flap over the textbook knowledge.
- Please list the main strengths of the paper; you should write about a novel formulation, an original way to use data, demonstration of clinical feasibility, a novel application, a particularly strong evaluation, or anything else that is a strong aspect of this work. Please provide details, for instance, if a method is novel, explain what aspect is novel and why this is interesting.
Objective methodology to simulate and evaluate the required suture forces to close a wound using FEM. Anisotropic material with various properties were applied to validate the evaluation. Different scenarios of suturing (multi and single suture) were evaluated and compared.
- Please list the main weaknesses of the paper. Please provide details, for instance, if you think a method is not novel, explain why and provide a reference to prior work.
Skin surface was modelled as a membrane with planar stress only while the actual skin patch is three dimensional structures. This simplification can be a source of error. Likewise, non-linear Relaxed Skin Tension Lines (RSTL), which exist on the 3D skin surface was assumed to be a linear line on 2D plane, while the angle of the suturing is the most important factor in this study, which can also be a source of error.
- Please rate the clarity and organization of this paper
Excellent
- Please comment on the reproducibility of the paper. Note, that authors have filled out a reproducibility checklist upon submission. Please be aware that authors are not required to meet all criteria on the checklist - for instance, providing code and data is a plus, but not a requirement for acceptance
The reproducibility can be rated as sufficient.
- Please provide detailed and constructive comments for the authors. Please also refer to our Reviewer’s guide on what makes a good review: https://conferences.miccai.org/2023/en/REVIEWER-GUIDELINES.html
Please discuss the limitations of the current study. Please discuss if the simplification of the skin and RSTL is valid, ignoring three-dimensional nature of the skin structures. If not, please clarify it as the limitation of the study. The effect of skin properties was tested for each parameter at a time with others were fixed at the average value. Please discuss if the ranges of the current results (graphs with different colors in Fig. 5) are considered to include all the possible combinations (2 x 2 x 2 combinations) of property changes or if testing of all possible combinations is not necessary. In discussion, the authors explained the possible reason for the discrepancy between the findings of this study and textbook knowledge is that “the textbook knowledge might have tried to optimize a different goal or has taken other factors into account”. Please share more specific and detailed insight into the reason for the discrepancy. Is it because of simplification in the modeling in this study?
- Rate the paper on a scale of 1-8, 8 being the strongest (8-5: accept; 4-1: reject). Spreading the score helps create a distribution for decision-making
5
- Please justify your recommendation. What were the major factors that led you to your overall score for this paper?
Clinically valuable study but with limited technical innovation.
- Reviewer confidence
Very confident
- [Post rebuttal] After reading the author’s rebuttal, state your overall opinion of the paper if it has been changed
6
- [Post rebuttal] Please justify your decision
I agree with the authors’ response to the reviewers comments. But I would like to suggest the authors to revise the manuscript accordingly, clearly stating limitations and especially limiting the scope (or aim) of the study following the authors’ response: “We aim to compare the prediction made by this setup with textbook knowledge based on RSTLs. We want to bring to the reviewers’ attention that current textbook descriptions do not take the more complex facial differences into account.”
Review #3
- Please describe the contribution of the paper
This paper demonstrate a skin flap simulation using FEM, and calculated the optimal flap orientation as a recommendation.
- Please list the main strengths of the paper; you should write about a novel formulation, an original way to use data, demonstration of clinical feasibility, a novel application, a particularly strong evaluation, or anything else that is a strong aspect of this work. Please provide details, for instance, if a method is novel, explain what aspect is novel and why this is interesting.
- Skin flap simulation is demonstrated well in a supplemental movie.
- The proposed method provide a recommendation of a optimal skin flap orientation.
- Please list the main weaknesses of the paper. Please provide details, for instance, if you think a method is not novel, explain why and provide a reference to prior work.
- 2D simulation didn’t consider thickness of the skin and constraints of the muscles under the skin, although those factors can influence the deformation and forces in the skin flap.
- The proposed method was validated only within the simulation, and not validated with actual patients. So, the effectiveness is not clear.
- Please rate the clarity and organization of this paper
Good
- Please comment on the reproducibility of the paper. Note, that authors have filled out a reproducibility checklist upon submission. Please be aware that authors are not required to meet all criteria on the checklist - for instance, providing code and data is a plus, but not a requirement for acceptance
The given conditions in FEM during a skin flap procedure is quite unknown. So, it is difficult to reproduce the simulation and experiments. For example, the followings information are unknown or insufficient:
- The applied forces or given displacements during a skin flap procedure (In the supplemental movie, the flapped skin moves step by step, and the movement looks depending not on the simple applied forces. The applied forces look changing during skin flap. But, it is unclear how the temporal difference of applied conditions are determined. )
- How to match the nodes of different segments in a skin flap
- Please provide detailed and constructive comments for the authors. Please also refer to our Reviewer’s guide on what makes a good review: https://conferences.miccai.org/2023/en/REVIEWER-GUIDELINES.html
The FEM simulation of skin flap is interesting because the design of the skin deformation can be useful for the treatment. The reviewer found the work is promising. If this study can show the effectiveness with the actual patient data, then the reviewer totally agree with the effectiveness of the method. The facial skin deformation is governed by many different aspects including soft-tissue, muscles and bones. Even if the model is simplified, the effectiveness of the model is confirmed with the actual patient data. It would be valuable. Therefore, the reviewer recommend the authors check the effectiveness with the actual patient data because the authors simplify the mechanism of the facial skin deformation largely.
- Rate the paper on a scale of 1-8, 8 being the strongest (8-5: accept; 4-1: reject). Spreading the score helps create a distribution for decision-making
3
- Please justify your recommendation. What were the major factors that led you to your overall score for this paper?
This paper demonstrate a skin flap simulation using FEM, and calculated the optimal flap orientation as a recommendation. FEM-based deformable model has been studied for 30 years or more, and then the technology itself does not sound. However, its application to skin flap and the surgical planning is still under research.
Major concerns:
- The idea of skin flap FEM simulation and recommendation is interesting, however, if the authors conclude their findings, the validation using an actual skin flap results, not simulation is required. Otherwise, it is difficult to conclude the findings in this paper is meaningful in the real world.
- p.4 The authors described that “we set the radius of the patch to be 1 unit and the radius of the lesion to be 0.1 unit”. However, its validity of its boundary condition is not clear.
- The facial skin deformation is governed by many different aspects including soft-tissue, muscles and bones. How do the authors justify the validity of the proposed?
- Reviewer confidence
Very confident
- [Post rebuttal] After reading the author’s rebuttal, state your overall opinion of the paper if it has been changed
5
- [Post rebuttal] Please justify your decision
I found the other reviewers also had the similar concerns. Based on the authors’ feedback, if the authors describe the limitations or the justification of the authors’ choices of the simple skin model and evaluation without patients. I would agree for acceptance weakly.
Primary Meta-Review
- Please provide your assessment of this work, taking into account all reviews. Summarize the key strengths and weaknesses of the paper and justify your recommendation. In case you deviate from the reviewers’ recommendations, explain in detail the reasons why. In case of an invitation for rebuttal, clarify which points are important to address in the rebuttal.
The paper, which relies on an FEM-based approach, has received mixed votes and therefore options for further discussions should be granted to the authors. The authors should address points raised by the reviewers with regard to evaluation and comparison to other works. Furthermore, R3 raised several conserns about oversimplification made by the approach,e.g. facial skin deformation is governed by many different aspects including soft-tissue, muscles and bones. The authors are invited to comment on these points.
Author Feedback
Thanks to all reviewers (R1, R2, R3, Meta-R) for taking the time to review and provide feedback for our submission. Please see below for our response to major weaknesses:
- Over-simplification of the setup (R2, R3, Meta-R): We agree that the complex physical structure of the human face would introduce additional constraints to the suture force. a) Baseline study: In this study, we set up the baseline case with a 2D planar patch. We aim to compare the prediction made by this setup with textbook knowledge based on RSTLs. We want to bring to the reviewers’ attention that current textbook descriptions do not take the more complex facial differences into account. Yet, the generic textbook knowledge and RSTLs are used as guidelines for orientating skin flaps in a clinical setting. However, the resulting flap rotations for different material properties are consistent and they are overall close to the textbook descriptions which is a suitable validation for our methods. Of course, we could add in other facial parameters and then compare this to our baseline model. b) Existing Literature: The 2D planar setup has been used in skin flap simulation in many other SOTA literature (not used to determine the optimal rotation yet, see Refs. 9-24). Using a single direction to represent RSTLs is also the most common approach in the existing literature. Thus, this simplified model should be an acceptable assumption (with some limitations discussed below).
- Validation against patient data (R2, R3, Meta-R): As far as we know, no database exists on the most optimal skin flap orientation based on patient data. There are two potential ways to obtain this data: a) Collecting data from clinical procedures: This could involve having a physical setup to measure suture forces and tracking the healing process of each patient. To validate the hypothesis in our study, we will need surgeons to orient the flap according to our recommendations and have a control group of patients that undergo similar surgeries with the original textbook knowledge. The drawback is that each patient might need their surgery in a different location. In an animal study, this issue could be mitigated. Nevertheless, it will involve significant effort, costs, and a longer project to collect enough cases. Ethics approval is required before we can proceed with such experiments. Our current study can serve as preliminary data to establish the hypothesis of the changes in optimal flap orientation. b) Building a database based on surgeons’ opinions: The patient specific skin flap designs made by surgeons could involve many subjective factors. Thus, there could be discrepancies among surgeons for each patient case. Therefore, one aim of our work is to establish an objective way to determine the orientation of skin flaps relative to RSTLs. Due to the above reasons, it is very difficult to build a database based on patient data and our current best approach is to compare with established and widely-accepted textbook knowledge. However, as future work, we will consider one or more approaches mentioned above for validation.
- FEM setup (R1, R2, R3): To reproduce this work, we don’t rely on a specific setup of one FEM library. We implemented the FEM simulation in Bartels, but one could use any FEM library/program. Additionally, to reduce the effect of patch boundary, we used a patch with a relatively large size. The size ratio of the patch and lesion does not have any significance as long as the patch is large enough. We are happy to share more details of the FEM setup (e.g. convergence criteria, FEM model, single suture force values) to improve the reproducibility of the experiments.
- Lack of discussion of the limitations (R1, R2): Due to the simplification of the model, one limitation might be that its preferred usage is on relatively flat regions of the face. Additionally, we have not considered the effect of nearby facial features, which is a common scenario on a patient’s face.
Post-rebuttal Meta-Reviews
Meta-review # 1 (Primary)
- Please provide your assessment of the paper taking all information into account, including rebuttal. Highlight the key strengths and weaknesses of the paper, clarify how you reconciled contrasting review comments and scores, indicate if concerns were successfully addressed in the rebuttal, and provide a clear justification of your decision. If you disagree with some of the (meta)reviewer statements, you can indicate so in your meta-review. Please make sure that the authors, program chairs, and the public can understand the reason for your decision.
The reviewers have reached consensus after rebuttal and felt that most of their issues have been addressed in the rebuttal. The authors should revise their paper as stated for camera-ready version.
Meta-review #2
- Please provide your assessment of the paper taking all information into account, including rebuttal. Highlight the key strengths and weaknesses of the paper, clarify how you reconciled contrasting review comments and scores, indicate if concerns were successfully addressed in the rebuttal, and provide a clear justification of your decision. If you disagree with some of the (meta)reviewer statements, you can indicate so in your meta-review. Please make sure that the authors, program chairs, and the public can understand the reason for your decision.
I would lean towards accepting this paper. The authors have addressed the original concerns of the reviewer and are now all in favour of acceptance (accept, accept, weak accept). The study which evaluated suture forces to close a wound using FEM to find the most optimal flap orientation can have real surgical implications and could be interesting to the community.
Meta-review #3
- Please provide your assessment of the paper taking all information into account, including rebuttal. Highlight the key strengths and weaknesses of the paper, clarify how you reconciled contrasting review comments and scores, indicate if concerns were successfully addressed in the rebuttal, and provide a clear justification of your decision. If you disagree with some of the (meta)reviewer statements, you can indicate so in your meta-review. Please make sure that the authors, program chairs, and the public can understand the reason for your decision.
After the rebuttal stage all of the reviewers agree this is a manuscript worthy of publication in MICCAI 20233.