Validity and reliability of a smartphone goniometer application for measuring hip range of motions

Abstract

BACKGROUND:

Mobile applications which are designed to assess the range of motion (ROM) are widely used.

OBJECTIVE:

The aim of this cross-sectional observational study was to determine the inter-observer and intra-observer reliability of a smartphone application “PT Goniometer” (PTG) and determine the correlation between PTG and universal goniometer (UG) regarding active ROMs of the hip in healthy participants.

METHODS:

Thirty-four healthy young participants were included in the study. Two physiotherapists performed active hip flexion, abduction, internal rotation and external rotation ROM measurements of dominant legs of the participants by using PTG and UG. Intraclass correlation coefficients (ICC) were calculated to determine the intra-observer and inter-observer reliability. Level of correlations between PTG and UG were used to establish concurrent validity of PTG.

RESULTS:

The PTG demonstrated excellent inter-observer and intra-observer reliability (ICC > 0.90) for all measured hip movements. The minimum detectable change (MDC₉₅) was ranged from 3.29° to 5.1° for the intra-observer reliability, and from 2.55° to 3.21° for the inter-observer reliability. Additionally, the concurrent validity was found excellent (r = 0.91–0.93).

CONCLUSION:

The results of the present study suggest that PTG is a valid and reliable mobile technology for measuring hip ROMs.

Keywords

Hip joint range of motion technology assessment mobile applications

1 Introduction

Measuring range of motion (ROM) is an essential part of a comprehensive examination of the movement ability of joints and surrounding soft tissue. ROM examination is generally performed to screen a possible impairment, to establish a diagnosis, to determine the prognosis, to evaluate the rehabilitative goals, to modify the treatment, to motivate the patient, to investigate the effectiveness of therapeutic approaches, and to decide for adaptive equipment such as orthoses and braces [1, 2].

Many measurement tools are available for determining the ROM such as universal goniometers (UG), visual estimation method, bubble inclinometers, digital inclinometers, motion analyses systems, and mobile technologies. UG based assessment of the hip extension ROM have demonstrated high inter-observer (ICC = 0.89–0.92) and intra-observer (ICC = 0.91–0.93) reliability in healthy population [3]. Besides, Gradoz et al. found that UG have good inter/intra-rater reliability for determining passive hip internal and external rotation in supine position (ICC = 0.75–0.91), while they found moderate inter/intra-rater reliability for measuring active hip internal and external rotation in seated position (ICC = 0.64–0.82) [4].

Mobile technologies mostly include a sensor of acceleration and inclination, and their software are designed to determine the small changes in these parameters. This enabled the development of clinical tools such as goniometry applications which provided a fast and simple method for measuring joint ROMs [5]. The reliability of different smartphone applications has been reported for measurement of ROM in body regions such as spine, shoulder, elbow, hip, knee, ankle, and metatarsophalangeal joints [2 , 5–8]. However, the hip joint is relatively less studied compared to other joints regarding the utility of smartphone goniometers. In their systematic review, Keogh et al. underlined the need of validity and reliability studies for smartphone goniometer applications for the hip joint [6]. Charlton et al. investigated the intra-observer reliability of a custom-made smartphone application for passive hip ROMs in a healthy male population [7]. However, measurement tools must also have criterion validity and reliability between observers at a sufficient level and no study have investigated these properties of smartphone goniometers for active hip joint ROM measurement.

“PT Goniometer” (PTG) is a smartphone goniometer application that is free and readily available in the App Store [9]. The aim of the present study was to determine inter-observer and intra-observer reliability of the PTG and investigate the concurrent validity of PTG for active hip ROMs in healthy subjects.

2 Material and methods

The present research was designed as a cross-sectional observational study. The ethical approval was obtained from the Dokuz Eylul University Ethics committee (2788-GOA, 2016/18-12). Written informed consent was obtained from all participants prior to the assessments. This study was performed in accordance with the Declaration of Helsinki.

2.1 Study design

The demographic data including age, height, weight, body mass index, leg dominance, and medical history were recorded. The method suggested by Melick et al. was used for determination of leg dominance [10]. Participants were asked “If you were to shoot a soccer ball on a target, which leg would you use?” and their answer was accepted as their dominant leg. Two physiotherapists with 3- and 4-year experiences, respectively, performed the assessments. They both had extensive experience in assessing ROM with UG and practiced with PTG for two weeks prior to the study.

2.2 Participants

A pilot study with the first ten participants was conducted to determine the necessary sample size. G^*Power 3.1.9.2 program was used for the power analysis [11]. A two tailed test with 5% of type I error, and 95% of type II error was performed. The sample size was calculated as 34 participants. All the participants were healthy undergraduate students and were recruited between June and September 2017. Inclusion criteria were: (1) being between 18–30 years old, (2) willing to participate the study. Exclusion criteria were: (1) having scoliosis, (2) chronic orthopaedic hip disorders such as previous fractures or developmental hip dysplasia, (3) suffering from chronic pain or discomfort of hip joint, (4) history of lower extremity surgery, (5) history of neurological disorders that might affect hip movements.

2.3 Instruments

A traditional plastic UG (Baseline™ goniometer), with a 360° goniometer head and 20 centimeters arms was used for UG measurements. “PT Goniometer© 2015 Mark Busman” application was downloaded into an iPhone 5s smartphone for free from App Store for smartphone measurements. PTG is an inclinometer-based application that uses the accelerometer which is built in iPhone to perceive movement and to display the result of the measurement on the screen. Same smartphone was used for all ROM assessments throughout the study.

2.4 Procedures

Hip ROMs were assessed in the following order: flexion, abduction, internal rotation, and external rotation as these movements are primarily used during daily living activities. Flexion and abduction ROMs were assessed in the supine position, while internal and external rotation ROMs were measured in the sitting position. Participants were asked to maintain the final positions of their maximal ROM for at least three seconds to allow proper measurement. Three consecutive measurements were taken and the mean values of the three measurements for each direction were used for analysis.

All participants were asked to wear shorts during the measurements and each participant was informed about the procedures prior to the actual testing. The measurements were performed on the dominant lower extremity, and only active ROMs were assessed. To determine the inter-observer reliability, two examiners performed the PTG measurements for each direction in day one. A second PTG measurement was performed by the first examiner a day after to determine the intra-observer reliability, and a third measurement was performed by the first examiner by using UG a day after the second measurement to assess the concurrent validity. Examiners were in separate rooms during the measurements, and they were not aware each other’s results. Measurements were divided into different days to prevent bias by the examiners and learning effect by the participants.

2.4.1 Hip flexion

For UG measurement, UG axis was placed over trochanter major of the femur, the stationary arm rested parallel to lateral side of the body, and the moving arm followed a line parallel to the longitudinal axis of the femur which is aligned with the lateral condyle of femur. Then, participants were asked to perform maximal active hip flexion while flexing their knee joints at the same time. The final degree observed by the examiner on the goniometer was recorded.

For PTG measurement, phone held parallel to the lateral aspect of the femur shaft in the identical starting position and then the same movement was performed by the participants.

2.4.2 Hip abduction

For UG measurement, UG axis was placed over spina iliaca anterior superior (SIAS) of the pelvis, the stationary arm rested parallel to an imaginary line between right and left SIAS, and the moving arm followed a line parallel to the longitudinal axis of the femur, aligned with the midpoint of the patella. The participants then were asked to perform maximal active hip abduction without any compensatory movement and the final degree on the goniometer was recorded.

For PTG measurement, the phone held parallel to the anterior aspect of the femur shaft in the identical starting position and the same movement was performed by the participants.

2.4.3 Hip internal and external rotation

For UG measurement, participants were in sitting position at a 90° hip flexion with their trunk erect and their arms were crossed on the chest. UG axis was placed over tuberosity of the tibia, the stationary arm rested parallel to the ground, and the moving arm followed a line parallel to the longitudinal axis of the tibia. Maximal active hip rotations were then performed in both internal and external directions. The final degree on the goniometer was recorded.

For PTG measurements, phone held parallel to the anterior longitudinal axis of the tibia in the identical starting position and then the same movements were performed by the participants.

2.5 Statistical analysis

Data analysis was performed using Statistical Package for the Social Sciences (Version 22.0, IBM, Raleigh, NC, USA) for Windows. Shapiro-Wilk test was employed to check the distribution of the data and the results showed that data were distributed normally. Therefore, means±standard deviations were used for descriptive statistics. ICC model (1, k) was used for intra-observer reliability, and ICC model (2, k) was used for inter-observer reliability. ICCs were interpreted as follows: excellent (ICC > 0.90), good (0.9 > ICC > 0.75), moderate (0.75 > ICC > 0.50), or poor (ICC < 0.50) [12]. Results were deemed as statistically significant for p < 0.05.

Standard error of measurement (SEM) values were also calculated for PTG for further investigation of reliability. SEM provides an indication of the dispersion of the measurement errors. The usual calculation of SEM is straightforward and uses formula “ $SD \times \sqrt{1 - ICC}$ ”. Furthermore, minimum detectable change at the % 95 confidence level (MDC₉₅) was computed as “ $1.96 \times SEM \times \sqrt{2}$ ” which symbolizes the importance of change necessary to provide confidence that a change is not the result of random variation or measurement error [13].

Pearson correlation coefficients (r) were used to analyze the criterion validity. Correlations were interpreted as excellent (r > 0.90), good (0.90 > r > 0.71), moderate (0.70 > r > 0.51), fair (0.50 > r > 0.31), and poor (r≤0.30) [14].

3 Results

The study was completed with thirty-four participants. Demographic characteristics of participants were provided in Table 1. The assessment scores were presented at Table 2.

Table 1
Participant Demographics (n = 34)

Demographics Mean±SD

Age (years) 22.7±3.2

Body weight (kg) 67.4±14.5

Height (cm) 172.1±8.20

BMI (kg/m²) 22.2±3.76

Left leg dominance, n (%) 7 (% 20.5)

Demographics	Mean±SD
Age (years)	22.7±3.2
Body weight (kg)	67.4±14.5
Height (cm)	172.1±8.20
BMI (kg/m²)	22.2±3.76
Left leg dominance, n (%)	7 (% 20.5)

SD: Standard deviation, kg: Kilogram, cm: Centimetres, BMI: Body Mass Index, m: Meters, n: Number.

Table 2

Descriptive Features of Range of Motion Measurements

Movement	PT 1, PTG (°) Mean±SD	PT 2, PTG (°) Mean±SD	PT 1, UG (°) Mean±SD	PT 1, retest PTG (°) Mean±SD
Flexion	118.6±8.2	118.1±7.2	118.3±8.0	118.8±7.9
Abduction	46±8.2	46.5±8.4	45.1±8.2	46.6±8.02
IR	41.2±5.3	41.0±5.1	41.5±6.0	40.9±5.2
ER	31.6±4.9	32.0±5.1	31.8±4.8	32.2±5.1

PT 1: Physiotherapist 1, PTG: PT Goniometer Application, PT 2: Physiotherapist 2, UG: Universal Goniometer, SD: Standard Deviation, IR: Internal Rotation, ER: External Rotation.

Fig. 1

Data from intra-observer and inter-observer reliability analysis including the ICC with % 95 confidence interval, SEM and MDC₉₅ were reported at Tables 3 4. Excellent inter-observer and intra-observer reliability were determined for PTG for all measured active hip ROMs. Concurrent validity of PTG was excellent for flexion, abduction, internal rotation, and external rotation ROM measurements. UG and PTG application correlated positively each other (Table 5).

Table 3

Intra-observer Reliability of the PT Goniometer Application

Movement	PT 1, PTG (°) (Mean±SD)	PT 2, PTG (°) (Mean±SD)	ICC	% 95 CI	SEM	MDC₉₅
Flexion	118.6±8.2	118.1±7.2	0.95	(0.92–0.97)	1.84	5.1
Abduction	46±8.2	46.5±8.4	0.95	(0.90–0.97)	1.84	5.1
IR	41.2±5.3	41.0±5.1	0.95	(0.91–0.97)	1.19	3.29
ER	31.6±4.9	32.0±5.1	0.91	(0.84–0.95)	1.49	4.13

PT 1: Physiotherapist 1, PTG: PT Goniometer application, PT 2: Physiotherapist 2, ICC: Intraclass correlation coefficient, CI: Confidence Interval, SEM: Standard Error of Measurement, MDC₉₅: Minimum Detectable change at the % 95 confidence level, SD: Standard deviation, IR: Internal Rotation, ER: External Rotation.

Table 4

Inter-observer Reliability of PT Goniometer Application

Movement	PT 1, PTG (°) (Mean±SD)	PT1, RT PTG (°) (Mean±SD)	ICC	% 95 CI	SEM	MDC₉₅
Flexion	118.6±8.2	118.8±7.9	0.98	(0.97–0.99)	1.16	3.21
Abduction	46±8.2	46.6±8.02	0.98	(0.97–0.99)	1.15	3.18
IR	41.2±5.3	40.9±5.2	0.97	(0.94–0.98)	0.92	2.55
ER	31.6±4.9	32.2±5.1	0.96	(0.93–0.98)	0.99	2.74

PT 1: Physiotherapist 1, PTG: PT Goniometer Application, RT PTG: Retest PT goniometer application, ICC: Intraclass correlation coefficient, CI: Confidence Interval, SEM: Standard Error of Measurement, MDC₉₅: Minimum Detectable change at the % 95 confidence level, SD: Standard deviation, IR: Internal rotation, ER: External rotation

Table 5

Validity of PTG Application

Movement	r	P
Flexion	0.93	0.001^*
Abduction	0.92	0.002^*
IR	0.92	0.001^*
ER	0.91	0.001^*

^*: p < 0.05, r: Pearson Correlation Coefficient, p < 0.05: ^*, IR: Internal rotation, ER: External rotation.

A post-hoc sample size calculation was conducted by using G^*Power 3.1.9.2 program (Software, concept and design of the University of Kiel, Germany, free Windows software by Franz) and it is demonstrated that the study had sufficient (type 2 error < 1%) power to establish validity and reliability for PTG.

4 Discussion

Clinical measurements should provide accurate, reliable, reproducible, and sensitive to change outcomes [15]. In the present study we aimed to determine the concurrent validity, inter-observer reliability, and intra-observer reliability of a smartphone application for measuring active hip ROMs in healthy participants. The PTG demonstrated excellent intra-observer (ICCs > 0.91, SEM < 1.84) and inter-observer reliability (ICCs > 0.93, SEM > 1.16) for all the directions assessed. Moreover, PTG also showed excellent correlations with UG. These results indicate that PTG may be a useful application for measuring hip ROM in clinical setting. Our ICCs and SEM values showed agreement with previous studies [7 , 16–18].

Since hip movements are critical for performing daily living activities such as squatting, walking on an inclined road or climbing stairs [21 –23], active hip ROM measurement is the main outcome in many studies which are performed in patients with hip disorders [14 , 25]. Hip ROM is also a major component of different hip scoring systems [26]. Thus, active hip ROM measurement is essential. Low SEM values obtained in this study suggests that PTG may be used to obtain active hip ROM precisely. Moreover, MDC₉₅ values can be used to analyse the change over time in patients who have different hip related pathologies or surgeries.

The gold standard for ROM assessment is radiographic imaging [27]. However, radiation exposure to the patient and being time-consuming and expensive, prevent radiography from being widely used in a clinical setting. Digital goniometers and digital imaging with computers were reliable methods for measuring range of motion as well [28, 29]. However, these methods are either expensive or not easily accessible. On the other hand, UG and PGT are both cost-effective, fast, and easily accessible tools for measuring ROM.

Being free and user-friendly are the advantages of the smartphone goniometer applications. Individuals can also use their smartphone to monitor their own progress during rehabilitation which could potentially improve the quality of self-rehabilitation or home-based physiotherapy applications by increasing the motivation [30].

Infection and/or transmission risk is an important issue regarding utilization of the smartphones in a clinical setting. Although it was not the case in the present study, contact of the smartphone with patient’s skin may be required during ROM assessments which may increase the risk of pathogen transmission. This may lead lethal consequences especially in patients following a surgery [31]. Previous studies reported that 9–25% of mobile devices were contaminated with pathogenic bacteria [32]. Taking precautions like wiping the phone with alcohol/disinfectants or placing the phone in a transparent sterile bag may lower the transmission risk.

One of the limitations of this study was the one-day interval between measurements being relatively short for avoiding learning effect. Raters may still have remembered the results obtained on the previous day. Assessing only the active hip range of motion and inclusion of only young and healthy individuals was the other important limitations of the present study. Further investigations related to validity and reliability of PTG in different populations and diseases are yet to be performed in future studies.

5 Conclusion

PTG is a valid and reliable tool for measuring active hip ROMs. This study provides additional data for the existing research regarding to the utilization of mobile technologies for measuring clinical outcomes.

Conflict of interest

None declared.

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