
==== Front
Eur J Phys Rehabil Med
Eur J Phys Rehabil Med
EJPRM
European Journal of Physical and Rehabilitation Medicine
1973-9087
1973-9095
Edizioni Minerva Medica

38922315
8115
10.23736/S1973-9087.24.08115-2
Article
Sensory-motor training with virtual reality as a complementary intervention to manual therapy for persistent non-specific neck pain: a randomized controlled trial
EMEDOLI Daniele 1 2 *
ALEMANNO Federica 1
IANNACCONE Sandro 1
HOUDAYER Elise 1
CASTELLAZZI Paola 1
ZANGRILLO Federica 1
GASPEROTTI Filippo 1
LOCATELLI Matteo 1
TETTAMANTI Andrea 1 2
1Department of Rehabilitation and Functional Recovery, IRCCS San Raffaele Hospital, Milan, Italy; 2Vita-Salute San Raffaele University, Milan, Italy
* Corresponding author: Daniele Emedoli, Department of Rehabilitation and Functional Recovery, IRCCS San Raffaele Hospital, via Olgettina 60, Milan, Italy. E-mail: emedoli.daniele@hsr.it
Authors’ contributions: Daniele Emedoli: conceived the idea for the study; contributing to the conception, design, analysing and interpreting data; drafting the article and revising it critically for important intellectual content; approving the final version to be published. Sandro Iannaccone: drafting the article and revising it critically for important intellectual content; approving the final version to be published. Federica Alemanno: approving the final version to be published. Elise Houdayer: drafting the article and revising it critically for important intellectual content; approving the final version to be published. Paola Castellazzi: approving the final version to be published. Federica Zangrillo: drafting the article and revising it critically for important intellectual content; approving the final version to be published. Filippo Gasperotti: drafting the article and revising it critically for important intellectual content; approving the final version to be published. Matteo Locatelli: contributing to the conception, design, analyzing and interpreting data; drafting the article and revising it critically for important intellectual content; approving the final version to be published. Andrea Tettamanti: contributing to the conception, design, analyzing and interpreting data; drafting the article and revising it critically for important intellectual content; approving the final version to be published. All authors read and approved the final version of the manuscript.

28 8 2024
8 2024
60 4 680690
15 5 2024
15 4 2024
27 6 2023
2024 THE AUTHORS
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (CC BY-NC-ND) 4.0 License.
BACKGROUND

Persistent non-specific neck pain (NP) is a widespread condition described as a complex biopsychosocial disorder, characterized by physical and psychological symptoms. Virtual reality (VR) shows promise in NP treatment, potentially reducing pain, kinesiophobia, and improving range of motion (ROM) and motor control.

AIM

The primary aim of the study was to assess the effectiveness of VR sensorimotor training, combined with manual therapy, in reducing the level of disability in persistent non-specific NP individuals. The secondary aim was to determine if this VR-enhanced approach also contributes to improvement in overall function, pain perception and kinesiophobia.

DESIGN

Monocentric, single-blind, randomized controlled trial.

SETTING

We conducted this trial at San Raffaele Scientific Institute, Department of Rehabilitation and Functional Recovery, Milan, Italy.

POPULATION

Forty NP participants were enrolled in the study and randomly allocated into two groups.

METHODS

The study involved a 6-week rehabilitation program, comprising 12 sessions of 45 minutes each, twice weekly. Both intervention groups underwent manual therapy as a consistent component of their treatment. The Experimental Group (VRT) was additionally engaged in sensorimotor rehabilitation exercises using Virtual Reality, whereas the Control Group (CT) performed the same exercises without VR. We assessed subjects at baseline (T0) and after six weeks of rehabilitation (T1). The primary outcome was the disability (Neck Disability Index) while the secondary outcomes were: pain perception (Numeric Rating Scale, NP and Disability Scale, Central Sensitization Inventory) function (Cervical Kinematics) and kinesiophobia (Tampa Scale of Kinesiophobia).

RESULTS

Both groups demonstrated significant reduction in level of disability, pain perception, and kinesiophobia. Significant advancements in kinematics were observed: VRT group showed enhanced ROM during craniocervical rotation (P=0.039), lateral bending (P=0.001), flexion-extension (P=0.009), and mean velocity across movements (P<0.001), whereas CT group improved in maximal ROM during lateral bending rotation (P=0.001). Between-group analysis, after Bonferroni’s correction for multiple comparisons, revealed that VRT group had significantly better outcomes in ROM during rotation (P=0.040), ratio of the primary over the secondary movement while performing rotation (P=0.021), and mean velocity during lateral bending (P=0.031).

CONCLUSIONS

Sensorimotor training, combined with manual therapy, could enhance kinematic outcomes for NP patients, supporting the potential of VR in rehabilitation.

CLINICAL REHABILITATION IMPACT

This study highlighted that both groups demonstrated significant reduction in level of disability, pain perception, and kinesiophobia after sensorimotor training combined with manual therapy. It is important to underscore that in terms of reducing the level of neck disability, both interventions proved to be equally effective. This parity in efficacy is a critical finding, reaffirming the robustness of our therapeutic approaches for this specific outcome.

Key words:

Neck pain
Chronic pain
Virtual reality
==== Body
pmcNeck pain (NP) is described as discomfort or more intense form of pain localized to the cervical region. Non-specific NP is defined as pain in the posterior and lateral aspect of the neck between the superior nuchal line and the spinous process of the first thoracic vertebra, with no signs or symptoms of specific structural pathology and with the absence of neurological signs.1

Many patients experience NP as a complex biopsychosocial disorder, characterized by physical and physiological symptoms, leading to chronic disability.2

Therapeutic exercises have been studied during years supporting the idea that therapies involving exercise are effective in combination with mobilization and manipulation for the management of NP.2 Recent studies demonstrated also that information and education for NP subjects are effective and are an essential part of the therapy.3 Also, in this population, cervical conjunct motion has been studied over the years, consisting in cervical movements in the associated planes relative to the primary movement plane. When cervical conjunct motion is reduced, it may reflect protective strategies of postural control or adaptations in the central nervous motor processing due to long-standing pain.4-7 The field of neck kinematics in the presence of persistent pain has been deeply investigated and, thanks to these studies, impairments in cervical movement kinematics, such as reduced movement accuracy, velocity, smoothness and head stability have been identified.8-10

Cervical motion can be assessed through Virtual Reality (VR) systems, combined with wearable sensors and the use of visual stimuli that might induce spontaneous neck motion.11-13 This methodology seemed to be more reliable and sensitive than conventional ROM assessment.14 VR also constitutes a technological rehabilitation tool that allows the user to experience and interact with a computer-generated environment, which provides several advantages over standard care. VR allows the simulation of realistic environments, real-life exercises and activities that could be personalized to meet the specific needs of the patient, providing distraction by shifting the attention from pain to external stimuli. Generally, patients feel more motivated by this kind of virtual environment,15 which is an important factor that could influence rehabilitation and performance outcome.16

VR devices can be categorized in fully-immersive, semi-immersive and non-immersive, based on the level of immersion, on desired stimulated physiological sense, degree of interaction with VR environment and isolation of the users from the external environment.17-19 Through these modalities, the patient is able to perceive visual, auditory, tactile or kinesthetic stimuli in a virtual world.20 The exposure of VR can seldom lead to symptoms such as visual fatigue, headache, nausea, dizziness or cybersickness that is described as the feeling of discomfort due to mismatch between observed and expected sensory signals.21-23

A meta-analysis published in 2019 showed that VR applied to patients with NP was promising in producing positive effects when applied alone or combined with therapeutic exercises, concluding that future clinical studies are necessary to reach more solid conclusions.24

Here, with our study we aimed to assess the effects of a VR-sensorimotor training on disability in persistent NP patients in addition to manual therapy treatment.

The secondary aims were to assess if VR-sensorimotor training could improve also Function, Perception of Pain and Kinesiophobia, compared to sensorimotor training without VR, in NP individuals.

Materials and methods

Study design

This study was a monocentric, single-blinded, randomized controlled trial. We enrolled forty participants suffering from persistent NP and we randomly divided them, by an independent person who was not involved in the recruitment, intervention or assessment, into: 21 subjects for the experimental group (VRT) and 19 subjects for the control group (CT). We conducted recruitments, training sessions and assessments at the IRCCS San Raffaele Hospital, Department of Rehabilitation and Functional Recovery (Milan, Italy), from June 2019 to May 2022. Seven patients dropped out (four from the VRT group, three from CT group). One drop-out occurred for family related health reasons and impossibility to continue the training and six drop-outs occurred from February 2020 to June 2021 due to Covid-19 pandemic reasons (Flow chart of the study into result section). A blinded investigator executed a block randomization through a digital software and applied a stratification by age (range: 18-35, 36-50, 51-70). In order to anonymize all data, an alphanumeric code was assigned to each patient. A blind investigator wrote the group allocation on a card inside an opaque sealed envelope ordered in progressive numbers, locked in a closet locker and the blind investigator gave them progressively to the physiotherapist who managed the treatments. The researcher who performed all assessments was blinded to treatment allocation. Due to the nature of the intervention, participants and physiotherapists providing the training intervention could not be blinded to treatment allocation. Participants were also explicitly asked to not disclose group allocation to the researcher who performed assessments. The assigned intervention was only granted for the researcher when it was necessary to manage serious adverse events, which never happened in this study.

The protocol of the study has been approved by the Ethics Committee of San Raffaele Hospital and it is registered in clinicaltrials.gov (NCT03987334). The study has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki. All participants provided written informed consent prior to inclusion in the study.

Participants

We included participants if they met the following inclusion criteria: 1) 18-70 years old individuals with persistent NP (≥12 weeks), with 2) pain located in the posterior and/or lateral aspect of the neck between the superior nuchal line and the spinous process of the first thoracic vertebra (assessed through body chart) and with 3) normal vision or corrected using contact lenses or eyeglasses. Exclusion criteria for this study were: 2) informed consent negation, 2) systemic infection, 3) metabolic/neurological/muscular degenerative disorder, 4) cervical spinal pathology, 5) fracture or surgery, 6) radiculopathy, 7) vestibular impairments, 8) epilepsy, and 9) pregnancy.

Recruitment and consent

Physicians and physiotherapists primarily recruited participants providing a brief description of the study to the patients. If patients were interested, the researcher then contacted them and gave further information about the study. If subjects were willing to participate, written informed consent was obtained and patient details were given to an independent person for randomization. During the first evaluation all the inclusion criteria have been verified by a physician. All participant provided informant consent, and anonymity was assured.

Intervention

Forty persistent NP subjects received 12 rehabilitation treatments, twice a week, for six consecutive weeks. Each session lasted 45 minutes. The first 15 minutes of treatment consisted, for each group, in manual therapy treatment, such as mobilization and trigger-points treatment tailored on the individual. Then subjects in the VRT group underwent 30 minutes of motor control exercises using a VR-based sensorimotor rehabilitation provided using the Virtual Reality Rehabilitation System (VRRS) of Khymeia Group.25 The VRRS allowed the participant to perform the requested motor tasks, while the movement of the system’s end-effector was simultaneously represented in a virtual scenario. CT patients performed the same exercises of the VR group in terms of intensity, time and type but without using the VR system. Therefore, patients of both groups performed exactly the same treatment, by only differing in the presence of the augmented feedback provided by VR environment. Through randomization of the sample, any potential differences in manual treatment approaches were distributed across both study groups, minimizing their impact on the results.

In addition, all subjects were educated in emphasizing self-management and return to normal function.26, 27 Participants were asked not to undergo other rehabilitation treatment for their NP during the study. We evaluated the subjects at baseline (T0) and after six weeks of rehabilitation (T1). To promote participant retention, we planned training sessions in consultation with the participants and they were also informed timely about the entire training schedule and assessments.

Experimental group rehabilitation

Experimental group performed, after the first 15 minutes of manual therapy, 30 minutes of sensorimotor training, provided by real time augmented feedback on VR focused on motor control. Two Inertial Measurement Unit sensors (IMU) were placed on the patient’s forehead and on the manubrium of the sternum. Each subject was able to observe the position of the sensors projected as feedback on the screen of the VRRS system. Training provided to the VRT group focused especially on active ROM exercises with different scenarios (Figure 1).

Figure 1 —Flow chart of the study.

The exercises were divided into: 1) simple exercises on only one plane of movement, 2) advanced exercises introducing multiplanar movements, 3) motor control exercises by “drawing” geometric figures with the head (with the possibility of checking instantaneously the trace of movement drawing), 4) focus shifting exercises (mismatching the effects of feedback and the movement of the head), and lastly 5) game-based exercises (Supplementary Digital Material 1: Supplementary Figure 1, Supplementary Text File 1).

Control group rehabilitation

CT group performed, after the first 15 minutes of manual therapy, 30 minutes of sensorimotor training with therapist.28-30 The training program of the CT group was equivalent to the VRT group and consisted of: 1) simple exercises performed on one plane of movement (cranio-cervical flexion and extension, rotation, lateral bending movements), 2) advanced exercises composed of multiplanar movements and 3) motor control exercises focused to “draw in air” some requested geometric figures, letters or numbers with head movements and to perform active movements in the three main planes changing the velocity, as asked by the therapist.31

Outcome variables

During the baseline assessment, we evaluated several variables. An overview of the measurement used to assess the primary and secondary outcome variables is given in Supplementary Digital Material 2 (Supplementary Table I).

Primary outcome

The primary outcome was the Neck Disability Index (NDI), which measured the effects of the intervention on level of disability in NP subjects.32 The NDI is a self-reported questionnaire used to determine how NP affects a patient’s daily life and to assess the self-rated disability of patients with NP. The NDI consists of 10 questions in various domains: Pain Intensity, Personal care, Lifting, Reading, Headaches, Concentration, Work, Driving, Sleeping and Recreation. Each question contains six answer choices, scored from 0 (no disability) to 5 (complete disability). Total score is reported on a 0-50 scale but it can also be reported from 0-100, where higher scores indicate greater disability.33, 34 The NDI showed good validity and reliability: changes should exceed the MCID of 3.5 points’ cut-off to be considered relevant.35

Secondary outcomes

As secondary outcomes, we evaluated the Pain Perception (Numeric Rating Scale [NRS],36 Neck Pain and Disability Scale [NPDS],37 Central Sensitization Inventory [CSI]),38 Function (Cervical Kinematics) and Kinesiophobia (Tampa Scale of Kinesiophobia [TSK]).39

The NRS is a segmented numeric horizontal bar on which patients select a whole number (from 0: “no pain” to 10: “worst possible pain”) that best reflects the intensity average of their pain at rest and on movement in the previous weeks. It has become a widely used instrument for pain screening in many health care environments.36

The NPDS is made by 20 items and measures the intensity of pain and its interference with vocational, recreational, social and functional aspects of living and the presence and extent of associated emotional factors. Each item scores range from 0 to 5, where higher scores are associated with greater disability.40

The CSI was designed as a screening instrument to identify if a patient’s symptoms may be related to central sensitization. Its score ranges from 0 to 100 and a cut-off score of 40 is considered to identify >82% of central sensitization pain patients, and 32.8% of NP patients exceed this cut-off.41

The TSK is a 17-item self-completed questionnaire used to assess the subjective rating of kinesiophobia or fear of movement. The Italian version range of scores are from 13 to 52, where higher scores indicate an increasing Kinesiophobia.42, 43

Kinematic outcome variables

We measured cervical function with Polhemus G4 electromagnetic tracking system (Polhemus, VT, USA) by placing two sensors on the subject’s forehead and sternum. The system reliably tracks head position and cervical range of motion among asymptomatic subjects as well as persistent NP patients.44-46 To prevent interference of the magnetic field, we removed all ferromagnetic materials from the research area and participants.47 We positioned the transmitter at a distance of 75 cm, in front of the subject, at a high of 80 cm from the floor. The manufacturers report a static accuracy of 0.76 mm rms and 0.15-degree rms within 762 mm of the source.48

We positioned subjects on a plastic chair and we instructed them to hold an upright position of their spine during the whole procedure. A customized acquisition console developed ad-hoc recorded cervical movements, registering position coordinates and rotational matrices. We removed thoracic motion from the cervical ROM subtracting the angular orientation of the sternum sensor from the forehead sensor.

Eight active cervical planar movements in each cardinal plane (four each side), composed the evaluation procedures: four axial rotation right-left, 4 lateral bending right-left, 4 flexion-extension. We instructed subjects to perform plain movements at their own comfortable speed, encouraging the subject to perform maximal movements without feeling pain. We acquired raw data from cervical kinematics and we analyzed post-processing by a specific customized algorithm for detection and quantification of Range of Motion, angular velocity, ratio between movements, acceleration and other parameters using Matlab (The Math Works Inc., Natick, MA, USA). Supplementary Digital Material 3 (Supplementary Figure 2, 3) gives explanation of sensors’ axis relative to cervical movements and algorithm details.

Sample size calculation

Considering the Neck Disability Index mean difference between the two groups as a change of 3.8 points and standard deviation of 2.83,49 5% type I error (α=0.05), 90% power (β=0.1) we established a targeted sample size of 30 participants, 15 each group, suffering from persistent non-specific NP. Due to the drop-outs occurred during COVID-19 pandemic, we recruited a total of 40 NP patients.

Statistical analysis

Therapist assessed all the patients, independently of their compliance with the treatment, with the aim to perform an intention to treat analysis. If a patient interrupted the treatment protocol, the subject was asked to perform the post-treatment assessment even so.

The 6-weeks of training could be interrupted for a maximum period of 2 weeks. The possible causes of interruption could be illness or holidays.

We performed data analyses using RStudio statistical software (version 1.4.1717), summarizing demographics and baseline data with statistics (mean and standard deviation, median and quartiles) or with frequency distributions (baseline data are available in Supplementary Digital Material 4: Supplementary Table II).

We assessed data distribution using the Shapiro-Wilk Test, applying non-parametric tests to analyze data, evaluating within and between groups longitudinal changes (T0-T1) using linear mixed-effects models and adjusting such models for the baseline value of each considered variable. We also applied the Bonferroni’s correction for multiple comparisons.

Data availability statement

The data associated with the paper are not publicly available but are available from the corresponding author on reasonable request.

Results

Forty participants suffering from persistent NP were enrolled and randomly divided into: 21 subjects for the experimental group and 19 subjects for the control group (Figure 2).

Figure 2 —Examples of motor control training of the VRT group.

Baseline comparisons

Participants in both groups were homogenous considering age, pain duration, NDI, NPDS, NRS, CSI, TKS, clinical outcome variables and kinematic outcome variables at baseline. Data are available in Supplementary Table II.

Within group analysis (T0 vs. T1)

Results of the within group analyses about clinical and kinematic outcome variables are summarized in Supplementary Digital Material 5 (Supplementary Table III). At T1 post treatment assessment the VRT group showed significant improvements in: NDI (P<0.001), NRS (P<0.001), NPDS (P<0.001), CSI (P<0.001), TSK (P=0.018), maximum ROM of craniocervical rotation (P=0.039), lateral bending (P<0.001) and flexion-extension (P=0.009), mean velocity of craniocervical rotation (P<0.001), lateral bending (P<0.001) and flexion-extension (P<0.001).

CT within-group analysis found significant differences in the following variables: NDI (P<0.001), NRS (P=0.014), NPDS (P<0.001), CSI (P=0.045), TSK (P=0.005), maximal ROM lateral bending during rotation (P=0.001), maximal ROM ratio rotation/lateral bending during rotation (P=0.001).

Between group analysis (VRT vs. CT)

We summarized results of the between group analysis about clinical and kinematic outcome variables in Table I.

Table I —Results of the between group analysis about clinical and kinematic outcome variables.

Variables	VRT	CT	P value	P value
Bonferroni	
Clinical outcome variables					
Δ %NDI	-16.00
(-18.00; -10.00)
-14.06 (7.00)	-12.50
(-24.50; -6.00)
-14.13 (13.44)	0.820	1.000	
Δ %NPDS	-23.00
(-38.00; -13.00)
-27.94 (21.07)	-14.00
(-32.25; -4.00)
-18.50 (20.16)	0.120	0.232	
Δ NRS	-3.00
(-4.00; -2.00)
-3.00 (1.50)	-1.00
(-5.00; 0.00)
-2.13 (2.73)	0.150	0.300	
Δ TSK	-4.00
(-8.00; -1.00)
-4.12 (7.85)	-3.00
(-5.25; -1.00)
-3.88 (4.57)	0.800	1.000	
Δ CSI	-9.00
(-16.00; -1.00)
-10.18 (12.06)	-8.00
(-13.25; -2.75)
-9.38 (10.11)	0.740	1.000	
Kinematic outcome variables					
Δ Maximal ROM Rotation
during Rotation	4.94
(-0.31; 8.85)
4.65 (11.20)	-5.78
(-10.79; 4.25)
-2.65 (10.95)	0.020	0.040*	
Δ Mean Velocity Rotation
during Rotation	23.22
(17.57; 37.56)
25.34 (20.92)	-2.76
(-15.23; 6.39)
5.89 (51.99)	0.090	0.190	
Δ Maximal ROM Lateral bending
during Rotation	5.48
(-1.12; 7.76)
1.09 (9.34)	8.54
(3.03; 12.99)
7.52 (8.91)	0.040	0.086	
Δ Maximal ROM Ratio
Rotation/Lateral bending
during Rotation	-0.07
(-0.38; 0.32)
0.32 (2.19)	-1.12
(-1.69; -0.65)
-1.44 (2.19)	0.010	0.021*	
Δ Standard deviation Ratio
Rotation/Lateral bending
during Rotation	-0.08
(-0.25; 0.23)
0.65 (3.50)	-1.11
(-1.93; -0.63)
-1.71 (2.87)	0.010	0.033*	
Δ Maximal ROM Lateral bending
during Lateral bending	5.89
(1.63; 8.12)
7.02 (8.68)	2.22
(-3.88; 7.86)
1.65 (9.76)	0.030	0.063	
Δ Mean velocity Lateral bending
during Lateral bending	14.48
(8.45; 25.85)
15.96 (10.20)	-1.26
(-6.11; 4.62)
-0.65 (33.64)	0.010	0.031*	
Δ Maximal ROM Rotation
during Lateral bending	-5.78
(-9.65; 3.16)
-2.29 (14.18)	4.58
(-6.68; 9.06)
2.26 (11.91)	0.310	0.636	
Δ Maximal ROM Ratio
Lateral bending/Rotation
during Lateral bending	0.15
(0.02; 0.43)
0.28 (0.63)	-0.02
(-0.22; 0.27)
0.01 (0.34)	0.070	0.158	
Δ Standard deviation Ratio
Lateral bending/Rotation
during Lateral bending	0.21
(0.07; 0.41)
0.34 (0.79)	0.05
(-0.29; 0.36)
0.03 (0.40)	0.100	0.205	
Δ Maximal ROM Flexion-Extension
during Flexion-Extension	6.35
(0.61; 16.19)
9.35 (11.91)	0.87
(-7.93; 17.62)
6.85 (19.27)	0.490	0.983	
Δ Mean velocity Flexion-Extension
during Flexion-Extension	17.17
(6.34; 28.13)
18.25 (14.69)	-2.41
(-5.50; 7.41)
3.00 (44.91)	0.100	0.215	
Δ Maximal ROM Lateral bending
during Flexion-Extension	3.53
(-1.65; 8.84)
2.57 (15.42)	1.03
(-3.68; 5.66)
3.07 (12.23)	0.970	1.000	
Δ Maximal ROM Ratio
Flexion-Extension/Lateral bending
during Flexion-Extension	-0.99
(-3.93; 2.93)
-0.80 (4.05)	-0.42
(-5.00; 2.05)
-2.69 (10.15)	0.390	0.794	
Δ Standard deviation Ratio
Flexion-Extension/Lateral bending
during Flexion-Extension	-0.95
(-4.61; 6.76)
-0.20 (7.06)	-0.70
(-6.08; 6.49)
0.22 (19.38)	0.840	1.000	
Δ median (first-third percentiles), Δ mean (standard deviation) and P-Value of clinical and kinematic outcome variables in Virtual Reality and Control Groups. VRT: Virtual Reality Treatment, CT: Control Treatment, %NDI: Neck Disability Index, %NPDS: Neck Pain Disability Scale, NRS: Numeric Rating Scale, TSK: Tampa Scale of Kinesiophobia, CSI: Central Sensitization Inventory. *Statistically significant values (P<0.05). In the Clinical Outcome Variables, the numbers with minus sign signify that the post-intervention values are lower than the baseline values, where lower values are associated with reduced Levels of Disability, Pain Perception and Kinesiophobia.

The between-group analysis, after Bonferroni’s correction for multiple comparisons, did not show any statistically significant difference for the clinical self-reported outcome variables (NDI, NPDS, NRS, CSI, TSK), proving that both interventions had similar effects in reducing the level of disability, pain perception and kinesiophobia.

However, VRT group showed a significant between-group difference, after Bonferroni’s correction for multiple comparisons for the following kinematic outcome variables: maximum ROM rotation (P=0.040), ratio of the primary over the secondary movement maximum ROM while performing craniocervical rotation (P=0.021), mean velocity of craniocervical lateral bending (P=0.031).

We also graphically summarized results of within and between analysis into Figure 3 for clinical and kinematic outcome variables.

Figure 3 —Results of clinical and kinematic outcome variables analysis.

Discussion

Previous studies have found that in NP patients, the application of a VR-based neck specific sensorimotor training within a common standard rehabilitation program is both feasible and reasonable.22, 23, 50 This study evaluates the effects of a VR-sensorimotor training in persistent non-specific NP patients, assessing both subjective variables (investigating the level of disability, perception of pain and kinesiophobia) and objective variables (recording different craniocervical kinematics on one or more planes of movement). The study provides a wide number of indicators, some of them have not yet been studied in depth in NP patients’ population.

VRT and CT within-group analysis highlighted that sensorimotor training in persistent NP subjects significantly improved in NDI, exceeding the Minimal Clinically Important Difference of 3.5 points’ cut-off.51 However, the between group analysis did not find significant difference between VRT and CT groups in the aforementioned variable. These findings prove that both interventions, based on sensorimotor training, lead to significant reduction in level of disability. We found similar findings also for pain perception and kinesiophobia.

After 12 sessions of VR-based sensorimotor training (T1), patients significantly improved in craniocervical kinematic outcome variables, increasing the maximum primary ROM of rotation, lateral bending and flexion-extension, without modifying the ratios of the primary over the secondary movements. Also, craniocervical mean angular velocity during rotation, lateral bending and flexion-extension significantly improved. We attributed those improvements to the fact that during VR-treatment the real-time feedback guided each subject’s craniocervical movements, encouraging patients to reach targets in multiple directions performing maximal ROM without compensatory gestures.

Within-group analysis showed that, in the CT group, primary ROM of rotation, lateral bending and flexion-extension did not significantly change between T0 and T1. Furthermore, we do not find significant improvement in mean velocity during craniocervical movements between T0 and T1. In the CT group, the maximal ROM lateral bending during rotation and the ratio of the primary movement (rotation) over the secondary movement (lateral bending) while performing a rotation significantly decreased over time, showing an increase of the secondary movement over the primary movement. We attributed the reduction of this ratio to the fact that during sensorimotor training without receiving real-time feedback of the performance, patients made more compensatory movements, increasing them variability during cervical gestures.

VR-based sensorimotor training showed a significant between-group difference in maximum ROM rotation and mean velocity of craniocervical lateral bending. We attributed this difference to the fact that VR-sensorimotor training with real time feedback motivated patients, encouraging them to perform maximal craniocervical movements with more confidence than CT training, increasing the perception of safety, reducing pain perception and improving the mean velocity.

Analyzing the ratio of primary movement (rotation) over the secondary movement (lateral bending) while performing rotation, the VRT group showed a constant trend over time whilst the CT group showed a reduction of this ratio (augmented secondary movement compared to the primary). We attributed this between-group difference to the fact that the VR-sensorimotor training permits to maintain the motor control over the coupled movements, while CT sensorimotor training without VR leads to a greater movement’s variability during training.

The VR-augmented feedback regarding the knowledge of result and the knowledge of performance are effective in motor learning.52, 53 It has been found that visual feedback could influence and shape neural activity in motor and premotor cortical areas during motor learning (cortico-cortical interactions), reducing errors during movements54 and the observation of repeated and intentional actions would also facilitate the magnitude of motor evoked potentials.55 Moreover, VR promotes the execution of functional tasks in virtual environments that are similar to real life56 encouraging and promoting the increase of repetitions of the different exercises, as an important factor for motor learning.57 Regarding persistent pain management, in this study VR-sensorimotor exercises provided pain distraction41 by shifting the patient’s focus/attention to highly engaging external stimuli58, 59 in the virtual environment60 and leading to skill building on cervical motor performances.61

Limitations of the study

A study limitation lies in the lack of follow-up visits, which could have helped defining the duration of the effects of sensorimotor training on the clinical and kinematic outcomes.

Conclusions

This study highlighted that both groups demonstrated significant reduction in level of disability, pain perception, and kinesiophobia after sensorimotor training combined with manual therapy. It is important to underscore that in terms of reducing the level of neck disability, which was the primary outcome of this research, both interventions proved to be equally effective. This parity in efficacy is a critical finding, reaffirming the robustness of our therapeutic approaches for this specific outcome. Additionally, the use of augmented feedback has been found to result in statistically significant improvements in functional outcomes for patients with persistent non-specific NP. This innovative technology, when integrated into physiotherapy clinical practice, provides objective evaluations and enables the monitoring of patients’ kinematic changes over time. Such integration represents a promising advancement in the management of persistent NP, offering a nuanced approach that combines traditional manual therapy with technological tools to optimize patient recovery.

Supplementary Digital Material 1

Supplementary Figure 1

Exercises examples. The exercises were divided into: i) simple exercises on only one plane of movement, (ii) advanced exercises introducing more planes of movement, (iiia-b) motor control exercises by “drawing” geometric figures with the head (with the possibility of checking instantaneously the trace of movement drawing) and labyrinth (moving a rolling ball without hitting edges), (iv) focus shifting exercises (mismatching the effects of feedback and the movement of the head), and lastly (v) game-based exercises.

Supplementary Digital Material 2

Supplementary Table I

Outcome variables.

Supplementary Digital Material 3

Supplementary Figure 2

Sensors’ axis relative to cervical movements. Considering the Cardan angles system, the movement of the sensor around Z axis was considered “roll” and corresponded to cervical rotation, the movement around Y axis was considered “yaw” and corresponded to cervical lateral bending and the movement around X axis was considered “pitch” and corresponded to cervical flexion and extension. Primary movement during rotation were associated with lateral bending (secondary movement) and flexion/extension (tertiary movement). Primary movement during lateral bending were associated with rotation (secondary movement) and flexion/extension (tertiary movement), whilst primary movement during flexion/extension were associated with lateral bending (secondary movement) and rotation (tertiary movement).

Supplementary Figure 3

Algorithm details. In the figure is showed the graphical representation of Cervical Lateral Bending (primary movement), Rotation and Flexion/Extension (secondary and tertiary movements) during the cervical lateral bending movement. It is possible to notice the maximal and minimal values of each movement. The algorithm, in order to extrapolate the pure cervical movements, automatically subtract motion from the sensor placed on the sternum to the sensor placed to the forehead and removes the firsts and lasts frames without movements. Then it starts to detect the peak values of each primary, secondary and tertiary movements and the relative’s maximal values, minimal values, means and standard deviations (Figure 4). In addition, ratio between primary and secondary movements and angular velocities have been calculated from the orientation data of the sensors, after a process of sub sequential data filtering with outliers removing.

Supplementary Digital Material 4

Supplementary Table II

Baseline comparisons.

Supplementary Digital Material 5

Supplementary Table III

Results of the within group analyses about clinical and kinematic outcome variables.

Acknowledgements

The authors thank Federico Piron, Marco Pirini and Denis Vidale for assistance and collaboration with engineering development.

Conflicts of interest: The authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.
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