Numerous studies have recently reported applying VR technology in the cervical field, including surgical training, assistance in surgery, rehabilitation, and cervical spine mobility assessment. Chang et al. developed a hybrid device containing a smartphone and virtual reality goggles to examine its reliability and validity in evaluating craniocervical mobility. By wearing such a device, the magnetometer and inclinometer of the smartphone could obtain changes in head posture. This study revealed that this hybrid device exhibited excellent intra-rater intraclass coefficient ≥0.925 and inter-rater intraclass coefficient ≥0.880 when used to assess healthy participants. However, using such hybrid VR devices, the assessment's accuracy is totally dependent on built-in sensors of smartphones, which are inaccurate enough. Also, their recording frequency is insufficient, implying a relatively low frequency of capturing head angle change.
After decades of development, numerous mature products of VR devices are available on the market. Taking HTC Vive (HTC Corporation, Taoyuan, Taiwan) as an example, this kind of VR device uses laser emitters (also called lighthouse) to determine posture and location of device and user. The virtual reality device using lighthouse for positioning has the characteristics of excellent accuracy and high recording frequency. With the help of such a device, the change in craniocervical motion angle can be recorded more accurately while also obtaining more details about the movement process, which can help doctors better understand the whole movement process. Therefore, this study used HTC Vive, an immersive virtual reality device, to accurately record more information.
This study compared reliability and validity of immersive VR devices and universal goniometers in CROM assessment. Our immersive VR technology was demonstrated to be an excellent method for evaluating CROM. Based on measurement data, CROM acquired by VR device was generally similar to that obtained in a previous study conducted by Chang et al.. As a result of our speculation, this inconsistency may be related to different measurement procedures and races of participants, even with different times of measurement.
Our results indicated that Bland-Altman plot revealed a high consistency between immersive VR devices and universal goniometers, for a maximum of only 4 of the 42 paired measurements beyond 95% CI. A significant difference exists between both two methods in left rotation (1.64°, p༜0.001). In Chang's study, they found significant differences between hybrid devices and universal goniometers in left lateral flexion, right, and left rotation. They explained that it is challenging for the goniometer to precisely locate at the head's center, indicating that neck rotation may not occur perfectly at the horizontal plane when measured with a universal goniometer. Compared to a goniometer, an immersive VR device is based on an external laser sensor, and the change of angle is determined by software, which determines that data it provides could accurately reflect the angle changing. As for discrepancies observed in left rotation but not in right rotation, we presumed that they were caused by limitations of goniometer measurement on the one hand and muscle fatigue of subjects while proceeding with the experiment on the other hand.
Besides the great consistency with goniometer, that of VR device itself should be emphasized too.
We observed that while the statistical result of immersive VR device assessment demonstrated remarkable consistency in the intra-rater group, a significant difference in left rotation was revealed (p༜0.013). In inter-rater group, there is a difference between extension (p = 0.028) and right rotation (p = 0.016). The average discrepancy is slight, which is acceptable for clinical evaluation. We speculate that these discrepancies may be associated with measurement methods, particularly the measurement process. Due to the several steps required for measurement, one participant must be measured five times, and neck muscles of participants may become fatigued. As the duration of measurements increases, the craniocervical mobility of participants may decrease. Therefore, we suspect that the assessment process should be perfectly designed. For instance, prolonging the interval between two assessments may be first considered, as this allows the neck muscles of participants to achieve better rest, which is helpful to improve consistency and reliability of measurement.
Apart from immersive VR, non-immersive VR and augmented VR are another two main categories of VR technology. Kiper's research compared CROM measurements taken with immersive and non-immersive VR devices, demonstrating that immersive VR devices could provide more accurate assessment than non-immersive VR devices. In our study, we also found an outstanding ICC demonstrated by immersive VR devices. During measurements, ICC of intra-rater group ranges from 0.885 to 0.978, while ICC of inter-rater group ranges from 0.770 to 0.920. All of them were above 0.750, which was considered good.
Compared with previous measurement methods, using immersive virtual reality technology for assessing head and neck mobility offers more advantages. First, using conventional VR devices, including devices based on smartphones and VR goggles, angular displacement and angular velocity of head and neck in six directions can be detected, which could not be obtained using a goniometer. Simultaneously, by incorporating more advanced external sensors into virtual reality devices, such as lighthouse technology based on laser sensors, displacement and speed of user can be determined. Additionally, immersive VR devices can create a virtual environment that highly simulates the real world. It can provide three-dimensional instructions to subjects during the course of the test. Simultaneously, the immersive scene can make the subjects' visual and vestibular systems receive information, better guiding movement. These characteristics enable the immersive VR technology to assist participants in completing the target task more effectively. Lastly, the immersive VR device could provide a higher frame rate and resolution, reducing nausea and a sense of disequilibrium associated with other devices.
Some limitations should be improved. First, we mainly adopted healthy volunteers from students in medical college, which may introduce selection bias. Second, this study focuses on almost normal, healthy people without neck diseases. As a result, whether this plan could be applied to patients and its effect remain unknown. Third, because VR device we employed is so heavy and the whole procedure is so lengthy, it may cause discomfort to subject's neck. That is why we should investigate subjects' satisfaction with this device and address the weight issue. In addition, during research, we only compared immersive VR devices with traditional universal goniometers; however, there are many plans and devices for measuring CROM. Last but not least, the sequencing of VR and goniometer measurements could result in a potential error; if the goniometer's evaluation was conducted before VR, the final result might be affected to some extent. As a result, we need to conduct additional comparisons between VR devices and those methods to determine the most effective measurement.