Robot-Assisted Ankle Rehabilitation Using the Hybrid Assistive Limb for Children after Equinus Surgery: A Report of Two Cases

Round 1

Reviewer 1 Report

Thank you for the opportunity to review this manuscript titled: Robot-Assisted Ankle Rehabilitation Using Hybrid Assistive 2 Limb® in Children Following Equinus Surgery: A Report of Two Cases. This is a case report that could represent an advance in the treatment of motor consequences in children with spasticity in the lower limbs. The introduction is correct. The justification of the problem and relevance of the intervention are well described. The methodology is explained in detail, as well as the result variables. The results are exposed rigorously. Here are some aspects that should be clarified:

 

ABSTRACT:

1.    P1Ln20. It would be interesting to briefly review the main advantage of this device compared to conventional techniques.

 

INTRODUCTION

2.    P1Ln36. In children in general or with any pathology?

3.    P2Ln52-54. Include reference.

4. Could the novelty of this case be indicated with respect to others? Indicate if it is a pioneer treatment in children with neurological pathologies, point out previous experiences in which this device was used in other pathologies (for example, Matsuda 2022 in patients with foot drop), etc.

 

CASE PRESENTATION

4.    P3Ln78. Did the subjects or legal guardians complete an informed consent for the study?

5.    P3Ln78. Specify if both subjects had more motor problems in the lower limbs.

6.    P4Ln111-113. Could more details be provided about these rehabilitation treatments, physical therapy and occupational therapy?

7.    Figure 4. Training was “performed/done” 20 minutes per session; better "sessions" instead of "times" to correlate with the previous phrase; include “2-4 sessions per week”.

8.    P5Ln122. Immediately after?

9.    P5Ln126. Please include references for each study variable. The two paragraphs (Ln127-134) could be unified. For joint measurement, indicate which measurement instrument was used, in which global position the subject was placed, and whether the procedure was the same as when initial data was provided on page 3.

10. P6Ln155. What outcome variables are obtained from this assessment procedure? ROM, speed, …

 

DISCUSSION

11.  P11Ln286. Please explain the meaning of FES, used for the first time here. Why is this term not used in the introduction?

12.  What are the differences in the results using this device compared to conventional treatments? Is it worth the economic investment that this device requires to improve the results?

Author Response

Response to Comments.

Thank you for your comments. We have made changes to improve the manuscript in accordance with your suggestions. The revised parts of the text are shown in red.

ABSTRACT:

Comment 1.    

P1Ln20. It would be interesting to briefly review the main advantage of this device compared to conventional techniques.

Response 1.

Thank you for this suggestion. We have provided this information on page 1, lines 20-23.

Previous MS. P.1, Lines 20-22

The single-joint Hybrid Assistive Limb (HAL-SJ) has a bioelectrical signal-based control system and demonstrates joint torque assistance with the wearer’s voluntary drive.

Revised MS. P.1, Lines 20-23

The single-joint Hybrid Assistive Limb (HAL-SJ) is an advanced exoskeletal robotic device with a control system that uses bioelectrical signals to assist joint motion in real time and demonstrates joint torque assistance with the wearer’s voluntary movement.

INTRODUCTION

Comment 2.   

P1Ln36. In children in general or with any pathology?

Response 2.

Thank you for this important question. The targeted pathology is a gait disorder caused by central nervous system disorders of pediatric patients. We have revised the text to reflect this comment.

Previous MS. P.1, Line 36

Equinus is the most common cause of gait disorders in children, ...

Revised MS. P.1, Lines 36-37

Equinus is the most common gait disorder caused by central nervous system (CNS) disorders of pediatric patients; …

Comment 3. 

P2Ln52-54. Include references.

Response 3.

Thank you for this suggestion. We have added a reference.

Revised MS. P.2, Line 54

Therefore, after surgery, the use of the range of motion (ROM) gained in the ankle joint is important to performing repeated dorsiflexion/plantar flexion and standing balance exercises [9].

Comment 4.

Could the novelty of this case be indicated with respect to others? Indicate if it is a pioneer treatment in children with neurological pathologies, point out previous experiences in which this device was used in other pathologies (for example, Matsuda 2022 in patients with foot drop), etc.

Response 4.

Thank you for this suggestion. We have added text in reference to this comment.

Revised MS. Lines P.2, Lines 73-75

Ankle rehabilitation using the HAL-SJ has been attempted for adult patients with drop foot, and improvements in muscle activity, strength, and walking speed have been reported [15, 16].

CASE PRESENTATION

Comment 5.

 P3Ln78. Did the subjects or legal guardians complete an informed consent for the study?

Response 5.

Thank you for this suggestion. We have added the ethical considerations.

Revised MS. P.8, Lines 220-227

2.5. Ethical considerations

This study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Ibaraki Prefectural University of Health Sciences (approval number: 797; date of approval: December 28, 2017; approval update: approval number: e356; date of approval: June 8, 2022). Informed consent was obtained in writing from the parents or guardians of the patients involved in the study because they were minors. The research participants were also present during the explanation of the study to confirm their willingness to participate in the study.

Comment 6.

P3Ln78. Specify if both subjects had more motor problems in the lower limbs.

Response 6.

Thank you for this suggestion. We have described the left and right differences in spasticity in case 1. Case 2 is a child with left-side hemiplegia.

Previous MS. P.3, Line 82

He underwent surgery because of worsening of his right equinus (Figure 2b).

Revised MS. P.3, Lines 99-100

He had more severe spasticity on the right side than on the left side, and his right equinus worsened; therefore, he underwent surgery (Figure 2b).

Comment 7.

P4Ln111-113. Could more details be provided about these rehabilitation treatments, physical therapy and occupational therapy?

Response 7.

Thank you for this suggestion. We have added details of the physical therapy and occupational therapy.

Previous MS. P.4, Line 110-113

We performed HAL-SJ training in addition to conventional rehabilitation during hospitalization, and physical therapy and occupational therapy were performed five times a week for 40–60 min per session.

Revised MS. P.5, Lines 129-134

We performed HAL-SJ training in addition to conventional rehabilitation during hospitalization. Physical therapy and occupational therapy were performed for 40–60 min per session; five sessions were performed each week. Physical therapy included stretching, muscle strengthening exercises, physical fitness exercises, and walking practice. Occupational therapy included training to perform activities of daily living.

Comment 8.

Figure 4. Training was “performed/done” 20 minutes per session; better "sessions" instead of "times" to correlate with the previous phrase; include “2-4 sessions per week”.

Response 8.

Thank you for this suggestion. We have corrected this in Figure 4. Additionally, we have corrected the text.

Previous MS. Figure 4

8 times in total

Revised MS. Figure 4

Total of 8 sessions

Previous MS. P.4, Line 110-113

We performed HAL-SJ training in addition to conventional rehabilitation during hospitalization, and physical therapy and occupational therapy were performed five times a week for 40–60 min per session.

Revised MS. P.5, Lines 129-131

We performed HAL-SJ training in addition to conventional rehabilitation during hospitalization. Physical therapy and occupational therapy were performed for 40–60 min per session; five sessions were performed each week.

Comment 9.

P5Ln122. Immediately after?

Response 9.

Thank you for this important question. Within half a day to 2 days after completion of HAL-SJ training, the end-of-training assessments were performed.

Revised MS. P.6, Lines 142-143

Assessments were performed before and after HAL-SJ training. End-of-training assessments were conducted within half a day to 2 days after the completion of HAL-SJ training.

Comment 10.

P5Ln126. Please include references for each study variable. The two paragraphs (Ln127-134) could be unified. For joint measurement, indicate which measurement instrument was used, in which global position the subject was placed, and whether the procedure was the same as when initial data was provided on page 3.

Response 10.

Thank you for this suggestion. We have made the necessary changes.

Previous MS. P.5, Line 127-132

We performed the 10-m-walking test, ROM, Modified Ashworth Scale (MAS), Selective Control Assessment of the Lower Extremity (SCALE), and Gross Motor Function Measure (GMFM).

The 10-m walking test assessed the walking speed, length, and cadence. The 10-m walking test was performed at a selected walking speed. ROM was measured using dorsiflexion and knee joint extension (DKE).

Revised MS. P.6, Lines 148-155

We evaluated the 10-m walking test results, ROM, Modified Ashworth Scale (MAS) score, Selective Control Assessment of the Lower Extremity (SCALE) score, and Gross Motor Function Measure (GMFM) [17-21]. The 10-m walking test assessed the walking speed, length, and cadence and was performed at a selected walking speed. The ROM was measured using dorsiflexion and knee joint extension. The ROM was assessed in the supine position using goniometry, as recommended by the American Academy of Orthopaedic Surgeons [18]. The initial ROM before training was assessed by orthopedists; however, ROM before and after HAL-SJ training was assessed by a physical therapist.

Comment 11.

P6Ln155. What outcome variables are obtained from this assessment procedure? ROM, speed, …

Response 11.

Thank you for this important question. Gait analysis using three-dimensional gait analysis was used to measure joint angles during the gait cycle. However, gait speed, stride length, and walking speed were measured using the 10-m walking test (P.6, Lines 145-146). We have added gait analysis details.

Revised MS. P.7, Lines 165-166

A three-dimensional gait analysis was performed to determine the joint angles during the gait cycle.

DISCUSSION

Comment 12.

P11Ln286. Please explain the meaning of FES, used for the first time here. Why is this term not used in the introduction?

Response 12.

Thank you for this important question. We have added FES details.

Revised MS. P.2, Lines 54-58

Furthermore, functional electrical stimulation (FES) has been reported to be effective for improving gait function after pediatric orthopedic surgery [10]. FES provides electrical stimulation via skin surface or implantable electrodes to cause coordinated contraction of skeletal muscles to create goal-directed movement [10, 11].

Previous MS. P.11, Lines 286-289

Therefore, postoperative rehabilitation of pediatric equinus is important. FES has been the focus of attention in rehabilitation to improve gait function after pediatric orthopedic surgery.[16] Nonetheless, in our clinical treatment, we understood that many children who experienced FES were afraid of pain and were reluctant to undergo FES treatment.

Revised MS. P.12, Lines 298-302

FES can effectively improve dorsiflexion and plantar flexion [10, 11, 25]. However, FES may be invasive [10]. Furthermore, during our clinical experience, we have found that many children who underwent electrical stimulation, including FES, are hesitant to undergo electrical stimulation because of the fear of pain. However, HAL-SJ training is a non-invasive treatment.

Comment 13.

What are the differences in the results using this device compared to conventional treatments? Is it worth the economic investment that this device requires to improve the results?

Response 13.

Thank you for this important question. We have made the necessary changes.

Revised MS. P.12, Lines 298-309

FES can effectively improve dorsiflexion and plantar flexion [10, 11, 25]. However, FES may be invasive [10]. Furthermore, during our clinical experience, we have found that many children who underwent electrical stimulation, including FES, are hesitant to undergo electrical stimulation because of the fear of pain. However, HAL-SJ training is a non-invasive treatment. Children who have undergone HAL-SJ training can perform repeated ankle dorsiflexion and plantarflexion exercises, which are important for improving postoperative function, without the fear associated with pain. Additionally, HAL-SJ can assist with voluntary ankle dorsiflexion and plantar flexion movements in real time using BES feedback. Furthermore, patients experience neuromuscular motor training and coordination of muscle co-contraction, which may have a motor learning effect. Therefore, the HAL-SJ could be an effective rehabilitation device after equinus corrective surgery.

Revised MS. P.13, Lines 360-363

If HAL-SJ training facilitates functional recovery after equinus surgery, then it will shorten the rehabilitation period and reduce the economic burden experienced by the patient’s family. Additionally, if the risk of recurrence of equinus is reduced, then it would result in a significant economic benefit.

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

I really liked the article and think it could have a positive impact on something difficult to carry out and potentially life changing for children.  However, there are several places improvements should be made.

1. You never defined FES or how it is used in your introduction.  You allude to it but do not explicitly state it.  Please do.

 

2. In your introduction you focus on dorsiflexion and plantar flexion.  However, in your results you talk about this ankle angle as well as knee angles and hip angle.  I understand this is a linked system and the movement of one joints effects others, but some readers may not.  I suggest adding some explanation about this.

3. I also suggest linking directly equinus with a reduced dorsiflexion and calcaneus with reduced plantarflexion.  If you know these clinical signs it is obvious again but can quickly be defined to increase readability.

4. COI, I appreciate the walkthrough in the methods here. However, I suggest comparing the recovery to a normal average instead of theoretical absolutes.  This should add credibility to your intervention.

5. Reporting joint angles and % Gait cycle is reasonable but a reference to real life would help interpret.  For example when is swing and stance, is zero straight, or segments completely on top of each other.  What does a negative angle mean?

6. At times your word choice is not ideal and some sentences need another word to make clearer.  For example, "Furthermore, equinus recurrence may occur in the long term." I suggest changing to "Furthermore, equinus may return over time post-surgery." 

7. The first paragraph of the discussion which is potentially the most important has a number of sentences which I can guess what you mean.  As the authors I encourage you to make clearer what you want me to take away from your study.

 

 

Author Response

Response to Comments.

Thank you for your comments. We have made changes to improve the manuscript in accordance with your suggestions. The revised parts of the text are shown in red.

Comment 1.  

You never defined FES or how it is used in your introduction.  You allude to it but do not explicitly state it.  Please do.

Response 1.

Thank you for this suggestion. We have added details regarding FES.

Revised MS. P.2, Lines 54-58

Furthermore, functional electrical stimulation (FES) has been reported to be effective for improving gait function after pediatric orthopedic surgery [10]. FES provides electrical stimulation via skin surface or implantable electrodes to cause coordinated contraction of skeletal muscles to create goal-directed movement [10, 11].

Previous MS. P.11, Lines 286-289

Therefore, postoperative rehabilitation of pediatric equinus is important. FES has been the focus of attention in rehabilitation to improve gait function after pediatric orthopedic surgery.[16] Nonetheless, in our clinical treatment, we understood that many children who experienced FES were afraid of pain and were reluctant to undergo FES treatment.

Revised MS. P.12, Lines 298-302

FES can effectively improve dorsiflexion and plantar flexion [10, 11, 25]. However, FES may be invasive [10]. Furthermore, during our clinical experience, we have found that many children who underwent electrical stimulation, including FES, are hesitant to undergo electrical stimulation because of the fear of pain. However, HAL-SJ training is a non-invasive treatment.

Comment 2.

In your introduction you focus on dorsiflexion and plantar flexion.  However, in your results you talk about this ankle angle as well as knee angles and hip angle.  I understand this is a linked system and the movement of one joints effects others, but some readers may not.  I suggest adding some explanation about this.

Response 2.

Thank you for this suggestion. We have added a discussion of angular changes in the proximal joint effects.

Revised MS. P.13, Lines 326-330

The results of the three-dimensional gait analysis showed improved maximum hip extension and knee extension angles in the stance phase in case 1. During the equinus gait, the rocker bottom action at the heel is lost because of initial contact by the toe. This disruption of the normal sagittal plane ankle motion contributes to the compensatory deviations at the proximal joints [26].

Comment 3.

I also suggest linking directly equinus with a reduced dorsiflexion and calcaneus with reduced plantarflexion.  If you know these clinical signs it is obvious again but can quickly be defined to increase readability.

Response 3.

Thank you for this suggestion. We have added a description of equinus and calcaneus.

Previous MS. P.2, Lines 57-60

Bolton et al. have reported that after a mean follow-up of 6.9 years for calf lengthening surgery in children with cerebral palsy, 22% had a recurrence of equinus, and 36% had a recurrence of calcaneus.^[9] This finding illustrates the difficulty and importance of postoperative rehabilitation.

Revised MS. P.2, Lines 60-63

Bolton et al. reported that after a mean follow-up of 6.9 years performed for children with cerebral palsy (CP) who underwent calf lengthening surgery, 22% had recurrence of equinus (dorsiflexion was reduced) and 36% had recurrence of calcaneus (plantarflexion was reduced) [12].

Comment 4.

COI, I appreciate the walkthrough in the methods here. However, I suggest comparing the recovery to a normal average instead of theoretical absolutes.  This should add credibility to your intervention.

Response 4.

Thank you for this suggestion. We have added more information.

Revised MS. P.13, Lines 345-359

COI values can quantify co-activation using surface EMG values and range from 0 (no co-activation) to 1 (co-activation present) [24]. The COI values of the tibialis anterior and medial gastrocnemius in this study were compared to those obtained by other studies. Inoue et al. reported COI values during walking with and without a cane of 11 adult patients with CP [30]. The study by Inoue et al. differed from ours because it classified the gait cycle into two phases: the support phase and the swing phase. According to their study, the COI values of CP patients without a cane were 0.57 ± 0.09 in the stance phase and 0.46 ± 0.09 in the swing phase [30]. Our results showed that the COI values on the operative side before HAL-SJ training were higher than those observed during the previous study (operative side COI in the stance phase: case 1, 0.77 ± 0.19 and case 2, 0.68 ± 0.21; operative side COI in the swing phase: case 1, 0.57 ± 0.21 and case 2, 0.54 ± 0.12). After training, COI values decreased to below the standards of adult CP patients during the stance phase in case 1 and during the stance and swing phases in case 2. Excessive co-contraction of the antagonist and agonist muscles increases joint stiffness and inhibits smooth movement. Therefore, it is important to maintain moderate co-contraction [23].

Comment 5.

Reporting joint angles and % Gait cycle is reasonable but a reference to real life would help interpret.  For example when is swing and stance, is zero straight, or segments completely on top of each other. What does a negative angle mean?

Response 5.

Thank you for this suggestion. We have added a discussion of the 3D gait analysis

Revised MS. P.12-13, Lines 336-344

Additionally, the typical gait cycle is characterized by a 60% stance phase (of which 20% is the double stance) and a 40% swing phase [28]. Furthermore, during a typical gait cycle, maximal knee extension in the stance phase appears during mid-stance and maximal hip extension appears during the terminal stance phase [28]. HAL-SJ training improved the maximum angles of the hip and knee joints similar to the joint angle curve of a typical gait cycle in case 1. The more similar to the typical gait cycle, the less energy that is required for walking [29]. The negative values improved during the swing phase of the ankle joint on the operative side in case 2. The negative value during the swing phase indicated the appearance of drop foot; however, it was improved after HAL-SJ training.

Comment 6.

At times your word choice is not ideal and some sentences need another word to make clearer.  For example, "Furthermore, equinus recurrence may occur in the long term." I suggest changing to "Furthermore, equinus may return over time post-surgery."

Response 6.

Thank you for this suggestion. We have made the necessary changes.

Previous MS. P.11, Line 285-286

Furthermore, equinus recurrence may occur in the long term.^[9]

Revised MS. P.12, Lines 296-297

Furthermore, equinus may develop again over time after surgery [12].

Comment 7.

The first paragraph of the discussion which is potentially the most important has a number of sentences which I can guess what you mean.  As the authors I encourage you to make clearer what you want me to take away from your study.

Response 7.

Thank you for this suggestion. We have made significant changes to the text.

Previous MS. P.11, Line 283-296

Equinus corrective surgery in children is a common and effective treatment.[5-7] How- 283 ever, immediately after surgery to relieve spasticity of the ankle joint, the child's motor 284 function is temporarily reduced.[8] Furthermore, equinus recurrence may occur in the long 285 term.[9] Therefore, postoperative rehabilitation of pediatric equinus is important. FES has 286 been the focus of attention in rehabilitation to improve gait function after pediatric ortho- 287 pedic surgery.[16] Nonetheless, in our clinical treatment, we understood that many chil- 288 dren who experienced FES were afraid of pain and were reluctant to undergo FES treat- 289 ment. Repetitive exercises for ankle dorsiflexion and plantar flexion are very important in 290 rehabilitation after equinus corrective surgery. One of the major problems in the rehabili- 291 tation of children is a lack of sustained concentration. Fear of pain can reduce a child's 292 ability to concentrate and interfere with treatment continuation. HAL-SJ has a BES-based 293 control system and demonstrates joint torque assistance with the wearer’s voluntary drive. 294 HAL-SJ can achieve repetitive ankle dorsiflexion and plantar flexion without strain, which 295 is important for rehabilitation after equinus corrective surgery.

Revised MS. P.12, Lines 294-308

Equinus corrective surgery for children is a common and effective treatment [5, 7]. However, immediately after surgery, the child’s motor function is temporarily reduced to relieve spasticity of the ankle joint [8]. Furthermore, equinus may develop again over time after surgery [12]. Therefore, postoperative rehabilitation for pediatric equinus is important. FES can effectively improve dorsiflexion and plantar flexion [10, 11, 25]. However, FES may be invasive [10]. Furthermore, during our clinical experience, we have found that many children who underwent electrical stimulation, including FES, are hesitant to undergo electrical stimulation because of the fear of pain. However, HAL-SJ training is a non-invasive treatment. Children who have undergone HAL-SJ training can perform repeated ankle dorsiflexion and plantarflexion exercises, which are important for improving postoperative function, without the fear associated with pain. Additionally, HAL-SJ can assist with voluntary ankle dorsiflexion and plantar flexion movements in real time using BES feedback. Furthermore, patients experience neuromuscular motor training and coordination of muscle co-contraction, which may have a motor learning effect. Therefore, the HAL-SJ could be an effective rehabilitation device after equinus corrective surgery.

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper presents two cases of robot-assisted ankle rehabilitation after equinus surgery using HAL-SJ in children.

Although I appreciate the work and effort of the authors, the manuscript requires some significant modifications.

Section 1: Introduction

- References in the text should follow the correct formatting according to MDPI format requirements.

- The contributions and importance of the paper should be highlighted. What are the main advantages of this article concerning other similar works?

Section 2:

- To improve the article structure, you can use the adequate traditional structure of papers for the MDPI journal and use it in many other scientific journals. In this case, I would recommend that Section 2 be named Materials and Methods instead of Case Presentation, which becomes a subsection 2.2.

- I would also recommend that the first subsection, 2.1 present a little of this robotic rehabilitation equipment.

- There is no information about the experiment in the context of Ethical Principles for Medical Research Involving Human Subjects. Patients' consent to conduct the experiments was not indicated. Research of this type requires either the consent of the appropriate bioethical commission or its decision that such a permit is not required.

- The text in Figure 4 does not appear in its entirety, the figure was probably not formatted correctly. Therefore, I recommend reducing the font.

- The title of figure 5 should be written only on one line.

- Also the title of figure 6.

- To make it easier to follow the information in subsection 2.4.3, I recommend that the tables in Figure 7 be placed immediately below the paragraph where they were mentioned.

- Check the formatting of title titles and tables according to MDPI format requirements. They are not respected.

- Line 259 does not follow the format of the text after a table.

- Lines 260-278 are extra because of Integers.

Sectiunea 3:

- This section is missing by skipping directly to Section 4. Section 3 is dedicated to the results obtained, so it will need to be referred to as Results. I would recommend that there are no other results and that subsection 2.4.3 become section 3.

Section 4: Discussions

- Why do the authors consider that the results obtained for only 2 cases are sufficient to validate the general recovery treatment equipment.

- You must also describe the limitations of your study.

Section 5: Conclusion

- What are the future works?

- What are the main challenges of the current work?

 

Author Response

Response to Comments.

Thank you for your comments. We have made changes to improve the manuscript in accordance with your suggestions. The revised parts of the text are shown in red.

Section 1: Introduction

Comment 1.

References in the text should follow the correct formatting according to MDPI format requirements.

Response 1.

Thank you for this suggestion. We have changed the format of references.

Comment 2.

- The contributions and importance of the paper should be highlighted. What are the main advantages of this article concerning other similar works?

Response 2.

Thank you for this suggestion. We have made the necessary changes.

Previous MS. P.1-2, Line 36-72

Equinus is the most common cause of gait disorders in children ^{[1, 2]} and decreases their participation in activities of daily living.^[3] Most childhood equinus cases are caused by central nervous system (CNS) disorders. CNS disorders have both positive and negative features. The positive features include spasticity, clonus, and excessive co-contraction, whereas the negative features include weakness and sensory deficits. The interaction between positive and negative features leads to musculoskeletal pathology (equinus, muscle shortening, and degenerative arthritis). ^[4] Equinus is a substantial problem that needs to be addressed in children with gait disorders.

Conservative treatments such as physical therapy, ankle braces, casting, and botulinum toxin A injections are the treatment of choice for equinus; however, if they are not effective, surgery may be indicated.^{[5, 6]} Orthopedic surgery performed for pediatric equinus, such as equinus correction, is an effective treatment.^[7] However, immediately after orthopedic surgery to relieve spasticity of the ankle joint, correct deformities of the lower limb, and acquire new motor skills, the child's motor function may be temporarily impaired.^[8] Deterioration of function after equinus corrective surgery is caused by weakness of the released muscle and decreased physical fitness as a result of immobility of the operated limbs.^[8] Therefore, after surgery, using the range of motion (ROM) gained in the ankle joint is important to perform repeated dorsiflexion/plantar flexion and standing balance exercises. However, after surgery, pediatric patients will have difficulty performing repetitive movements due to pain, fear, and lack of concentration. Therefore, regaining motor function is difficult, and abnormal gait patterns such as a drooping foot may persist. Bolton et al. have reported that after a mean follow-up of 6.9 years for calf lengthening surgery in children with cerebral palsy, 22% had a recurrence of equinus, and 36% had a recurrence of calcaneus.^[9] This finding illustrates the difficulty and importance of postoperative rehabilitation.

The single-joint Hybrid Assistive Limb (HAL-SJ; HAL-FS01, Cyberdyne, Inc., Tsukuba, Japan) is a wearable robot that can support flexion and extension movements of various joints. The HAL-SJ has a bioelectrical signal (BES)-based control system and demonstrates joint torque assistance with the wearer’s voluntary drive. The HAL-SJ has been used for knee flexion/extension exercises in postoperative total knee arthroplasty patients^[10] and elbow extension-flexion exercises in the spastic cerebral palsy^[11] and has been reported to be effective. In HAL-SJ, a new ankle joint unit has been developed as an accessory that makes it possible to perform ankle joint exercises (Figure 1).

We believe that training pediatric patients with HAL-SJ after equinus corrective surgery would be an enjoyable way to perform repetitive movements without pain or fear. We present two cases of robot-assisted ankle rehabilitation using HAL-SJ in children after equinus surgery.

Revised MS. P.1-2, Lines 44-79

Conservative treatments such as physical therapy, ankle braces, casting, and botulinum toxin A injections are the treatments of choice for equinus; however, if they are not effective, then surgery may be indicated [5, 6]. Orthopedic surgery performed for pediatric equinus, such as equinus correction, is an effective treatment [7]. However, immediately after orthopedic surgery to relieve spasticity of the ankle joint, correct deformities of the lower limb, and acquire new motor skills, the motor function may be temporarily impaired [8]. Deterioration of function after equinus corrective surgery is caused by weakness of the released muscle and decreased physical fitness as a result of immobility of the operated limbs [8]. Therefore, after surgery, the use of the range of motion (ROM) gained in the ankle joint is important to performing repeated dorsiflexion/plantar flexion and standing balance exercises [9]. Furthermore, functional electrical stimulation (FES) has been reported to be effective for improving gait function after pediatric orthopedic surgery [10]. FES provides electrical stimulation via skin surface or implantable electrodes to cause coordinated contraction of skeletal muscles to create goal-directed movement [10, 11]. However, for children, the postoperative recovery of motor function may be difficult to achieve because of pain, fear, and lack of concentration; therefore, abnormal gait, such as drooping foot, may persist. Bolton et al. reported that after a mean follow-up of 6.9 years performed for children with cerebral palsy (CP) who underwent calf lengthening surgery, 22% had recurrence of equinus (dorsiflexion was reduced) and 36% had recurrence of calcaneus (plantarflexion was reduced) [12]. This finding illustrates the difficulty and importance of postoperative rehabilitation.

The single-joint Hybrid Assistive Limb (HAL-SJ) (HAL-FS01; Cyberdyne, Inc., Tsukuba, Japan) is a wearable robot that can support flexion and extension movements of various joints. The HAL-SJ has a bioelectrical signal (BES)-based control system and demonstrates joint torque assistance with the wearer’s voluntary movement. The HAL-SJ has been effectively used for knee flexion and extension exercises performed by patients who have undergone total knee arthroplasty, and for elbow flexion and extension exercises performed by CP patients with spasticity [13, 14]. A new ankle joint unit that makes it possible to perform ankle joint exercises has been developed as an accessory for the HAL-SJ (Figure 1). Ankle rehabilitation using the HAL-SJ has been attempted for adult patients with drop foot, and improvements in muscle activity, strength, and walking speed have been reported [15, 16]. However, the results of the use of the HAL-SJ for pediatric patients who have undergone equinus surgery have not yet been reported. We believe that the HAL-SJ is an effective rehabilitation device for those who have undergone equinus corrective surgery. Therefore, we present two cases of robot-assisted ankle rehabilitation using the HAL-SJ for children after equinus surgery. 

Section 2:

Comment 3.

To improve the article structure, you can use the adequate traditional structure of papers for the MDPI journal and use it in many other scientific journals. In this case, I would recommend that Section 2 be named Materials and Methods instead of Case Presentation, which becomes a subsection 2.2.

Response 3.

Thank you for this suggestion. We have made the necessary changes.

Previous MS. P.3, Line 78.

2. Case Presentation

Revised MS. P.3, Lines 83

2. Materials and Methods

Previous MS. P.3, Line 79 and P.3, Line 92

(Line 79)2.1. Case 1

(Line 92)2.2. Case 2

Revised MS. P.3, Lines 94-95, and P.4, Line 109

(Line 94)2.2. Case presentation

(Line 95)2.2.1. Case 1

(Line 109)2.2.2. Case 2

 

Comment 4.

I would also recommend that the first subsection, 2.1 present a little of this robotic rehabilitation equipment.

Response 4.

Thank you for this suggestion. We have added the details of the robot device.

Revised MS. P.3, Lines 85-93

2.1. The ankle HAL-SJ

The ankle HAL-SJ is a wearable exoskeletal robot that is worn on the outside of the ankle joint and uses actuators that detect BES from the tibialis anterior and gastrocnemius muscles to train the performance of plantarflexion and dorsiflexion. Additionally, light-emitting diodes are built into the joints of the robotic suit to provide visual feedback to the patient and therapist. Assist gain levels range from 0 (unassisted) to 100, thus allowing the controller to adjust the balance between flexion and extension at each level. The controller also has a monitor that displays the BES of the flexor and extensor muscles [15, 16].

Comment 5.

- There is no information about the experiment in the context of Ethical Principles for Medical Research Involving Human Subjects. Patients’ consent to conduct the experiments was not indicated. Research of this type requires either the consent of the appropriate bioethical commission or its decision that such a permit is not required.

Response 5.

Thank you for this suggestion. We have added the ethical considerations.

Revised MS. P.8, Lines 220-227

2.5. Ethical considerations

This study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Ibaraki Prefectural University of Health Sciences (approval number: 797; date of approval: December 28, 2017; approval update: approval number: e356; date of approval: June 8, 2022). Informed consent was obtained in writing from the parents or guardians of the patients involved in the study because they were minors. The research participants were also present during the explanation of the study to confirm their willingness to participate in the study.

Comment 6.

- The text in Figure 4 does not appear in its entirety, the figure was probably not formatted correctly. Therefore, I recommend reducing the font.

Response 6.

Thank you for this suggestion. We have modified Figure 4.

Comment 7.

The title of figure 5 should be written only on one line.

Response 7.

Thank you for this suggestion. We have modified the title of Figure 5.

Previous MS. P.5, Lines 117-119.

Figure 5: HAL-SJ training.

a: Ankle dorsiflexion in sitting position

b: Stepping exercise in standing position

Revised MS. P.6, Line 138-139

Figure 5: Single-joint Hybrid Assistive Limb (HAL-SJ) training: (a) dorsiflexion exercise and (b) stepping exercise.

Comment 8.

Also the title of figure 6.           

Response 8.

Thank you for this suggestion. We have modified the title of Figure 6.

Previous MS. P.6, Lines 158-160.

Figure 6: Wireless inertial measurement Unit (IMU) system

(myoMOTION, Noraxon, USA).

a: Installation, b: Location wireless inertial measurement unit (IMU)

Revised MS. P.7, Line 182-183

Figure 6: Wireless inertial measurement unit (IMU) system: (a) installation and (b) wireless IMU.

Comment 9.

To make it easier to follow the information in subsection 2.4.3, I recommend that the tables in Figure 7 be placed immediately below the paragraph where they were mentioned.

Response 9.

Thank you for your suggestion. We have changed the placement of Figure 7.

Comment 10.

Check the formatting of title titles and tables according to MDPI format requirements. They are not respected.

Response 10.

Thank you for this suggestion. We have checked the MDPI formatting requirements. We hope that they are now suitable.

Comment 11.

Line 259 does not follow the format of the text after a table.

Response 11.

Thank you for pointing this out. We have made the necessary changes.

Comment 12.

Lines 260-278 are extra because of Integers.   

Response 12.

Thank you for this suggestion. We have eliminated all extraneous integers.

Sectiunea 3:

Comment 13.

This section is missing by skipping directly to Section 4. Section 3 is dedicated to the results obtained, so it will need to be referred to as Results. I would recommend that there are no other results and that subsection 2.4.3 become section 3.

Response 13.

Thank you for this suggestion. We have made the necessary changes.

Revised MS. P.8, Line 229

3. Results

Section 4: Discussions

Comment 14.

Why do the authors consider that the results obtained for only 2 cases are sufficient to validate the general recovery treatment equipment.

Response 14.

Thank you for this important question. We found this case report insufficient to validate the efficacy of HAL-SJ. Therefore, we have added a discussion of the limitations of this study and addressed this in our conclusion.

Revised MS. P.13, Lines 363-366

4.1 Study limitations

This manuscript is a case report, and the number of cases is not sufficient to prove the usefulness of HAL-SJ training after equinus corrective surgery. Also, a comparative study with a control group is needed.

Revised MS. P.13, Lines 368-374

HAL-SJ training for pediatric patients after equinus corrective surgery resulted in motor function improvement. However, it is unknown whether the motor function improvement has further effects on the natural course during the postoperative period. Follow-up is necessary to observe the long-term outcomes of patients and determine whether HAL-SJ training has a preventive effect on equinus. Therefore, it is necessary to increase the number of cases and conduct comparative studies with control groups.

Comment 15.

You must also describe the limitations of your study.

Response 15.

Thank you for this suggestion. We have added a discussion of the limitations of this study.

Revised MS. P.13, Lines 363-366

4.1 Study limitations

This manuscript is a case report, and the number of cases is not sufficient to prove the usefulness of HAL-SJ training after equinus corrective surgery. Also, a comparative study with a control group is needed.

Section 5: Conclusion

Comment 16.

 What are the future works?

Response 16.

Thank you for this suggestion. We have addressed this.

Revised MS. Lines P.13, Lines 368-374

HAL-SJ training for pediatric patients after equinus corrective surgery resulted in motor function improvement. However, it is unknown whether the motor function improvement has further effects on the natural course during the postoperative period. Follow-up is necessary to observe the long-term outcomes of patients and determine whether HAL-SJ training has a preventive effect on equinus. Therefore, it is necessary to increase the number of cases and conduct comparative studies with control groups.

Comment 17.

What are the main challenges of the current work?

Response 17.

Thank you for this suggestion. We have addressed this in the conclusion.

Revised MS. Lines P.13, Lines 368-374

HAL-SJ training for pediatric patients after equinus corrective surgery resulted in motor function improvement. However, it is unknown whether the motor function improvement has further effects on the natural course during the postoperative period. Follow-up is necessary to observe the long-term outcomes of patients and determine whether HAL-SJ training has a preventive effect on equinus. Therefore, it is necessary to increase the number of cases and conduct comparative studies with control groups.

Additional Comment

Could you please reduce the similarity rate of the section 2.4 during
revision?

Response.

Thank you for this suggestion. We have changed section 2.4 accordingly.

Previous MS. P.6, Lines 141-146.

The gait analysis used a wireless inertial measurement unit (IMU) system (myoMO-TION, Noraxon, USA) consisting of a receiver and seven IMUs (for the lower body setup) (Figure 6a). Each IMU (37.6 mm × 52.0 mm × 18.1 mm; 34 g) has a local coordinate system and measures accelerations and yaw pitch-roll orientations along three coordinate axes (Figure 6b). IMUs were placed on the body segments according to a rigid lower body model provided by the IMU system software [myoRESEARCH 3.16.86 (MR3)].

Revised MS. Lines P.7, lines 165-172

A three-dimensional gait analysis was performed to determine the joint angles during the gait cycle. A wireless inertial measurement unit (IMU) system (myoMOTION; Noraxon USA, Scottsdale, AZ) consisting of a receiver and seven IMUs (for the lower body) was used for gait analysis (Figure 6a). Each IMU (37.6 mm x 52.0 mm x 18.1 mm; 34 g) had a local coordinate system and measured the acceleration and yaw pitch and roll directions along three coordinate axes (Figure 6b). Each IMU was placed on a body segment according to the rigid body lower body model provided by the IMU system software (myoRESEARCH 3.16.86).

Previous MS. P.7, Lines 117-119.

 Before placing the surface electrodes, the skin surface was wiped with alcohol to re- duce skin impedance. Four bipolar surface electrodes (Noraxon Dual Electrodes, Noraxon USA Inc., Scottsdale, AZ) were attached to the skin of the target muscles. AgCl was used as the surface electrode material, and the distance between the electrodes was 2 cm. The electrodes were placed parallel to the muscle fibers. The sEMG signals were recorded by an Ultium-EMG sensor system (Noraxon USA Inc., Scottsdale, AZ) with a sampling fre-quency of 2000 Hz and a bandpass filter of 20–450 Hz, and finally stored in the computer’s software MR3. A baseline EMG trial was conducted at rest for 1 s in the sitting position. The CoI of the TA and MG muscles was computed during the dorsiflexion to plantar flexion and gait cycle. The CoI was calculated using a customized MATLAB program (MathWorks, Natick, MA, USA). The method used by Chow et al. was used to assess CoI.[15] The average rectified EMG at rest was subtracted from the rectified EMG of the TA and MG muscles. The adjusted EMG was then normalized to the average amplitude of each muscle over the entire gait cycle, and dorsiflexion to plantar flexion. The CoI was calculated from the amplitude-normalized EMG by dividing the area of the TA–MG over- lap by the overlap duration. Since CoI represents the relative magnitude of EMG overlap, the comparison of coactivation between different muscles should be allowed. The CoI takes values from 0 (not co-contraction) to 1 (co-contraction).

Revised MS. Lines P.8, lines 199-218

The skin surface was wiped with alcohol, the skin impedance was lowered, and surface electrodes were placed. Surface electrodes (blue sensor; METS JPN) were placed on the skin of the target muscle. The distance between the electrodes was 2 cm. The electrodes were placed parallel to the muscle fibers. The surface EMG signals were recorded by an Ultium-EMG sensor system (Noraxon USA) with a sampling frequency of 2000 Hz and a bandpass filter of 20–450 Hz. The myoRESEARCH 3.16.86 computer software was used to integrate the surface EMG and three-dimensional gait analysis data. A baseline EMG trial was conducted at rest for 1 s in the sitting position.

The COI values of the tibialis anterior and medial gastrocnemius muscles were computed during the dorsiflexion to plantar flexion and gait cycles. The COI values were calculated using a customized MATLAB program (MathWorks, Natick, MA). The method used by Chow et al. was used to assess the COI values [24]. The average rectified EMG value at rest were subtracted from the rectified EMG values of the tibialis anterior and medial gastrocnemius muscles. The adjusted EMG value was then normalized to the average amplitude of each muscle over the entire gait cycle and during dorsiflexion to plantar flexion. The COI values were calculated from the amplitude-normalized EMG by dividing the overlapping area of the tibialis anterior and medial gastrocnemius by the duration of overlap. Because COI values represent the relative magnitude of myoelectric overlap, it is easy to compare resonances between different muscles. The COI values range from 0 (no co-contraction) to 1 (co-contraction).

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

All observations were respected.