Dear Dr. Buffet-García,

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PLOS ONE

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Additional Editor Comments (if provided):

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Partly

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2. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Thank you for the opportunity to review this study. The present manuscript investigates the intra- and inter-rater reliability of shear wave elastography (SWE) measurements of the psoas major (PM) muscle. The study is well designed and clearly written, and the results suggest that SWE may be a reliable method for assessing PM stiffness in patients with low back pain (LBP). I appreciate the authors’ contribution to this area of musculoskeletal research. Nevertheless, I have several comments that I believe would strengthen the manuscript, particularly regarding the methodology.

Introduction:

-The Introduction is somewhat lengthy. The detailed description of the PM functional anatomy may be reduced or moved to the Discussion if necessary.

Methods:

-Was participants’ physical activity level controlled prior to the SWE assessment? For example, performing physical exercise or manual labor immediately before measurement could influence the mechanical properties of the PM. This potential confounder should be discussed

-Given that the PM is located relatively deep, was the depth of the region of interest (ROI) recorded during SWE acquisition? Depth can influence modulus values. If the depth varied across measurements or between participants, this should be considered in the interpretation.

-In each SWE measurement session, was only one SWE image acquired? If so, this should be stated clearly. Since SWE values tend to be quite sensitive to how transducer is manipulated, acquiring and averaging multiple scans would reduce measurement error and improve reliability. Please clarify.

-The classification thresholds for intraclass correlation coefficient (ICC) (e.g., moderate, good, excellent) should be explicitly defined, preferably with references.

-It would enhance the clinical impact of the study if SWE values were compared to physical examination findings associated with PM stiffness, such as the Thomas test or hip extension range of motion.　Furthermore, including healthy volunteers as a comparison group would have helped interpret whether elevated stiffness values are indeed associated with LBP.

Results:

-There seems to be a discrepancy in participant numbers. Table 1 reports 16 men and 31 women, which sums to 47, yet the total number of participants is stated as 52. Please confirm and correct this inconsistency.

Discussion

-Lines 338–344: The average BMI of both male and female participants exceeds 25, indicating that some may be classified as overweight or obese. Obesity can lead to intramuscular fatty infiltration, including in the PM. Could the relatively higher Young’s modulus observed in this study be attributed, at least in part, to fatty infiltration rather than LBP per se?

-Please add the limitations of this study.

Table

-As mentioned in the main text, please include p-values to support the statistical significance of the comparisons.

Reviewer #2: Thank you for the opportunity to review this manuscript aimed to evaluate the intra and inter-examiner reliability of shear wave elastography for calculating the PM stiffness in patients with LBP. While the approach is rigor and the findings are important, I would like to point out some methodological and interpretation concerns.

Major comments

1. While psoas major CSA changes and fatty infiltration were clearly described in L98-112, these changes did not necessarily align with the main aim, which was to evaluate the reliability of stiffness measurements. The introduction should reduce or eliminate these descriptions to focus on the need for a validated method to quantify muscle stiffness in LBP patients.

2. To further strengthen the rationale for this study, the authors should mention the prior reliability study in healthy subjects by Zhou et al. in the introduction. Following this, the authors should hypothesize why these findings of high reliability may not be generalizable to patients with LBP.

3. L181. The study analyzes muscles from both sides of the body. It is possible that data from the left and right sides of the same participant are not independent. I wonder if this lack of independence can cause the intraclass correlation coefficient (ICC) to increase. The potential influence of this non-independence on the statistical results should be discussed or addressed within the statistical model.

4. L254. While the authors assessed consistency within and between examiners using ICC(3,1) and ICC(3,2), they may overlook systematic error, which would be an issue in clinical settings. To provide a more comprehensive evaluation of reliability, I suggest adding an ICC(2,1), which incorporates both random and systematic error. Also, please calculate the SEM and MDC using the ICC(2,1) value.

Specific comments

Abstract

5. L66. The conclusion states, "Excellent test-retest reliability was observed for the measurement of PM muscle stiffness... by both experienced and novice evaluators." However, this statement should be revised to acknowledge the statistically significant difference between the two trials for the novice examiner.

Introduction

6. L95�”including” is a typo.

Methods

7. L191. What is the rationale behind including 52 participants, despite having confirmed that the minimum sample size was 29? Could using a larger sample size lead to an overestimation of reliability?

8. L232. Please add the region of interest size.

9. The manuscript does not explain how Young's modulus was calculated from the shear wave speed. To ensure reproducibility, the authors must provide the formula used and any assumptions made (e.g., tissue density).

10. Please add the information on imaging processing, such as smoothing an so on.

11. The authors have two values of each muscle in each examiner. Which data (trial 1 or 2?) do the author use to calculate ICC(3,1)?

Results

12. L264: The statement "Every image acquired during data collection was deemed valid" is concerning. Were there pre-defined criteria for image acceptability? The absence of any excluded images in 416 acquisitions seems unlikely and requires explanation.

13. L265. The manuscript has stated that the total number of participants is 52. However, 31 females and 16 males add up to 47. Please correct.

14. L267. Did you acquire two consecutive images without removing the probe, or did you reposition the probe before the second measurement?

15. L272. This section includes data for "Water volume" and “body composition”, but the method to measure these variables is not described in the Methods section.

16. Please consider adding the coefficient of variation alongside ICC to provide a more complete assessment of measurement variability, especially given the differing scales of shear wave velocity and Young’s modulus.

17. Bland-Altman plots are presented in the results, but this analysis is not described in the Methods section. Furthermore, the authors should analyze the presence or absence of systematic and proportional error using the plots and statistical tests.

Discussion

18. L338. In the Discussion, the authors compared their Young's modulus values with data from the study by Zhou et al. However, the two studies used different ultrasound systems (Canon vs. Aixplorer). Without established inter-machine reliability, particularly for deep muscles, this direct comparison is not valid. Therefore, I believe this comparison should be avoided.

19. The authors should acknowledge that evaluating only one portion of the PM at rest is a limitation that restricts the generalizability of the study.

Figure/Caption

20. Figure 1: The figure, particularly the left-hand schematic, appears very similar to a figure in the publication with PMID: 40150065. If this figure has been adapted or inspired by another source, that source must be appropriately cited. Also, in Figure1’s caption, “mayor” is a typo.

21. Figure 2: The caption for the Bland-Altman plots should explain what the solid red lines and the dashed lines represent. Additionally, the dashed lines appear curved in the figure; please confirm if this is an error or an intended feature of the plotting method.

22. Table2. In trial 2, the novice examiner measured a mean shear wave speed of 2.09 m/s and a Young’s modulus of 16.03 kPa, while the experienced examiner measured a higher shear wave speed of 2.15 m/s but a lower Young’s modulus of 15.9 kPa. Is this discrepancy due to different calculation methods, or is it a reporting error?

23. Table 3. I was not sure how the mean, error, and absolute error were calculated.

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what does this mean? ). If published, this will include your full peer review and any attached files.

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Reviewer #1: No

Reviewer #2: No

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Shear Wave Elastography for measuring the elastic properties of the Psoas Major muscle: an intra- and inter-examiner reliability study

PONE-D-25-25182R1

Dear Dr. Buffet-García,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Masatoshi Nakamura, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions??>

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #1: Yes

Reviewer #2: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: The author has sufficiently addressed all of my comments. The revised manuscript has been improved accordingly and is now suitable for publication.

Reviewer #2: Thank you for addressing all my comments. I feel you have responded carefully to the concerns I raised. I have just one point, which may be a difference in perspective: while I agree with the interpretation of ICC(3,1) and ICC(2,1), I believe that since the SEM and MDC are also derived from ICC(3,1), they fail to account for the influence of systematic error.

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what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy

Reviewer #1: No

Reviewer #2: No

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