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371

Journal of Sport Rehabilitation, 2016, 25, 371 -379

© 2016 Human Kinetics, Inc. ORIGINAL RESEARCH REPORT

Wellmon, D. Gulick, and Paterson are with the Inst for Physical Therapy Education, Widener University, Chester, PA. C. Gulick is with the Dept of Kinesiology, California State University at Fullerton, Fullerton, CA. Address author correspondence to Dawn Gulick at [email protected].

http://dx.doi.org/10.1123/jsr.2015-0041

Validity and Reliability of 2 Goniometric Mobile Apps: Device, Application, and Examiner Factors

Robert H. Wellmon, Dawn T. Gulick, Mark L. Paterson, and Colleen N. Gulick

Context: Smartphones are being used in a variety of practice settings to measure joint range of motion (ROM). A number of factors can affect the validity of the measurements generated. However, there are no studies examining smartphone-based goniometer applications focusing on measurement variability and error arising from the electromechanical properties of the device being used. Objective: To examine the concurrent validity and interrater reliability of 2 goniometric mobile applica- tions (Goniometer Records, Goniometer Pro), an inclinometer, and a universal goniometer (UG). Design: Nonexperimental, descriptive validation study. Setting: University laboratory. Participants: 3 physical therapists having an average of 25 y of experience. Main Outcome Measures: Three standardized angles (acute, right, obtuse) were constructed to replicate the movement of a hinge joint in the human body. Angular changes were measured and compared across 3 raters who used 3 different devices (UG, inclinometer, and 2 goniometric apps installed on 3 different smartphones: Apple iPhone 5, LG Android, and Samsung SIII Android). Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to examine interrater reliability and concurrent validity. Results: Interrater reliability for each of the smartphone apps, inclinometer and UG were excellent (ICC = .995–1.000). Concurrent validity was also good (ICC = .998–.999). Based on the Bland-Altman plots, the means of the differences between the devices were low (range = –0.4° to 1.2°). Conclusions: This study identifies the error inherent in measurement that is independent of patient factors and due to the smartphone, the installed apps, and examiner skill. Less than 2° of measurement variability was attributable to those factors alone. The data suggest that 3 smartphones with the 2 installed apps are a viable substitute for using a UG or an inclinometer when measuring angular changes that typically occur when examining ROM and demonstrate the capacity of multiple examiners to accurately use smartphone-based goniometers.

Keywords: goniometer, mobile applications, smartphone, interrater reliability, concurrent validity, psychometric properties

Range of motion (ROM) can be an important compo- nent of the rehabilitation process; its measurement guides the selection of procedural interventions, determines progress during treatment, and identifies appropriate ending points for care.1–5 The universal goniometer (UG) is commonly used in many practice settings, including physical therapy clinics, to examine ROM.6–9 Recently, smartphones equipped with mobile applications (apps) specifically designed to measure ROM have come to offer clinicians a quick and easy method to examine flexibility. At least 15 iOS or Android apps are available for download either for free or for a nominal charge. Some apps directly measure the joint angle while others require the user to take a photo of the joint position before superimposing a virtual goniometer onto it.

With smartphone ownership increasing among clini- cians, there is an increased opportunity to use the devices to support clinical decision making.10 However, with

evolving technology comes the need to assess the utility of the devices for guiding clinical decisions. One must determine if smartphone-based goniometer apps provide a valid measure of ROM and if repeated measurements, both within and between clinicians, are reliable. A number of studies have examined the validity and reliability of smartphone-based goniometer applications designed to measure ROM, taking into account the 3 most common factors that affect measurement—the patient, the device, and the examiner.11 Before using a smartphone device and the installed app on a patient, reliability and validity must be established under standardized conditions.

Any instrument or measurement device used in clinical practice must be valid. The studies examining the validity of smartphones to measure ROM have relied on the iPhone’s built-in inclinometer to assess flexibility.12–14 Tousignant-Laflamme et al,12 using the cervical-ROM device as the gold standard, measured cervical-spine ROM using an iPhone. Concurrent validity, determined using intraclass correlation coefficients (ICCs), was reported to be moderate (ICCs >.50) to good (ICCs >.65) for all motions but poor (ICC <.50) for left rotation. Two other studies looked at 3 different mobile applications using a UG as the gold standard for the comparison. Jones et al15 measured knee flexion using the Simple

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Goniometer App (Ockendon.net) and a UG. Concurrent validity was reported to be high (ICC ≥.93), and there was a positive correlation (r ≥.96) between the 2 devices. Stud- ies by Salamh and Kolber14 and Kolber et al13 assessed standing lumbar lordosis and thoracolumbopelvic flexion, respectively. When comparing the iPhone with a gravity- based bubble inclinometer in asymptomatic participants, both studies reported high concurrent validity, with the ICC equal to .86.

Mitchell et al16 compared 2 mobile apps, Get- MyROM (Interactive Medical Productions LLC) and DrGoniometer (Dr. G, C.D.M. Srl, Milano, Italy), with that of a UG for measures of shoulder external rotation. The ICCs for concurrent validity were reported to range from .93 to .94. In addition, intrarater reliability for the 2 apps ranged from ICC .79 to .81 (UG, ICC = .82), and interrater reliability ranged from .92 to .94 (UG, ICC = .91). The literature suggests that smartphone-based apps have the capacity to be valid when measuring ROM. However, for a measurement instrument to be valid, it must first be reliable.

The studies examining reliability have relied on different types of smartphones (iPhone and Android) and a variety of installed applications.13–15,17–25 Shin et al,17 using a smartphone-based inclinometer to examine active and passive shoulder ROM, reported high inter- rater reliability (ICC >.90) for all motions except internal rotation (ICC <.70). Ockendon and Gilbert18 used an accelerometer-based goniometer in a smartphone for knee flexion and reported the ICC for interrater reliability to be greater than .99, whereas Pollard-McGrandy et al20 found an iPhone goniometry accelerator to be less reli- able for elbow flexion (ICC = .26) and extension (ICC = .06). This was consistent with the work of Eley et al,19 who used the same app to measure knee flexion (ICC = .31) and extension (ICC = .80) and reported moderate to poor interrater reliability. Ferriero et al21 used the iPhone DrGoniometer app to examine elbow ROM and reported good intrarater and interrater reliability (ICC = .99). Of the 3 lower-extremity studies using the DrGoniometer app to examine reliability, Jeon et al23 measured external tibial rotation (ICC = .86), Ferriero et al22 assessed knee motion (ICC all >.95), and Wenzlaff et al24 reported intrarater reliabilities that ranged from .95 to .99 for knee flexion and from .85 to .97 for knee extension. Interrater reliability, while generally high, can be variable based on the joint motion being examined and the type of device and application used. Questions therefore exist regarding the use of apps by multiple raters and the interchange- ability of the devices and apps in measuring flexibility. All of the published studies have focused on examining a single app installed on 1 particular brand of smartphone. There may be differences across applications and types of smartphones that can contribute to measurement vari- ability or error if the devices or applications were to be used interchangeably.

Given the limited number of studies on this emerging technology, it should be noted that all were performed using iPhones. Questions arise about the capacity of

different smartphone devices to measure ROM and their interchangeability in actual clinical practice. None of the current studies examined mobile applications available in the Android market, nor did any studies explore the impact of using the same application on different devices. The purpose of this study was to examine the validity and reliability of 2 goniometric smartphone-based mobile applications. The mobile applications selected for the current study were available for the iOS and Android platforms. This permitted the comparison of the apps with 2 common clinical measures, a UG and an incli- nometer, within each device (iPhone, Android), as well as between clinicians.

Methods

Study Design

This nonexperimental, descriptive study examined the capacity of 3 clinicians to measure 3 different angles using 4 devices intended to measure ROM.

Participants

Three licensed physical therapists with an average of 25 years of experience participated in the study. A fourth investigator (a biomedical engineer) constructed the apparatus and recorded all measurements obtained.

Procedure

Three standardized angles (Figure 1) were constructed to replicate the movement of a hinge joint in the human body. Each standardized angle moved through an arc of motion was limited to a fixed end range of maximal excursion (acute <90°, right ~90°, and obtuse >90°). Using standardized angles eliminates patient factors that can affect repeated measurements and allows the exami- nation of concurrent validity and interrater reliability as both relate to examiner skill and the accuracy of the smartphone devices and the installed apps in determining angular excursion.

Three smartphones were used in this study to measure the ROM of each of the standardized angles: Apple iPhone 5, LG Android, and Samsung Galaxy SIII Android. The reason for selecting the 2 mobile applica- tions used in this study was their availability in both the iOS and Android platforms. Goniometer Records (Indian Orthopedic Research Group, www.iorg.co.in/2013/05/ goniometer-records-mobile-app/) and Goniometer Pro (www.5fuf5.com) were installed on each of the smart- phones. All readings were taken using whole numbers in 1° increments.

A UG (Sammons Preston Standard Goniometer 12.5″ #7514, Patterson Medical, Bolingbrook, IL) and an inclinometer (Johnson Angle Locator #750, Johnson Level & Tool Mfg Co, Mequon, WI) were used. The surfaces of both devices were covered to prevent the examiners from visualizing the readings. The scales on

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the UG (0–360°) and inclinometer (0–180°) provided readings in 1° increments.

The 3 standardized angles were secured to a lev- eled table (Figure 2) after being leveled using wooden shims. In a randomized sequence, 10 measurement trials were performed by each investigator on each of the 3 standardized angles with each device (UG, inclinometer, Apple iPhone 5, LG Android, and Samsung Galaxy SIII Android). Each examiner measured the starting and ending points using the base and arms of each of the standardized angles (Figure 3). The examiner doing the measuring was responsible for aligning the edge of the

smartphone on the standardized angles. After aligning the smartphone, a second investigator was responsible for pushing the buttons that set the starting (0°) and the ending points and reading the measurement. The

Figure 2 — Demonstration of the measurement technique using the smartphone app.

Figure 1 — Angles used for goniometric measurements: (a) Acute angle <90°, (b) right angle ~90°, and (c) obtuse angle >90°.

Figure 3 — Alignment of the smartphone with the lever arm for goniometric measures.

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measurement procedure to identify the available ROM represented by each of the standardized angles was per- formed as described by the application manufacturer. After each measurement, the smartphone reading was cleared and returned to the examiner to take the next measurement. The procedure implemented ensured that the examiner was blinded to the actual reading.

For the UG, the stationary arm was aligned paral- lel to the base of the standardized angle for the starting point of the measurement. The UG axis of rotation was aligned over the center of the hinge joint and the moving arm was aligned to parallel to the angle formed by the arm to identify the maximum excursion allowed. After each measurement, the UG was reset to 0° and returned to the examiner, and the next measurement was taken.

The procedure for measuring available ROM using the inclinometer was performed in a manner similar to the smartphone measurement. The inclinometer (0–180°) was placed on the base of the standardized angle to iden- tify the starting point for the reading. A second reading was taken by placing the inclinometer on the arm of the angle formed by the hinge joint. The difference between the 2 measurements represents the angle of excursion allowed. A second investigator viewed and recorded the readings while the inclinometer was held in place by the examiner. After the reading, the inclinometer was reposi- tioned to a starting point on the base of the standardized angle and the measurement process was repeated.

The investigators using the devices were blinded to all measurements. One investigator (C.N.G.) recorded the readings to ensure that the investigators (R.H.W., D.T.G., and M.L.P.) using the smartphones were blinded. Each investigator performed a total of 240 measurements.

Statistical Analyses

Descriptive statistics (mean and SD) were calculated for each of the smartphones based on the rater taking the measurement, the application installed, and the standard- ized angle being measured. One-way ANOVAs were used to examine differences in how each of the raters used the device and differences between the devices. The first analysis examined differences among the 3 raters based on the type of device used the measure the angles (UG, inclinometer, Apple iPhone 5, LG Android, and Samsung SIII Android). A 1-way ANOVA was also used to determine if measurement differences occurred based solely on the type of device used by all 3 raters compar- ing measurements generated by the UG, the inclinometer, the Apple iPhone 5, the LG Android, and the Samsung SIII Android. For all comparisons, alpha was set at .05.

Concurrent validity and interrater reliability were established using the 2-way mixed ICC for absolute agreement.26,27 Interrater reliability was considered poor for ICC values less than .40, fair for values of .40 to .59, good for values of .60 to .74, and excellent for values of .75 to 1.0.28 The ICC for reliability should be greater than .90 to ensure reasonable validity.27 ICCs and 95% confidence intervals for the ICCs were calculated using

SPSS 17.0 (IBM SPSS, Armonk, NY). Bland-Altman plots were used to further examine agreement and explore the existence of any systematic differences between the measurements.29 MedCalc Version 13.2 (MedCalc Soft- ware, Ostend, Belgium, www.medcalc.org) was used to generate the Bland-Altman plots and identify mean difference, standard deviation of the mean difference, standard error of the mean difference, and the 95% con- fidence interval for the limits of agreement between the Goniometer Record app, Goniometer Pro app, the UG, and the inclinometer. In MedCalc, the Bland-Altman plots represent the results when the same groups of subjects were measured repeatedly, and the true value is constant for each of the measurements taken.

Results Table 1 provides a summary of the ROM measurements based on the type of phone used and the application installed for all of the raters. When examining the means for each of the smartphones, there was some variability in the measurements for the standardized angles. The largest difference between the smartphone measurements based on the installed application was observed when measur- ing the obtuse angle. The ranges of angle differences were 1.57° (<3.4%), 4.96° (<5.5%), and 9.87° (<7.1%) for the acute, right, and obtuse angles, respectively. The maximum excursion of the standardized angles is fixed, and any variability can be assumed to arise from the device or smartphone, the installed application, or the examiners.

Interrater Reliability There were no statistically significant difference between the raters for ROM measured across the 3 standardized angles based on the type of smartphone used and the installed application, the inclinometer, and the UG (F2,87 = 0.001–0.042, P = .981–.999). The ICCs based on mul- tiple raters by type of phone and the installed application were all excellent, ranging from .995 to 1.000 (Table 2). Interrater reliability for the inclinometer (ICC = .995, 95% CI = .985–.998) and UG (ICC = 1.000, 95% CI = .99–1.00) was also excellent.

Concurrent Validity

Table 3 summarizes the ROM measurements for the standardized angles based on the smartphone applica- tion, the UG, and the inclinometer. The means were most similar for the acute and right standardized angles when comparing the apps, the UG, and the inclinometer. The range between the measurements for the obtuse angle when examining the means was 9.87°. Goniometer Pro and the UG had the most similar values for ROM, with the inclinometer and Goniometer Record recording slightly lower values. However, the differences between the applications, the UG, and the inclinometer were not statistically significant (F3,356 = 0.04, P = .99).

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The ICCs for concurrent validity for the 2 smart- phone apps, the inclinometer, and the UG are shown in Table 4. ICCs greater than .90 are considered sufficient to ensure reasonable validity.27 The Bland-Altman plots (Figure 4 and Table 4) provide evidence that the mean

differences based on smartphone application, inclinom- eter, or UG are relatively small (range –0.4° to 1.2°). However, the plots suggest that there is some variability in the pattern of differences based on the angle being measured by the devices (Figure 4).

Table 1 Means, SDs, and Standard Error of the Mean (SEM) for the Goniometer Record, Goniometer Pro, Universal Goniometer, and Inclinometer

Goniometer Record Goniometer Pro

Standardized angle measured

iPhone (n = 30)

LG (n = 30)

Samsung (n = 30)

iPhone (n = 30)

LG (n = 30)

Samsung (n = 30)

Universal goniometer (n = 30)

Inclinometer (n = 30)

Acute <90°

mean 44.73 45.73 46.30 45.00 46.03 44.87 44.97 45.63

SD 0.45 1.23 1.06 0.00 0.49 2.40 0.81 0.93

SEM 0.08 0.22 0.19 0.00 0.09 0.44 0.15 0.17

Right ~90°

mean 88.73 85.77 90.73 88.67 88.33 88.10 89.20 89.57

SD 0.58 1.04 2.78 0.48 0.48 1.03 0.92 0.63

SEM 0.11 0.19 0.51 0.09 0.09 0.19 0.17 0.11

Obtuse> 90°

mean 135.00 133.13 130.80 135.93 134.00 140.67 136.25 134.10

SD 0.00 1.28 1.03 0.25 0.91 1.24 1.13 0.71

SEM 0.00 0.23 0.19 0.05 0.17 0.23 0.21 0.13

Table 2 Interclass Correlation Coefficients (95% Confidence intervals) of Goniometer Mobile Apps Across all Devices

Smartphone

Application iPhone LG Android Samsung SIII Overall

Goniometer Record 1.000 (1.000, 1.000) .997 (.989, .999) .999 (.998, 1.000) .999 (.998, .999)

Goniometer Pro 1.000 (1.000, 1.000) .999 (.999, 1.000) .998 (.992, .999) .999 (.998, .999)

Table 3 Means, SDs, and Standard Error of the Mean (SEM) for the Goniometer Record, Goniometer Pro, Universal Goniometer, and Inclinometer for each of the 3 Angles

Standardized angle measured Goniometer Record

(n = 90) Goniometer Pro

(n = 90) Universal

goniometer (n = 30) Inclinometer

(n = 30)

Acute <90°

mean 45.59 45.30 44.97 45.63

SD 0.59 0.89 0.81 0.93

SEM 0.11 0.16 0.15 0.17

Right ~90°

mean 88.41 88.37 89.20 89.57

SD 1.08 0.58 0.92 0.63

SEM 0.20 0.11 0.17 0.11

Obtuse >90°

mean 132.98 136.87 136.23 134.10

SD 0.36 0.33 1.13 0.71

SEM 0.07 0.06 0.21 0.13

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Discussion Smartphones and installed applications can make mea- suring patient outcomes easier and, as a result, have the potential to change clinical practice. However, when new technologies emerge, it is important to explore the psychometric properties and limitations before using them to make clinical decisions affecting patient care. Several studies have reported on the reliability of mobile apps, but without establishing validity and understanding the sources of measurement variability, reliably wrong measurements have no clinical value.

The current study explored the concurrent validity and interrater reliability of 2 smartphone-based goniom- eter applications. Concurrent validity was established by comparing 2 applications with tools commonly used in everyday clinical practice, the UG and the inclinometer. In routine clinical practice, it is not unusual for more than 1 clinician to be involved in providing direct patient services during an episode of care that spans multiple practice environments. Therefore, the capacity to monitor patient progress over time requires that clinicians have a similar ability to accurately measure the same impair- ment. Thus, the second aim of the study was to examiner interrater reliability. It is important that measures within and between testers produce consistent values.7 Any technology that does not provide reliable outcomes will not be valid for making clinical decisions.

Compared with the previously published literature, the current study took a slightly different approach when examining the validity and reliability of smartphone- based goniometer applications by focusing on 2 of the 3 factors known to affect measurement. The first factor was the variability arising from the examiners’ skill in using each of the devices to measure a known angle. The second source of variability was inherent to the capacity of the smartphones and the installed applications to quantify angular differences by identifying changes in orientation using the internally embedded microelectromechanical accelerometers, magnetometers, and gyroscopes. The third factor, not considered in the study, is the influence of patient-specific factors that contribute to measurement variability. In this study, using standardized angles whose

maximum excursions were known eliminated this last factor and provides a perspective on how much error is due to the type of phone, installed application, and examiner skill. When attempting to minimize measure- ment error and make sound clinical judgments, knowing the source of the variability helps improve objectivity. Rater or user training can be more effectively targeted to minimize error.

To date, no other research studies have examined the capacity of apps installed on Android devices to accurately measure ROM. The current study is the first known to examine goniometric applications installed on different smartphones. When considering examiner skill and the capacity of the instruments to measure ROM, interrater reliability was excellent based on the ICCs found (Table 2). The current study examined interrater reliability between the individual examiners using the goniometer apps installed on 3 different smartphones, the inclinometer, and the UG. However, the difference among the means based on the smartphone used and the installed application suggests the potential for clinically meaningful differences to arise when measuring angles greater than 90°. For example, a 10° difference between the Goniometer Record app and the Goniometer Pro app was found when the Samsung Galaxy SIII was used to measure the obtuse standardized angle. When installed on either the iPhone or LG, the 2 apps yielded outcomes that were more similar. This finding was less of an issue for the acute and right standardized angles. Differences in how each of the phones record angular positions may be a factor. In addition, the Samsung Galaxy SIII, when embedded in a case, has a more rounded edge that allows some variability in the measurement when placed on a flat surface. Of the 3 smartphones, the iPhone has a flat edge that permits easier alignment to the surface of the standardized angles. However, based on the data, different raters using the same phone produced consistent, highly reliable results. Differences may only arise when differ- ent combinations of phones and apps are used to measure ROM. This is an area that requires greater exploration given the current status of the literature.

The current study used mobile apps available in both markets and on 3 different smartphones. To identify

Table 4 Statistical Summary of the Comparison of All the Goniometric Measurement Devices

ICC (95% CI) MD SEMD (95% CI) SDMD 95% CI LoA

Goniometer Record, inclinometer .999 (.998, 1.000) 0.8 0.1 (0.5, 1 .0) 1.2 –1.4 to 3.0

Goniometer Pro, inclinometer .998 (.998, .999) –0.4 0.2 (–0.8, 0.1) 2.0 –4.4 to 3.6

Goniometer Record, universal goniometer .998 (.995, .999) 1.1 0.2 (0.7, 1.6) 2.0 –2.9 to 5.2

Goniometer Pro, universal goniometer .999 (.999, 1.000) –0.04 0.1 (–0.3, 0.3) 1.3 –2.5 to 2.5

Goniometer Pro, goniometer record .998 (.995, .999) 1.2 0.2 (–1.6, –0.8) 2.0 –5.2 to 2.9

Inclinometer, universal goniometer .999 (.998, .999) –0.4 0.2 (–0.7, 0.0) 1.8 –3.8 to 3.5

Abbreviations: ICC, intraclass correlation coefficient; MD, mean of differences; SDMD, SD of MD; SEMD, standard error of MD; CI LoA: 95% confidence interval of the limits of agreement.

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Figure 4 — Bland-Altman plots for comparison of smartphone apps, universal goniometer, and inclinometer.

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concurrent validity, the Goniometer Pro and Goni- ometer Record apps were compared with the UG and inclinometer. ICC values ranged from .996 to .999 and Bland-Altman plots revealed mean differences among the devices that ranged from –0.4° to 1.2°. The 95% confidence interval for the limits of agreement may be acceptable when making clinical decisions if one were to use the apps interchangeably. This suggests that the apps installed on the smartphones have the capacity to act as a substitute for a UG or inclinometer. Current evidence using a UG has found goniometric measures of several joints to be valid. Gogia et al30 reported goniometric knee-measurement validity to be .97 to .98. Kolber and Hanney31 reported goniometric validity of various shoulder measurements to be ≥.85. Converted into degrees of motion, validity studies of goniometric measures have deemed a maximal error of 10° or less to be clinically acceptable.32 Thus, both mobile apps used on the Apple and Android devices fared well against devices that are commonly used in clinical practice. With smartphones becoming more common, the data from the current study suggest that the Goniometer Pro and Goniometer Record mobile applications may be viable substitutes for using a UG or an inclinometer when measuring ROM. Multiple physical therapists can use the same application or device to arrive at a similar measurement.

Conclusions The current study provides insight into the capacity of multiple examiners to accurately use smartphone-based goniometers, as well as the precision of the various smartphones. The data suggest that multiple raters can use each of the smartphones with the installed apps, the UG, and inclinometer in a manner that generates reliable measurements. Smartphone-based apps can be used in place of the UG and inclinometers, and any differences may not be clinically meaningful. The current study adds to literature by examining how different smartphones measure ROM based on the manufacturer (Apple, LG, or Samsung), operating system (iOS or Android) and installed app (Goniometer Record or Goniometer Pro). The use of standardized angles removed the influence of patient factors affecting the measurement.

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