Impact of Gait-Synchronized Vibrotactile Sensory Feedback on Gait in Lower Limb Amputees

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this study, the authors conducted systematic evaluations of gait performance in amputee subjects, users of lower limb prostheses, following the implementation of a vibrotactile feedback system synchronized with gait. The topic is highly relevant in the field of bioengineering and biomechanics of prosthetic systems, areas that have been extensively researched. In this context, the study is interesting and pertinent. However, the authors have addressed the background of the topic briefly, so it would be advisable to further expand on this in the introduction section. To date, several sensory feedback systems have been implemented, including those based on vibrotactile, electrical stimulation, and proportionally directed pressures, among others. This raises a question that should be addressed throughout the study: does vibrotactile stimulation offer any advantage over other sensory modalities, or was it simply selected to evaluate the commercial system from Saphenus (https://saphenus-med.com/)?

In light of the results obtained, the discussion is adequately presented; however, I believe the authors could improve the analysis by providing a deeper and more detailed approach.

Standardized gait tests were performed on the subjects before and after the trial period. In their descriptions, the authors mention that, before the trial period, subjects were evaluated without the system, while at the end, they were evaluated with the system activated. Are these two situations truly comparable? Wouldn’t it be more appropriate to compare the evaluations at the start of the trial period with the system turned on? I understand that, at the initial stage, the subjects had no prior experience with the vibrotactile system, but the before and after conditions seem more equivalent. How do the authors justify the comparison chosen for this study?

Lines 131-132: What do they mean by amputation type, standard or innovative?

Line 118: In the 'Functional Gait Assessment' subsection, the authors should briefly describe the methods used to capture and determine gait parameters, such as the Timed 'Up and Go' Test (TUG), Four Square Step Test (FSST), 10 Meter Walk Test (10MWT), and 2 Minute Walk Test (2MWT), as well as the procedures and formulas employed to calculate the evaluation metrics. Additionally, were these parameters determined using the same plantar pressure sensing system?

How are the performances in Figs. 6, 7, 8, and 9 related to the system usage times? The statistical analysis model used should take into account the time users spent using the system.

How could the parameters mentioned in subsection 2.6 (line 128) influence the results obtained?

Minor

The abstract needs to be rewritten. While the sentences are understandable, they need adjustments to improve readability.

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents the clinical evaluation of the effect of a vibrotactile haptic feedback system for lower limb prosthesis users following long term use (30-120 days). The haptic feedback is derived from a force instrumented insole and provides haptic feedback to the thigh. Even without statistically significant results, the results show an interesting trend towards improvement of clinical mobility metrics which encourages further exploration of this intervention. While the extreme heterogeneity of the cohort (different amputation levels, wearing the sleeve on different thighs, significant co-morbidities impacting performance) and the lack of intra-participant repeated measures or higher resolution longitudinal data limit how much can be extrapolated from this data set, it provides an interesting baseline for future work which, has not yet been well established and as such is an impactful contribution to the field. I suggest the following edits to the authors which I hope may further improve the manuscript. I have separated the comments into major and minor.

 

Major

 

1.     1. The total time each participant used the system should be reported in the results. This is a crucial piece of information which could reveal some insight into the potential temporal trends in adaptation across the cohort. While the number of days each participant used the device would be interesting alone, if you also have step count data or some metric describing how much the device was actually used during this time, it could be even more relevant. I would also be curious if there is a trend in your outcome metrics which correlates to total time using the haptic feedback system. While it is intuitive to think that more time using the device will result in more benefit, it would be an equally interesting result if there is no correlation to time used. I believe including the usage time data and analysis would significantly increase the impact of the manuscript.

 

2.     2. What was the tuning procedure used for sensor threshold, vibration magnitude, and vibration duration? A consistent tuning procedure is also an important piece of the methodology to ensure consistent results. Inadequate feedback intensity may result in poor information transfer, while excessive feedback intensity could result in annoyance or desensitization of the skin to the vibration.

 

3.     3. Since Subject 10 was unable to perform the 10MWT and the 2MWT during the baseline data collection due to post operative pain, their follow up data for those tests should be excluded from the cohort analysis. The improvements due to haptic feedback cannot be isolated from the improvement due to reduced pain from healing.

 

4.     4. In the discussion, the authors mention that the time since amputation may play a role in the limited significance of the outcomes. This is a fair hypothesis. Was any data analysis performed to see if there was a trend in improved performance metrics and recency of amputation? This could be an interesting result to support the hypothesis.

 

5.     5. The cohort in this study is extremely heterogenous especially given the description of substantial co-morbidities in the discussion which could impede user performance. While I understand that your analysis is already limited by sample size, have you investigated if there are any trends in sub-group responses? Such as those without co-morbidities which may cap performance (i.e., excluding 2, 4, and 10), those with the same amputation level and unilateral/bilateral prosthesis use, or those that could wear the band on the ipsilateral side? While the statistical strength will not be present, it may be interesting to see if a certain subgroup has a more notable trend in any of your metrics, especially given the extreme heterogenous nature of the prosthesis user population potentially meriting more individualized analysis of the impact of assistive technologies such as described in “Subject-specific responses to an adaptive ankle prosthesis during incline walking” by Lamers et al. Further, identification of a group who stands to benefit most could inspire a more focused direction of future work.

 

Lamers, E. P., Eveld, M. E., & Zelik, K. E. (2019). Subject-specific responses to an adaptive ankle prosthesis during incline walking. Journal of biomechanics, 95, 109273.

 

Minor

 

1.     1. Could the participants’ K levels be reported in Table 2?

 

2.     2. In the discussion it is stated that the improvement in the 10MWT but lack of improvement in the 2MWT suggests that while walking speed was potentially improved by haptic feedback, walking endurance was not. Do the authors have any insight on the clinical significance of an improvement to walking speed if it is not significant enough in duration to be discerned in the 2MWT?

 

3.     3. On page 3, the scale for vibration strength “(0-100%)” is placed next to the word “adjusted” rather than the word “strength” unlike the scale for vibration duration.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have improved the introduction section by emphasizing that, although there are numerous studies on vibrotactile feedback systems, most have focused on enhancing users' balance and posture rather than addressing dynamic analyses, as proposed in this work. This clarification is particularly relevant for contextualizing the hypothesis and objectives of the research.

Regarding the response about the scenarios compared in the study, I find it reasonable. Indeed, the use of the vibrotactile stimulation system at the beginning of therapy could influence the results, as the lack of familiarity with this type of stimulation might affect gait. I appreciate this clarification.

My main concerns have been satisfactorily addressed by the authors. The work has been significantly improved and represents an important contribution to the study of biomechanics in lower limb prosthesis users.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The revisions to the manuscript have resolved my concerns. I look forward to seeing the published article.

Author Response

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