Authors: Sophie Louise Vohralik, BAppSc (Physiotherapy)(Hons) Annika Rose Bowen, BAppSc (Physiotherapy)(Hons) Joshua Burns, BAppSc (Podiatry)(Hons), PhD Claire Elizabeth Hiller, BAppSc (Physiotherapy), MAppSc, PhD Elizabeth Jean Nightingale, BAppSc (Physiotherapy), MBiomedE, PhD
Measurement
BRIEF REPORT
Affiliations: From the Arthritis and Musculoskeletal Research Group, Faculty of Health Sciences, The University of Sydney, Cumberland Campus, Lidcombe (SLV, ARB, JB, CEH, EJN); and Paediatric Gait Analysis Service of New South Wales, The Children’s Hospital at Westmead, Westmead, Australia (JB).
Correspondence:
Disclosures: Sophie Louise Vohralik, BAppSc(Physiotherapy)(Hons), and Annika Rose Bowen, BAppSc(Physiotherapy)(Hons), are joint first authors. Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.
DOI: 10.1097/PHM.0000000000000221
www.ajpmr.com
ABSTRACT Vohralik SL, Bowen AR, Burns J, Hiller CE, Nightingale EJ: Reliability and validity of a smartphone app to measure joint range. Am J Phys Med Rehabil 2015;94:325Y330.
All correspondence and requests for reprints should be addressed to: Elizabeth Jean Nightingale, BAppSc(Physiotherapy), MBiomedE, PhD, Faculty of Health Sciences, University of Sydney, 75 East St, Lidcombe, New South Wales 2141, Australia.
0894-9115/15/9404-0325 American Journal of Physical Medicine & Rehabilitation Copyright * 2014 Wolters Kluwer Health, Inc. All rights reserved.
Reliability and Validity of a Smartphone App to Measure Joint Range
In clinical and research settings, objective range of motion measurement is an essential component of lower limb assessment and treatment evaluation. One reliable tool is the digital inclinometer; however, availability and cost preclude its widespread use. Smartphone apps are now widely available, allowing smartphones to be used as an inclinometer. Reliability and validity studies of new technologies are scarce. Intrarater and interrater reliability of the iHandy Level app installed on a smartphone and an inclinometer were assessed in 20 participants for ankle dorsiflexion using a weight-bearing lunge test. Criterion validity was assessed between a Fastrak and the app, and construct validity was assessed between the inclinometer and the app. Intraclass correlation coefficients2,1 demonstrated excellent intrarater and interrater reliability (intraclass correlation coefficient, 0.97 and 0.76, respectively). Tests of validity demonstrated excellent correlation between all three methods (r 2 9 0.99). The smartphone app is both reliable and valid, provides a low-cost method of measuring range of motion, and can be easily incorporated into clinical practice. Key Words: Range of Motion, Ankle Joint, Measurement Accuracy, Biomedical Technology, Cellular Phone
BACKGROUND Accurate measurement of joint range of motion is often required in biomechanical research and clinical practice. One of the most reliable tools to measure joint range is the digital inclinometer1,2; however, accessibility and cost often preclude its use. Several methods have been reported in the literature for measuring joint range, such as video-based three-dimensional kinematics,3 Fastrak,4,5 goniometers,2,3,6Y8 and digital inclinometers.2,3,7,9 Considering just ankle dorsiflexion range, only the reliability of digital inclinometer measurements has been considered to date.1Y3,7,9 The validity of digital inclinometer measurements is really considered only in cervical spine and shoulder measurement, in which the large range of motion across multiple planes can alter the values obtained considerably.10,11 With the advent of the smartphone, there are now many free applications (apps) available (e.g., the TiltMeter, Clinometer, and A Smartphone App to Measure Joint Range Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
325
Inclinometer) allowing the smartphone to be used as an inclinometer. An inclinometer is popular because it is easy to use and requires just one standardized point for testing compared with a goniometer or more complex biomechanical instruments such as the Fastrak. The inclinometer (approximately $620), despite its relative cost savings compared with biomechanical instruments (9$5000), is often still regarded as too expensive for the clinical setting. Therefore, cost or impracticalities preclude many of these devices being used routinely. The aim of this study was to evaluate the reliability and validity of a free smartphone inclinometer app, the iHandy Level, for ankle dorsiflexion, using a weight-bearing lunge test.
METHODS Reliability With the use of a sample of convenience, ankle dorsiflexion range of motion was assessed in 20 healthy participants (7 men and 13 women), aged 21Y28 yrs (mean [SD], 22.4 [2] yrs), with a mean (SD) height of 172.5 (8.9) and a mean (SD) weight of 67.2 (12.9). The participants were active university students with no history of lower limb injury in the past year. The study was approved by The University of Sydney, Human Research Ethics committee, and the participants gave their written consent before participation. Ankle dorsiflexion range was measured using a digital, medically rated inclinometer (Baseline; Fabrication Enterprises Incorporated, New York; Fig. 1A)
and the iHandy Level app on an iPhone (iPhone; Apple, Cupertino, CA; Fig. 1B). The participants were assessed independently by two raters on one occasion. The raters were physiotherapy honor students in their final year of study. One student performed the measures, whereas the other recorded the measures to maintain blinding. Both students assessed the participant initially for interrater reliability, with reassessment occurring after a rest period of 5 mins for intrarater reliability. Before testing, each participant actively performed three 30-sec calf stretches on their right leg to warm up. The test procedure was explained and demonstrated to each participant. On the basis of the published lunge test method, testing involved each assessor marking a point 15 cm distal to the tibial tuberosity on the anterior border of the tibia with a felt-tipped pen.1 Between each test, the mark was removed with an alcohol wipe. This was the placement point for each device, and the order of the devices was randomized. To standardize device placement, the BHome[ button on the short side of the iPhone and BB[ from the word baseline for the inclinometer were aligned with the mark on the tibia. To ensure the same foot placement for testing, the distance of the great toe from the wall was measured, recorded, and reused for each test (Figs. 1A, B). The participants’ right foot was positioned perpendicular to a wall, using their hands in front of them for balance.1 A tape measure was placed on the floor to ensure that the second toe and the center of their heel were aligned perpendicular to the wall,
FIGURE 1 Measurement devices used: baseline inclinometer (A) and iPhone with iHandy Level app (B).
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Vohralik et al.
Am. J. Phys. Med. Rehabil. & Vol. 94, No. 4, April 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
TABLE 1 Intrarater reliability
Inclinometer Smartphone app
Difference Between Mean Angles, Degrees
SEM
ICC2,1
95% CI (Lower Bound)
95% CI (Upper Bound)
0.07 0.20
1.25 1.35
0.98 0.97
0.95 0.92
0.99 0.99
and the participants were instructed to lunge forward, bringing their knee in contact with a vertical tape on the wall. For the first test, the participants were encouraged to keep moving their foot away from the wall to obtain the largest angle possible, while keeping their heel on the ground. For each device, three measurements were obtained to calculate a mean angle.
Validity Criterion validity was tested using 20 pieces of timber with angles ranging between 0 and 58 degrees. This was done to control the number of variables that could potentially contribute to differences in angular readings that may be affected by soft tissue viscosity.12 One Fastrak sensor was used, and angular data were collected by custom-made LabVIEW software. The Fastrak data were used as the criterion standard measure.13,14 Angles were measured using a 3Space Fastrak (Polhemius, Inc, Vermont), the app, and the digital inclinometer, in that order. Each piece of timber had a dot in the middle of the bottom edge and was marked with the angle in which it was cut. The angle measure was covered by a piece of paper, and the assessor measuring the angle remained blinded to the angles of the pieces of timber. Each device was lined up with the dot on the timber to obtain a measure. Three measurements were obtained with each device for all 20 pieces of timber, and a mean measure was then calculated for each device.
Statistics SPSS (IBM SPSS Statistics for Windows, version 21.0; IBM Corp, Armonk, NY) was used to calculate intraclass correlation coefficients (ICCs2,1) and 95% confidence intervals (CIs) to determine intrarater and interrater reliability. ICCs were interpreted according to Fleiss,15 whereby coefficients of less than 0.4 were considered poor, coefficients between 0.4 and 0.75 were fair/good, and coefficients greater than 0.75 were excellent. Standard error of the measure and Bland-Altman plots were also produced. Pearson product-moment correlation coefficients were calculated to assess the criterion validity between the smartphone app and the Fastrak (criterion standard) as well as the construct validity between the iPhone app and the digital inclinometer.
RESULTS Reliability Intrarater Reliability The ICCs and 95% CIs for the inclinometer and the smartphone app were both in the excellent range (0.98; CI, 0.95Y0.99, and 0.97; CI, 0.92Y0.99, respectively), with narrow CIs. There was only a 0.07-degree and 0.2-degree difference between sessions for the inclinometer and the app, respectively (Table 1). Standard error of the measure (Table 1) and Bland-Altman plots (Fig. 2) demonstrate that the inclinometer measures were closer together,
FIGURE 2 Bland-Altman plots of intrarater reliability with mean (solid line) and 2 SDs (dashed lines) marked. A, Inclinometer; B, iPhone. www.ajpmr.com
A Smartphone App to Measure Joint Range Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
327
TABLE 2 Interrater reliability Difference Between Mean Angles, Degrees
SEM
ICC2,1
95% CI (Lower Bound)
95% CI (Upper Bound)
2.00 3.40
2.05 2.68
0.90 0.76
0.43 0.01
0.97 0.93
Inclinometer Smartphone app
with the mean differences smaller than those of the smartphone app, although the differences are not significant.
Interrater Reliability The ICCs for the inclinometer and the smartphone app were both in the excellent range (0.90; CI, 0.43Y0.97, and 0.76; CI, 0.005Y0.932, respectively), although CIs were wider (Table 2). There was a 2-degree difference between assessors with the inclinometer and a 3.4-degree difference with the smartphone app. Standard error of the measure (Table 2) and Bland-Altman plots (Fig. 3) demonstrate the same trend as the intrarater reliability, with larger differences as is typical in clinical measures, whereby intrarater reliability is better than interrater reliability.
Validity The iHandy Level was highly correlated with both the Fastrak (r 2 = 0.99, P G 0.01) and the digital inclinometer (r2 = 1.0, P G 0.01). The smartphone predicted 99.9% of the variation of the inclinometer and 99.8% of the variation of the Fastrak when measuring static angles (Fig. 4).
DISCUSSION The iHandy Level app is a reliable and valid measure of ankle dorsiflexion range of motion. The
results of this study concur with the high reliability of the TiltMeter app,16 the only other app validated for the ankle to date.17 The iHandy Level is designed to use the inbuilt accelerometers of the smartphone, and since this study was conducted, it has been validated for measuring spine mobility, although its development was initially for use in carpentry.18 The TiltMeter app in comparison is a magnetometer-based app and, although reliable in measuring ankle dorsiflexion, is limited to measures in the horizontal plane. The use of apps in joint measurement is a growing area as demonstrated by the first systematic review in this area that collected 17 articles from 2011 onward.17 Many of the available apps use the inbuilt accelerometers of the smartphone, but magnetometers and photographic systems are also used. The apps make an attractive alternative to other clinical methods because of their cheapness and availability across a range of smartphones and, in comparison with goniometry, their ease and speed of use. Hygiene issues are similar to those encountered using an inclinometer, and smartphones with smoother exteriors that may be wiped down with alcohol wipes do have advantages for this aspect in clinical practice and research use. Both intrarater and interrater reliabilities of this study were excellent, with greater intrarater reliability, as is typical of clinical measures. Lower interrater reliability might be explained by the size
FIGURE 3 Bland-Altman plots of interrater reliability with mean (solid line) and 2 SDs (dashed lines) marked. A, Inclinometer; B, iPhone.
328
Vohralik et al.
Am. J. Phys. Med. Rehabil. & Vol. 94, No. 4, April 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
FIGURE 4 Bland-Altman plots of validity with mean (solid line) and 2 SDs (dashed lines) marked. A, iPhone vs. Fastrak; B, inclinometer vs. Fastrak.
difference between the inclinometer compared with the smartphone app. The smartphone has a narrower base, making it more difficult to place consistently on the patient across multiple planes, possibly introducing more error in the measurements. In this study, the short side of the smartphone was used, making it less stable, and, in the future, the authors recommend that the long side be used to try and minimize placement variation between raters. High levels of construct and criterion validity have been demonstrated, with r 2 values of 0.99 and 1.0 for the Fastrak and the inclinometer, respectively. Comparison of the smartphone app with the Fastrak as the criterion standard angular measurement tool was almost perfect. Further research should determine whether these high levels of validity transfer directly to the measurement of all joint angles. Blinding of assessors was one of the study strengths but did cause difficulties not usually encountered in clinical practice. To achieve blinding in the reliability study, the devices were faced away from the assessor. Maintaining the device position without clearly visualizing the display was difficult. Future studies could mark a spot on the back of each device to ensure that the correct position was maintained and use the long edge of the smartphone to maximize accurate placement. Possible limitations of this study include a sample of convenience for reliability testing. The participants were predominantly young and healthy, with little limitation to ankle dorsiflexion. Therefore, these results may not generalize across a wider population with greater range of motion. Validation with human participants would also confirm the generalizability of the iHandy Level app. In conclusion, a smartphone with the iHandy app can be used in clinical practice and research as an easy and convenient alternative to an inclinometer. A smartphone with the iHandy Level app can www.ajpmr.com
measure ankle dorsiflexion with high reliability as well as construct and criterion validity. REFERENCES 1. Bennell KL, Talbot RC, Wajswelner H, et al: Intra-rater and inter-rater reliability of a weight-bearing lunge measure of ankle dorsiflexion. Aust J Physiother 1998; 44:175Y80 2. Konor MM, Morton S, Eckerson JM, et al: Reliability of three measures of ankle dorsiflexion range of motion. Int J Sports Phys Ther 2012;7:279Y87 3. Sidaway B, Euloth T, Caron H, et al: Comparing the reliability of a trigonometric technique to goniometry and inclinometry in measuring ankle dorsiflexion. Gait Posture 2012;36:335Y9 4. Menadue C, Raymond J, Kilbreath SL, et al: Reliability of two goniometric methods of measuring active inversion and eversion range of motion at the ankle. BMC Musculoskelet Disord 2006;7:60 5. Morphett AL, Crawford CM, Lee D: The use of electromagnetic tracking technology for measurement of passive cervical range of motion: A pilot study. J Manipulative Physiol Ther 2003;26:152Y9 6. Ekstrand J, Wiktorsson M, Oberg B, et al: Lower extremity goniometric measurements: A study to determine their reliability. Arch Phys Med Rehabil 1982; 63:171Y5 7. Gatt A, Chockalingam N: Clinical assessment of ankle joint dorsiflexion: a review of measurement techniques. J Am Podiatr Med Assoc 2011;101:59Y69 8. Kim PJ, Peace R, Mieras J, et al: Interrater and intrarater reliability in the measurement of ankle joint dorsiflexion is independent of examiner experience and technique used. J Am Podiatr Med Assoc 2011;101: 407Y14 9. Munteanu SE, Strawhorn AB, Landorf KB, et al: A weightbearing technique for the measurement of ankle joint dorsiflexion with the knee extended is reliable. J Sci Med Sport 2009;12:54Y9 10. Kolber MJ, Hanney WJ: The reliability and concurrent validity of shoulder mobility measurements using a
A Smartphone App to Measure Joint Range Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
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digital inclinometer and goniometer: A technical report. Int J Sports Phys Ther 2012;7:306Y13
15. Fleiss J: The Design and Analysis of Clinical Experiments. New York: John Wiley & Sons, 1986
11. Prushansky T, Deryi O, Jabarreen B: Reproducibility and validity of digital inclinometry for measuring cervical range of motion in normal subjects. Physiother Res Int 2010;15:42Y8
16. Williams CM, Caserta AJ, Haines TP: The TiltMeter app is a novel and accurate measurement tool for the weight bearing lunge test. J Sci Med Sport 2013;5:392Y5
12. Taylor DC, Dalton JD Jr, Seaber AV, et al: Viscoelastic properties of muscle-tendon units. The biomechanical effects of stretching. Am J Sports Med 1990;18:300Y9
17. Milani P, Coccetta CA, Rabini A, et al: Mobile smartphone applications for body position measurement in rehabilitation: A review of goniometric tools. PM R 2014;pii:S1934Y482
13. Mannion A, Troke M: A comparison of two motion analysis devices used in the measurement of lumbar spinal mobility. Clin Biomech (Bristol, Avon) 1999;14:612Y9 14. Pearcy MJ, Hindle RJ: New method for the non-invasive three-dimensional measurement of human back movement. Clin Biomech (Bristol, Avon) 1989;4:73Y9
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18. Salamh PA, Kolber M: The reliability, minimal detectable change and concurrent validity of a gravity-based bubble inclinometer and iPhone application for measuring standing lumbar lordosis. Physiother Theory Pract 2014;30:62Y7
Am. J. Phys. Med. Rehabil. & Vol. 94, No. 4, April 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Measurement
BRIEF REPORT
Affiliations: From the Arthritis and Musculoskeletal Research Group, Faculty of Health Sciences, The University of Sydney, Cumberland Campus, Lidcombe (SLV, ARB, JB, CEH, EJN); and Paediatric Gait Analysis Service of New South Wales, The Children’s Hospital at Westmead, Westmead, Australia (JB).
Correspondence:
Disclosures: Sophie Louise Vohralik, BAppSc(Physiotherapy)(Hons), and Annika Rose Bowen, BAppSc(Physiotherapy)(Hons), are joint first authors. Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.
DOI: 10.1097/PHM.0000000000000221
www.ajpmr.com
ABSTRACT Vohralik SL, Bowen AR, Burns J, Hiller CE, Nightingale EJ: Reliability and validity of a smartphone app to measure joint range. Am J Phys Med Rehabil 2015;94:325Y330.
All correspondence and requests for reprints should be addressed to: Elizabeth Jean Nightingale, BAppSc(Physiotherapy), MBiomedE, PhD, Faculty of Health Sciences, University of Sydney, 75 East St, Lidcombe, New South Wales 2141, Australia.
0894-9115/15/9404-0325 American Journal of Physical Medicine & Rehabilitation Copyright * 2014 Wolters Kluwer Health, Inc. All rights reserved.
Reliability and Validity of a Smartphone App to Measure Joint Range
In clinical and research settings, objective range of motion measurement is an essential component of lower limb assessment and treatment evaluation. One reliable tool is the digital inclinometer; however, availability and cost preclude its widespread use. Smartphone apps are now widely available, allowing smartphones to be used as an inclinometer. Reliability and validity studies of new technologies are scarce. Intrarater and interrater reliability of the iHandy Level app installed on a smartphone and an inclinometer were assessed in 20 participants for ankle dorsiflexion using a weight-bearing lunge test. Criterion validity was assessed between a Fastrak and the app, and construct validity was assessed between the inclinometer and the app. Intraclass correlation coefficients2,1 demonstrated excellent intrarater and interrater reliability (intraclass correlation coefficient, 0.97 and 0.76, respectively). Tests of validity demonstrated excellent correlation between all three methods (r 2 9 0.99). The smartphone app is both reliable and valid, provides a low-cost method of measuring range of motion, and can be easily incorporated into clinical practice. Key Words: Range of Motion, Ankle Joint, Measurement Accuracy, Biomedical Technology, Cellular Phone
BACKGROUND Accurate measurement of joint range of motion is often required in biomechanical research and clinical practice. One of the most reliable tools to measure joint range is the digital inclinometer1,2; however, accessibility and cost often preclude its use. Several methods have been reported in the literature for measuring joint range, such as video-based three-dimensional kinematics,3 Fastrak,4,5 goniometers,2,3,6Y8 and digital inclinometers.2,3,7,9 Considering just ankle dorsiflexion range, only the reliability of digital inclinometer measurements has been considered to date.1Y3,7,9 The validity of digital inclinometer measurements is really considered only in cervical spine and shoulder measurement, in which the large range of motion across multiple planes can alter the values obtained considerably.10,11 With the advent of the smartphone, there are now many free applications (apps) available (e.g., the TiltMeter, Clinometer, and A Smartphone App to Measure Joint Range Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
325
Inclinometer) allowing the smartphone to be used as an inclinometer. An inclinometer is popular because it is easy to use and requires just one standardized point for testing compared with a goniometer or more complex biomechanical instruments such as the Fastrak. The inclinometer (approximately $620), despite its relative cost savings compared with biomechanical instruments (9$5000), is often still regarded as too expensive for the clinical setting. Therefore, cost or impracticalities preclude many of these devices being used routinely. The aim of this study was to evaluate the reliability and validity of a free smartphone inclinometer app, the iHandy Level, for ankle dorsiflexion, using a weight-bearing lunge test.
METHODS Reliability With the use of a sample of convenience, ankle dorsiflexion range of motion was assessed in 20 healthy participants (7 men and 13 women), aged 21Y28 yrs (mean [SD], 22.4 [2] yrs), with a mean (SD) height of 172.5 (8.9) and a mean (SD) weight of 67.2 (12.9). The participants were active university students with no history of lower limb injury in the past year. The study was approved by The University of Sydney, Human Research Ethics committee, and the participants gave their written consent before participation. Ankle dorsiflexion range was measured using a digital, medically rated inclinometer (Baseline; Fabrication Enterprises Incorporated, New York; Fig. 1A)
and the iHandy Level app on an iPhone (iPhone; Apple, Cupertino, CA; Fig. 1B). The participants were assessed independently by two raters on one occasion. The raters were physiotherapy honor students in their final year of study. One student performed the measures, whereas the other recorded the measures to maintain blinding. Both students assessed the participant initially for interrater reliability, with reassessment occurring after a rest period of 5 mins for intrarater reliability. Before testing, each participant actively performed three 30-sec calf stretches on their right leg to warm up. The test procedure was explained and demonstrated to each participant. On the basis of the published lunge test method, testing involved each assessor marking a point 15 cm distal to the tibial tuberosity on the anterior border of the tibia with a felt-tipped pen.1 Between each test, the mark was removed with an alcohol wipe. This was the placement point for each device, and the order of the devices was randomized. To standardize device placement, the BHome[ button on the short side of the iPhone and BB[ from the word baseline for the inclinometer were aligned with the mark on the tibia. To ensure the same foot placement for testing, the distance of the great toe from the wall was measured, recorded, and reused for each test (Figs. 1A, B). The participants’ right foot was positioned perpendicular to a wall, using their hands in front of them for balance.1 A tape measure was placed on the floor to ensure that the second toe and the center of their heel were aligned perpendicular to the wall,
FIGURE 1 Measurement devices used: baseline inclinometer (A) and iPhone with iHandy Level app (B).
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Vohralik et al.
Am. J. Phys. Med. Rehabil. & Vol. 94, No. 4, April 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
TABLE 1 Intrarater reliability
Inclinometer Smartphone app
Difference Between Mean Angles, Degrees
SEM
ICC2,1
95% CI (Lower Bound)
95% CI (Upper Bound)
0.07 0.20
1.25 1.35
0.98 0.97
0.95 0.92
0.99 0.99
and the participants were instructed to lunge forward, bringing their knee in contact with a vertical tape on the wall. For the first test, the participants were encouraged to keep moving their foot away from the wall to obtain the largest angle possible, while keeping their heel on the ground. For each device, three measurements were obtained to calculate a mean angle.
Validity Criterion validity was tested using 20 pieces of timber with angles ranging between 0 and 58 degrees. This was done to control the number of variables that could potentially contribute to differences in angular readings that may be affected by soft tissue viscosity.12 One Fastrak sensor was used, and angular data were collected by custom-made LabVIEW software. The Fastrak data were used as the criterion standard measure.13,14 Angles were measured using a 3Space Fastrak (Polhemius, Inc, Vermont), the app, and the digital inclinometer, in that order. Each piece of timber had a dot in the middle of the bottom edge and was marked with the angle in which it was cut. The angle measure was covered by a piece of paper, and the assessor measuring the angle remained blinded to the angles of the pieces of timber. Each device was lined up with the dot on the timber to obtain a measure. Three measurements were obtained with each device for all 20 pieces of timber, and a mean measure was then calculated for each device.
Statistics SPSS (IBM SPSS Statistics for Windows, version 21.0; IBM Corp, Armonk, NY) was used to calculate intraclass correlation coefficients (ICCs2,1) and 95% confidence intervals (CIs) to determine intrarater and interrater reliability. ICCs were interpreted according to Fleiss,15 whereby coefficients of less than 0.4 were considered poor, coefficients between 0.4 and 0.75 were fair/good, and coefficients greater than 0.75 were excellent. Standard error of the measure and Bland-Altman plots were also produced. Pearson product-moment correlation coefficients were calculated to assess the criterion validity between the smartphone app and the Fastrak (criterion standard) as well as the construct validity between the iPhone app and the digital inclinometer.
RESULTS Reliability Intrarater Reliability The ICCs and 95% CIs for the inclinometer and the smartphone app were both in the excellent range (0.98; CI, 0.95Y0.99, and 0.97; CI, 0.92Y0.99, respectively), with narrow CIs. There was only a 0.07-degree and 0.2-degree difference between sessions for the inclinometer and the app, respectively (Table 1). Standard error of the measure (Table 1) and Bland-Altman plots (Fig. 2) demonstrate that the inclinometer measures were closer together,
FIGURE 2 Bland-Altman plots of intrarater reliability with mean (solid line) and 2 SDs (dashed lines) marked. A, Inclinometer; B, iPhone. www.ajpmr.com
A Smartphone App to Measure Joint Range Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
327
TABLE 2 Interrater reliability Difference Between Mean Angles, Degrees
SEM
ICC2,1
95% CI (Lower Bound)
95% CI (Upper Bound)
2.00 3.40
2.05 2.68
0.90 0.76
0.43 0.01
0.97 0.93
Inclinometer Smartphone app
with the mean differences smaller than those of the smartphone app, although the differences are not significant.
Interrater Reliability The ICCs for the inclinometer and the smartphone app were both in the excellent range (0.90; CI, 0.43Y0.97, and 0.76; CI, 0.005Y0.932, respectively), although CIs were wider (Table 2). There was a 2-degree difference between assessors with the inclinometer and a 3.4-degree difference with the smartphone app. Standard error of the measure (Table 2) and Bland-Altman plots (Fig. 3) demonstrate the same trend as the intrarater reliability, with larger differences as is typical in clinical measures, whereby intrarater reliability is better than interrater reliability.
Validity The iHandy Level was highly correlated with both the Fastrak (r 2 = 0.99, P G 0.01) and the digital inclinometer (r2 = 1.0, P G 0.01). The smartphone predicted 99.9% of the variation of the inclinometer and 99.8% of the variation of the Fastrak when measuring static angles (Fig. 4).
DISCUSSION The iHandy Level app is a reliable and valid measure of ankle dorsiflexion range of motion. The
results of this study concur with the high reliability of the TiltMeter app,16 the only other app validated for the ankle to date.17 The iHandy Level is designed to use the inbuilt accelerometers of the smartphone, and since this study was conducted, it has been validated for measuring spine mobility, although its development was initially for use in carpentry.18 The TiltMeter app in comparison is a magnetometer-based app and, although reliable in measuring ankle dorsiflexion, is limited to measures in the horizontal plane. The use of apps in joint measurement is a growing area as demonstrated by the first systematic review in this area that collected 17 articles from 2011 onward.17 Many of the available apps use the inbuilt accelerometers of the smartphone, but magnetometers and photographic systems are also used. The apps make an attractive alternative to other clinical methods because of their cheapness and availability across a range of smartphones and, in comparison with goniometry, their ease and speed of use. Hygiene issues are similar to those encountered using an inclinometer, and smartphones with smoother exteriors that may be wiped down with alcohol wipes do have advantages for this aspect in clinical practice and research use. Both intrarater and interrater reliabilities of this study were excellent, with greater intrarater reliability, as is typical of clinical measures. Lower interrater reliability might be explained by the size
FIGURE 3 Bland-Altman plots of interrater reliability with mean (solid line) and 2 SDs (dashed lines) marked. A, Inclinometer; B, iPhone.
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Vohralik et al.
Am. J. Phys. Med. Rehabil. & Vol. 94, No. 4, April 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
FIGURE 4 Bland-Altman plots of validity with mean (solid line) and 2 SDs (dashed lines) marked. A, iPhone vs. Fastrak; B, inclinometer vs. Fastrak.
difference between the inclinometer compared with the smartphone app. The smartphone has a narrower base, making it more difficult to place consistently on the patient across multiple planes, possibly introducing more error in the measurements. In this study, the short side of the smartphone was used, making it less stable, and, in the future, the authors recommend that the long side be used to try and minimize placement variation between raters. High levels of construct and criterion validity have been demonstrated, with r 2 values of 0.99 and 1.0 for the Fastrak and the inclinometer, respectively. Comparison of the smartphone app with the Fastrak as the criterion standard angular measurement tool was almost perfect. Further research should determine whether these high levels of validity transfer directly to the measurement of all joint angles. Blinding of assessors was one of the study strengths but did cause difficulties not usually encountered in clinical practice. To achieve blinding in the reliability study, the devices were faced away from the assessor. Maintaining the device position without clearly visualizing the display was difficult. Future studies could mark a spot on the back of each device to ensure that the correct position was maintained and use the long edge of the smartphone to maximize accurate placement. Possible limitations of this study include a sample of convenience for reliability testing. The participants were predominantly young and healthy, with little limitation to ankle dorsiflexion. Therefore, these results may not generalize across a wider population with greater range of motion. Validation with human participants would also confirm the generalizability of the iHandy Level app. In conclusion, a smartphone with the iHandy app can be used in clinical practice and research as an easy and convenient alternative to an inclinometer. A smartphone with the iHandy Level app can www.ajpmr.com
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