Introduction
roprioception is the conscious and unconscious perception of limbs, joint position, sense of movement, and sense of force [1]. Joint proprioception arises from a set of afferent messages from muscle mechanoreceptors, tendons, joint capsules, ligaments, and skin. The receptors involved in proprioception include muscle spindles and the Golgi tendon organ [2, 3]. These muscle-tendon receptors transmit information about the static length of the muscles, the change in muscle length, and the force produced by the muscles to the central nervous system [4]. Given that most of the mechanoreceptors associated with proprioception are active at the end range of motion of a joint, the muscle spindle plays a unique role in transmitting proprioceptive messages [5].
For this reason, static proprioception tests are not practical enough because inactive movements do not stimulate the muscle spindle, which is a very sensitive mechanoreceptor [6]. Studies have shown that after damage to the joint capsule, ligament, labrum, or muscles involved, the proprioception gets impaired [7, 8, 9, 10]. Damage to the tissues that contain mechanoreceptors causes a relative reduction in afferent messages, which can lead to impaired proprioception and make a person prone to re-injury due to a decrease in proprioceptive feedback [11]. Proprioception and vision together play a special role in controlling movements [12]. Therefore, it is imperative to study proprioception to rehabilitate and prevent re-injury [13, 14] properly.
Joint position sense, which is one of the components of proprioception, is a measure of the ability to reproduce a joint angle accurately. This sensation is done actively and passively, and the amount of angle error is a good criterion for measuring the sense of joint position [15]. To measure the joint position sense, various tools and methods, such as electrogoniometer, Biodex machine [16], inclinometer, motion analyzer [17], isokinetic dynamometer [18], and image capture technique [19] have been used. However, these methods are expensive and specialized. Also, they require a lot of space and are unusable in medical settings. Stillman first proposed the image capture technique in 2000 [6]. Unlike other methods, it does not require complex tools and is not limited to use in laboratories. Smith et al., in a review to determine the reliability of knee joint position sense assessment measures, reported good reliability of image capture technique [20]. This technique has been proposed as an acceptable method for measuring the joint position sense of lower limbs [21, 22]. However, few studies have measured the joint position sense of upper limbs by this technique [23, 24]. Olyayi used the image capture technique in a case study and reported its good reliability [23], but for better knowledge, we need a study with a larger sample size. In a review study by Ager et al. on different methods of measuring the sense of active and passive shoulder joint position, the dynamometer showed the highest reliability (0.92), and the image capture technique had the highest reliability (0.81) for measuring the sense of passive shoulder joint position [24]. Because of the differences in the joints of upper and lower limbs, where the lower limbs are for weight-bearing and walking, and the upper limbs are for movement and delicate tasks, studies are needed to evaluate the reliability of image capture technique for the upper limb joints. Therefore, this study aims to evaluate the reliability of the image capture technique for measuring Active Joint Position Sense (AJPS) in upper limbs to be used as an accessible and usable method in clinics.
Materials and Methods
This research is a methodological study. By using a convenience non-probability sampling method, 10 healthy individuals (5 females and 5 males) aged 18-40 years [25]were selected from the students of the University of Social Welfare and Rehabilitation Sciences in Tehran, Iran, in 2019. The sample size was determined according to Relph et al. [21] and using Equation 1. The study process was explained to the participants, and they completed a form containing personal information and signed a consent form to participate in the study. The inclusion criteria were being right-handed (In healthy right-handed people, proprioception in the non-dominant hand is more accurate [25] and no left upper limb injury in the past 6 months [6].


The subjects attended two similar test sessions two days apart. In each session, the AJPS of the left shoulder and elbow was measured through active reproduction of angles and using the image capture technique. The joints were examined in random order, and the participants were asked to guess the order of shoulder or elbow joint measurements without knowing the contents of the sheets in the envelope. To measure each joint, the respective landmarks were first identified with black circular markers (2-cm diameter). Then, a 16-megapixel digital camera was placed at a distance of 1 m and aligned with the joint level.
The measurement of the AJPS of the elbow was done while the patient was sitting on a chair without an armrest and with closed eyes. Elbow landmarks were affixed to the outer edge of the acromion, lateral epicondyle, and between the distal radioulnar joint. The examiner then created the 100-degree angle with a goniometer. After a pause of two seconds, the elbow was returned to its original position, and the participant was asked to reproduce the angle, pause for two seconds, and return to the original position, repeating this maneuver two more times. In each of these steps, a photograph of the angle reproduced by the participant was taken by the camera. The AJPS of the shoulder was measured in the supine position, and the markers were placed on the tip of the ulna and olecranon bones and on both sides of the hands on the bed. The initial position was at 90 degrees angle for the shoulder and elbow; 50 degrees was applied for internal rotation of the shoulder and 30 degrees for its external rotation. The initial angle was measured with a goniometer, and then the participant performed the rotation with their eyes closed, and a photograph of the angle was taken in each repetition. All these steps were done again 2 hours later and 2 days later. Figures 1 and 2 show the active reproduction of the angles for the shoulder and elbow.  At the end of the three phases of evaluation, we imported the relevant photos into the AutoCAD program and obtained the angles by creating line segments from the marker places and connecting them. To obtain the angle reproduction error, the values of absolute error (i.e., the difference between the produced angle and the initial angle without considering the direction of motion) and relative error (i.e., the difference between the produced angle and the initial angle with considering the direction of motion) were calculated [22]. These values for each joint were entered into SPSS v. 19 software. The within-group comparison was performed between the results of the first and second phases to assess intra-day reliability of the test, and a between-group comparison was carried out between the results of the first and third phases to evaluate its inter-day reliability. We used ICC, 95% test power, a significance level of 0.05, and SEM to evaluate absolute repeatability between measurements.
Results
The characteristics of height, weight, and Body Mass Index (BMI) of the participants are presented in Table 1.


The mean and standard deviation of absolute and relative errors obtained from the three measurements are shown in Table 2.


All P values were ≤0.005. According to Shrout’s ICC classification [26], ICC<0.40 indicates poor reliability, 0.40-0.75 indicates moderate reliability, and ICC >0.75 shows excellent reliability. The high ICC for absolute and relative errors in internal and external shoulder rotations and elbow flexion measured in one day indicated that the image capture technique had excellent inter-day reliability to assess AJPS. The high values of ICC for all measurements in several days also indicated the excellent intra-day reliability of this technique. SEM value was also greater than the mean difference in all measurements, indicating absolute repeatability between measurements. Table 3 shows the ICC and SEM values for the measurements.


Discussion and Conclusion
Excellent ICC for relative error (0.9) and absolute error (0.8) of all movements and three measurements indicated high reliability of the joint image capture technique. Olyayi, in a similar study, used the image capture technique by digital camera for the shoulder joint at angles of 30, 45, 65, and 70 degrees while the goniometer was attached to the joint. The obtained results of absolute and relative error of each angle (0.97) showed excellent inter-day reliability of the technique [23]. One of the limitations of their study was its small sample size, which limits the possibility of generalizing the results. Irving et al. compared the reliability of measuring the sense of knee joint position with a goniometer and image capture technique, measured by two examiners in standing position at angles of 20, 40, 75, and 100 degrees. IPad2 was used for taking images, and only one image was taken from each angle, and the participants returned for a second measurement a week later. Their results for the goniometer and image capture technique showed poor to moderate reliability [27]. This result can be related to the long period between two measurements and taking only one picture from an angle [28]. In another study by Relph, the reliability (ICC) of the image capture technique for the knee joint in the sitting and prone positions was reported to be 0.96 by one tester and 0.98 by several testers [21]. For the goniometer, a study reported poor to moderate reliability for measuring the wrist joint position sense at 20 and 45 degrees of extension and flexion, where at 20° flexion angle, it was more reliable [15]. In Dover et al.’s study, an inclinometer was used to measure the AJPS, and a dynamometer was used to measure shoulder force reproduction. They reported very high reliability (0.99). However, they only calculated absolute error [29], while it is better to use relative error because relative error also determines the direction of movement. The inclinometer, like other methods used in studies, has a less clinical aspect.
Few review studies have been performed to find the best measure of the sense of shoulder joint position, which has validated the passive test for the shoulder in the 90-degree abduction and internal rotation [24]. The isokinetic dynamometer has also been suggested as an efficient method for assessing the sense of joint position. Despite low reliability, it allows the evaluation of the cerebral hemispheres in terms of sensorimotor abilities [30]. However, it is not possible to use these facilities in all medical centers. In a study by Juul-Kristensen, the AJPS of the elbow was measured by an electrogoniometer, and the passive joint position sense was measured by the device. The results showed moderate reliability (0.59 and 0.69) for absolute error and poor reliability for variable error of AJPS measured by electrogoniometer [31].
The image capture technique has reliability for measuring the AJPS of the shoulder and elbow. The simplicity and availability of this measurement method make it possible to use it extensively in medical centers and especially in the rehabilitation treatment process to evaluate joint proprioception.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles are considered in this article. The participants were informed about the purpose of the research and its implementation stages. They were also assured about the confidentiality of their information and were free to leave the study whenever they wished, and if desired, the research results would be available to them. Also, this study was approved by the ethics committee of the University of Social Welfare and Rehabilitation Sciences.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
All authors equally contributed to preparing this article.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to thank the participants and Mr. Mohsen Khalifpour for their cooperation. 

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