FormalPara Key Summary Points

Why carry out this study?

This novel assessment device may be cheaper and more accurate in evaluating cervical proprioception compared to the traditional assessment instrument.

Investigations testing the reliability of the novel assessment device in cervical JPE measurement are scarce.

What was learned from the study?

In this study, based on good reliability and validity, we demonstrated that this novel assessment device can be a reliable substitute for the traditional assessment instrument in evaluating proprioception of the cervical spine in certain anatomic planes.

Therefore, the novel assessment device could play a crucial part in building efficiency, improving accuracy, and saving money.

Introduction

Impairment of cervical proprioception is one of the main problems in patients with cervical spondylosis. The cervical proprioceptive system plays a crucial role in controlling posture and maintaining balance [1, 2]. Prior studies have attempted to quantify proprioceptive dysfunction by different methods. Cervical joint position sense (JPS) reflects an individual's ability to recreate and perceive the previous predefined position or ranges of motion of a joint. Thus, the error a person makes when reproducing the predefined target is defined as the joint position error (JPE) [3]. Cervical JPE is one of the practical measures for evaluating cervical proprioception.

Head repositioning to neutral test was selected to quantify cervical proprioception [4]. In the study of head to neutral repositioning test (HRNT), the difference between the initially determined reference point position (neutral or target position) and the position produced when subjects try to match the target position is called JPE and the difference is converted into degrees [5]. Several testing tools, such as cervical range-of-motion device (CROM) [6, 7], single inclinometer [8, 9], goniometer [10], and mobile phone-based joint angle measurement [11] have been studied to measure cervical JPE. Given the well-known drawbacks of expense [12, 13], measurement invariance [14], and the inability of data storage and analysis [15, 16], more and more studies are sought to develop a more accurate and faster instrument for cervical JPE evaluation.

In this study, a novel measuring device, the WitMotion sensor (WS), was developed to assess the cervical JPE. Furthermore, the validity and intra- and inter-rater reliability of the WS in cervical JPE measurement were determined.

Methods

A cross-sectional study with single-group repeated measures was conducted to evaluate the reliability and the validity of the WS and the laser pointer device (LPD). The protocol was granted by the Committee of Ethics of Taizhou People’s Hospital (Code: KY 2022-153-01), and followed the ethical standards of the Declaration of Helsinki. Written informed consent was obtained from the participants for the use and publication of the images.

Participants

In order to have a minimal significant intraclass correlation coefficient (ICC) of 0.60 (1-β = 0.80; α = 0.05), a minimum of 20 participants were needed. Considering possible dropouts from the study, a total of 28 asymptomatic participants (16 women, 12 men; age 25–66 years) were recruited. Participants included were: (1) aged over 18 years old; (2) without cervical spine problem in the last 3 months. The participants with cervical symptoms such as neck pain, stiffness or limitation of motion, confirmed by magnetic resonance imaging, who scored above 10% in the Neck Disability Index (NDI) were excluded [17].

Randomization

The order of measuring participants in each session was randomized using GraphPad software. To avoid possible measurement bias, all measurements obtained are stored in a private Microsoft Excel file and all subjects are not allowed to communicate with each other during the trial.

Variables and Tools

Cervical JPE was assessed by two independent rehabilitation therapists with 5 years of experience using the WS and the LPD in three different planes (sagittal plane: flexion and extension; frontal plane: left and right lateral flexions; transversal plane: left and right rotations).

WitMotion Sensors (WS)

The WitMotion sensors (4 cm × 4 cm × 1.5 cm; weight < 20 g) are attached to the top of the LPD instrument and it integrates high-precision three-axis gyroscope, three-axis accelerometer, three-axis Euler Angle, three-axis magnetic field, high-performance microprocessor, advanced dynamic calculation and Kalman dynamic filtering algorithm. Besides, the WitMotion sensors transmit the data via Bluetooth 2.0 to the upper-computer software, which can record the data, display the range of motion (ROM) simultaneity, and calculate the angle difference between the starting and final positions.

Laser Pointer Device (LPD)

The LPD instrument is a device that attaches a laser pointer to the top of a light headpiece fixed to the head firmly. Also, considering its reliability and universality, the LPD instrument is used clinically widely, although it is not the gold standard to measure cervical JPE [18].

Neck Disability Index

The Neck Disability Index (NDI) is a self-administered questionnaire that is designed to investigate possible cervical discomfort in the subject’s life. Previous studies have reported that the NDI is validated and proved the higher the score, the more serious for the cervical disability [19].

Procedures

Before assessment, each participant was told the information about the experiment and they signed the informed consent form. Subsequently, the cervical JPE of the participant was separately assessed using the WS and the LPD after they completed the NDI scale.

Each participant was required to sit upright at a fixed distance of 90 cm to a target and the target was a white paper (60 × 60 cm) that was glued to the wall and can be adjusted according to the height of the participants. Next, the LPD that binds the WS was placed on the participants' heads (Fig. 1A). Meanwhile, all participants wore blindfolds to block visual interference and were strapped across the shoulders to the chair to reduce limb compensation. Then, the examiner asked the participant to move their head from the neutral position into approximately 50% of maximal cervical range of motion and then slowly return the head to the neutral position after holding for 3 s.

Fig. 1
figure 1

Simultaneous measurement of the WitMotion sensors and the laser pointer device. A Proprioceptive tests; B The upper computer software

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The initial and final position of each measurement was marked in the white paper and the distance between the two locations is recorded. Based on the values of the absolute distance, the cervical proprioception was quantified by calculating cervical JPE using the formula [20, 21].

$$\Theta = {\text{ tan}}^{{ - {1}}} \left( {{\text{error distance}}/{9}0{\text{ cm}}} \right)$$

For the sensor, the angle of the initial position and the final position is recorded and the trajectory of each direction is displayed on the upper computer (Fig. 1B).

All participants were measured three times consecutively, and a 1-min break was given between the two tests. After evaluation of rater A, rater B repeats the measurements in exactly the same manner. To determine the intra-rater reliability, rater A measured the JPE again in the same conditions 7 days later.

Statistical Methods

Statistical analysis was performed using SPSS software (version 25.0). Reliability is analyzed by calculating intraclass correlation coefficient (ICC), two-way random and absolute agreement, and its 95% confidence interval. The single and averaged measurements are described as ICC[2,1] and ICC[2,2], according to the ICC model. In this study, we determine the averages of three consecutive measures of the rater A and which were used to calculate the ICC of the intra-rater reliability by comparing ICC before and after 7 days. For the ICC of inter-rater reliability, it is calculated by measuring the averages of three consecutive measures of each rater. According to previously published categories, the ICC was interpreted to the level: < 0.40 is poor agreement, 0.40–0.75 is moderate agreement, > 0.75 is good agreement, and ≥ 0.90 is excellent agreement [22]. Finally, the validity (the WS vs. the LPD) was determined by analyzing the ICC and the Spearman’s correlation between rater A and rater B. Based on the results of a study, the correlation size was considered as negligible (0.00–0.30), low (0.30–0.50), moderate (0.50–0.70), high (0.70–0.90), or very high (0.90–1) [23].

The standard error of measurement (SEM) and the minimum detectable change at the 90% confidence interval (MDC90) were used to assess measurement error for both reliability and validity. The following formula (1) was used to calculate the SEM and formula (2) was used to calculate the MDC90.

$${\text{SEM }} = {\text{ SD}}*\surd \left( {{1} - {\text{ICC}}} \right)$$
(1)
$${\text{MDC9}}0 = {1}.{65}*{\text{SEM}}*\surd {2}$$
(2)

Bland–Altman is a visual display method plotting a scatter diagram to visualize the deviation of each pair of values of each subject. The limits of agreement (LoA) of the two measurement results were calculated using mean differences ± (standard deviation × 1.96).

Results

Intra-rater Reliability

Moderate-to-good ICC for all measurements (ICCs > 0.507) made by rater A are shown in Table 1. For the LPD instrument, moderate intra-rater reliability was observed in cervical flexion, left rotation, and right-lateral flexion (ICCs = 0.512–0.719), while good intra-rater reliability was represented in extension, left lateral flexion, and right rotation (ICCs = 0.767–0.796). Meanwhile, the WS showed moderate intra-rater reliability results in extension, right rotation, left-lateral flexion, and right-lateral flexion (ICCs = 0.507–0.682) and good intra-rater reliability was represented in flexion and left rotation (ICCs = 0.757–0.774). Regarding the SEM analysis, the rater A reported a SEM ≤ 1.644 and ≤ 1.590 with the LPD instrument and the WS, respectively. Also, an MDC90 range of 1.925–3.835 for the LPD instrument and 1.768–3.709 for the WS are presented in Table 1.

Table 1 Intra-rater reliability
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Inter-rater Reliability

For the inter-rater reliability analyses, we found it was good to excellent for the LPD in cervical flexion, right-lateral flexion, and left-rotation and right-rotation (ICCs = 0.859–0.950), but results were moderate in cervical extension, left-lateral flexion (ICCs = 0.712–0.727). Reliability for the WS was good to excellent in cervical flexion, right-lateral flexion left-rotation and right-rotation (ICCs = 0.770–0.920), but moderate in cervical extension and left-lateral flexion (ICCs = 0.580–0.679). Meanwhile, the values of SEMs were ≤ 2.664 and ≤ 1.538 for the LPD instrument and the WS, respectively. In regard to the MDC90, it was measured between 1.168 and 2.293 for the LPD instrument and between 1.826 and 3.589 for the WS (Table 2).

Table 2 Inter-rater reliability
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Criterion Validity

Validity was assessed by Spearman’s correlation and intra-class correlation coefficient (ICC) in combination with assessment of systematic bias. We observed good-to-excellent validity for the movements of cervical flexion (ICC = 0.869; r = 0.880, p < 0.001), cervical extension (ICC = 0.786; r = 0.806, p < 0.001) and right-rotation (ICC = 0.860; r = 0.876, p < 0.001). Moderate validity was observed in cervical left-rotation (ICC = 0.622; r = 0.632, p < 0.001) and left-lateral flexion (ICC = 0.614; r = 0.668, p < 0.001) and right-lateral flexion (ICC = 0.709; r = 0.724, p < 0.001). Regarding the SEM analysis, it is reported ≤ 1.947 for rater A and the MDC90 range from 2.120 to 4.544. The complete results are presented in Table 3.

Table 3 Validity of the WS compared to the LPD
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Furthermore, the Bland–Altman plots and the 95% LoA (Figs. 2, 3, and 4) show strong consistency between the two instruments according to the fact that most of the points were distributed between the upper and lower agreements. Especially, the most consistency was observed by the comparison between the LPD and WS when assessing cervical rotation.

Fig. 2
figure 2

Bland–Altman plot detailing the comparison between the LPD and WS when rater A was assessing cervical flexion (A) and cervical extension (B). The red line (middle one) indicates the mean difference. Black lines (extremities) indicate upper and lower agreements. LPD universal instrument; WS WitMotion sensor

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Fig. 3
figure 3

Bland–Altman plot detailing the comparison between the LPD and WS when rater A was assessing cervical left lateral flexion (A) and cervical right lateral flexion (B). The red line (middle one) indicates the mean difference. Black lines (extremities) indicate upper and lower agreements. LPD universal instrument, WS WitMotion sensor

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Fig. 4
figure 4

Bland–Altman plot detailing the comparison between the LPD and WS when rater A was assessing cervical left rotation (A) and cervical right rotation (B). The red line (middle one) indicates the mean difference. Black lines (extremities) indicate upper and lower agreements. LPD universal instrument, WS WitMotion sensor

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Discussion

In clinical practice, the patients with neck pain are usually accompanied by impaired proprioception [18]. In addition, the treatment with targeted rehabilitation exercises can be determined only when cervical proprioception is evaluated accurately. Therefore, the assessment of cervical proprioception as an objective and repeatable assessment method was widely used to examine the degree of cervical impairment and effectives of cervical rehabilitation exercise. In a randomized controlled trial, Jull et al. [24] assessed JPE in patients with chronic neck pain. Then, it revealed that the proprioceptive training group had a greater improvement in reducing cervical JPE and neck pain compared to the control group. In another cross-sectional study, Zeng et al. [25] explored a simple, objective, and more reliable assessment method to quantify cervical dysfunction of patients with cervical spondylosis myelopathy (CSM). It demonstrated that the analysis of dynamic cervical spine motion (ADCM) could provide cervical dynamic parameters for evaluating the severity of CSM patients roundly. In the present study, we examined the reliability and validity of the WS for evaluating cervical proprioception in three different planes. Furthermore, the study focused on measurements of the cervical JPE instead of the cervical ROM, as it was directly related to cervical proprioception in the medical and rehabilitation fields. Moreover, the data of cervical movement could be documented and stored in real time, which makes the WS more meaningful in terms of clinical applications. From the results of the study, we demonstrated that the novel device can be an alternative tool for evaluating cervical proprioception in clinical practice.

Reliability is usually analyzed before a novel instrument or research method is applied in practice [26]. According to previous literature, ICC scores ranging from 0.75 to 0.90 are labeled as good, and those above 0.90 are described as excellent [22]. For the intra-rater reliability, several studies have analyzed it in assessing CROM with inertial sensors. In a study by Gobbo et al. [27], the intra-rater reliability of an integrated inertial sensor (IIS) had moderate-to-good agreement in older adults (OA) and younger adults (YA), which is consistent with this study. It should be noted that our study aimed to measure cervical JPE rather than cervical ROM, because cervical JPE is directly related to cervical proprioception. Given the LPD, the intra-rater reliability of cervical JPE was moderate to good, which seemed to be consistent with the results of the study by Gonçalves et al. The difference was that Gonçalves et al. assessed the reliability, measurement error, discriminative validity, and convergent validity of four proprioceptive tests in individuals with chronic idiopathic neck pain and asymptomatic individuals [28].

With respect to the SEM and MDC, both the LPD and the WS showed low values of SEM and MDC in our study, which means a greater accuracy of absolute reliability. In this study, a 1-week second-measurement time was chosen to avoid a flashback of the participants' memory and reduce external effects. Thus, the WS can be considered as a substitute for evaluating cervical proprioception based on the high intra-rater reliability and low values of SEM and MDC simultaneously.

In relation to inter-rater reliability, prior studies have also analyzed it in using inertial sensors to assess cervical CROM and the results obtained was moderate to excellent (ICCs > 0.75) [27, 29]. A study by Anoro et al. [30] provided the value of MDC90 and SEM, which is beneficial to analyze the effect of measurement error on research results. Similarly, the results of inter-rater reliability for the WS in this study is closer to the results of prior studies although the cervical JPE was evaluated instead of cervical ROM (ICCs = 0.518–0.920; 95% CI 0.176–0.962). Furthermore, the low values of SEM and MDC presented in Table 2 suggest that the WS can evaluate cervical JPE and also detect the changes from actual cervical JPE because of the therapeutic interventions.

Based on the results of this study, we can find the level of inter-rater reliability of the LPD is similar to that of the WS, except in right lateral flexion, for which the LPD showed excellent reliability, otherwise it is moderate to the WS.

To our knowledge, there were no studies analyzing the validation of sensors for measuring cervical JPE. Therefore, we analyzed it in this study and it was presented moderate to good (ICCs = 0.513–0.869) when we compared the results obtained by the WS with those recorded by the LPD. It should be mentioned that the difference in the WS and the LPD varied from 1.08° to 6.39° of cervical movement for all directions based on the 95% LoA. The lower values of the validity observed in the movements of lateral flexion (ICCs < 0.60) may partly be explained by the fact that it was sensible to electromagnetic fields. This may lessen the accuracy of measurement.

The validity of sensors for measuring cervical ROM have been reported in previous studies. For instance, in order to measure more accurate CROM, Raya et al. [29] used two hardware sensors to reduce back compensation and compared the values measured by an optoelectronic system, which is considered the gold standard for cervical ROM [31]. Also, Ignacio et al. [32] analyzed the validity of inertial sensors and the cervical ROM instrument for measuring active CROM in patients with chronic primary headache. The ICCs were moderate for both raters (ICCs > 0.70), which were consistent with the results of this study.

In consideration of the limitations of this study, first, the validity for measuring cervical JPE by WS was not compared with that of the cervical CROM instrument. However, this study aimed to compare the reliability and the validity of this novel instrument with that of the LPD. Also, there are few studies on the validity of sensors. Second, this study was limited by the absence of the participants with neck pain, therefore further studies in subjects with neck pain would be more convincing in assessing the reliability and validity of cervical JPE by the WS instrument. Third, this study did not explore the effect of sensor placement on the evaluation results. Further studies can determine whether the measurement results of sensors placed on the top of the head are consistent with those of sensors placed on the forehead.

Conclusions

The results of this investigation showed that the intra- and inter-reliability and validity was moderate to excellent. Therefore, based on our results plus its inexpensiveness and accuracy, the WS can be a reliable substitute for the LPD to evaluate proprioception of the cervical spine in certain anatomic planes.