Validity and reliability of smartphone-based pelvic rotation evaluations of children with cerebral palsy while sitting,standing,and standing on one leg

Abstract

PURPOSE:

We explored the test-retest reliability of pelvic rotation measured using a smartphone and established criterion-related validity by analyzing simple linear regression between pelvic rotation data obtained using the smartphone and those measured by a palpation meter.

METHODS:

We recruited 12 children with cerebral palsy (CP) (7 boys and 5 girls) and measured pelvic rotation using a smartphone application and a palpation meter in the sitting, standing, and one-leg standing positions. Test-retest reliability was evaluated by calculating intraclass correlation coefficients (ICCs); simple linear regression was analyzed to explore the relationships between smartphone and palpation meter data.

RESULTS:

In terms of the test-retest reliability of pelvic rotation measured by the smartphone, the ICCs ranged from 0.85 to 0.95. A positive linear correlation was found between smartphone and palpation meter data.

CONCLUSIONS:

We confirmed that measurement of pelvic rotation using a smartphone was reliable when children with CP were in the sitting, standing, and one-leg standing positions. In addition, pelvic rotation measured using the smartphone correlated significantly with that measured using a palpation meter.

1. Introduction

Pelvic rotation is closely associated with both trunk motion and lumbar spine curvature [1]. When the pelvis is rotated anteriorly, lordosis of the lumbar vertebrae increases in the sagittal plane; when the pelvis is rotated posteriorly, lumbar kyphosis increases [2]. Pelvic asymmetry is associated with changes in trunk posture, scoliosis [3], increased lumbar spine stress [4], and leg length differences [5]. In children with cerebral palsy (CP), the pelvis is excessively tilted posteriorly when sitting and excessively tilted anteriorly when standing [6]. Additionally, physical activities such as sitting and standing are limited by excessive pelvic rotation [6, 7]. Therefore, it is important to measure pelvic rotation in children with CP.

Pelvic rotation is frequently assessed in the sitting, standing, and one-leg standing positions in ambulatory children with CP since these postures are all adapted when performing daily activities [8, 9, 10]. A palpation meter is frequently used to obtain pelvic rotation data which are reliable when recorded in healthy adults [9]. Krawiec et al. [11] investigated the reliability of a palpation meter on 24 male and 20 female collegiate athletes. Test-retest reliability was reported as $r=$ 0.99 and standard error of measurement (SEM) ranging from 0.44 ${}^{\circ }$ to 0.47 ${}^{\circ }$ . However, there has been no previous study on the reliability of the palpation meter in children with CP. In addition, smartphone-based measurements provide an easy and convenient method to measure the rotation of the pelvis. However, there has been no research on the validity and reliability of smartphone-based pelvic rotation evaluations in children with CP.

The minimal detectable change (MDC) is the smallest difference detectable above the measurement error [12]. Azevedo et al. [9] studied the MDC of measuring pelvic rotation using a palpation meter. The MDC of pelvic rotation ranged from 1.5 ${}^{\circ }$ to 4.0 ${}^{\circ }$ in twenty healthy adults. However, the MDC of pelvic rotation detected using a smartphone has not yet been described for children with CP. Therefore, the purpose of this study was to investigate the test-retest reliability of pelvic rotation measured using a smartphone, and to estimate the MDC of such rotation in children with CP. The secondary purpose of this study was to establish criterion-related validity by analyzing simple linear regression between pelvic rotation data derived using a smartphone and a palpation meter in children with CP.

2. Methods

2.1 Children

We recruited 12 children with CP (7 boys and 5 girls, mean age, 9.0 $\pm$ 2.1 years; mean height, 132.9 $\pm$ 10.4 cm; mean weight, 28.2 $\pm$ 7.9 kg) from Gyeongsangbuk-do, Republic of Korea. The required sample size was established using G-Power power analysis software (ver. 3.1.; University of Dusseldorf, Dusseldorf, Germany). The target sample size was nine, based on a correlation of 0.80, a power (1–the $\beta$ error) of 0.80, and an $\alpha$ error of 0.05, as revealed by pilot data. The incusion criteria were based on (1) CP diagnosed by a neurologist; (2) age 6–15 years; (3) level I-III on the Gross Motor Function Classification System (GMFCS); (4) an ability to understand the researcher and follow instructions; and, (5) the absence of any musculoskeletal injury or surgery of the lower limbs over the past 12 months. This experimental protocol was approved by the Institutional Review Board (2018-02-008). All participants received information on the research protocol from the lead researcher.

2.2 Examiners

A single examiner with 7 years of experience in pediatric physical therapy performed all measurements. To reduce measurement error, the examiner was trained in pelvic rotation assessment in the sagittal plane by a senior researcher with 20 years of experience in pediatric physical therapy.

2.3 Apparatus

The palpation meter featured an angle-level inclinometer with a magnetic base and two caliper arms (Acuangle; Isomed, Portland, OR, USA). The device was 93 mm long $\times$ 100 mm wide $\times$ 15 mm high, and afforded an accuracy of 0.083 ${}^{\circ }$ . The inclinometer pole revolved in hydraulic oil upon tilting. In addition, double annular gradations provided accurate measurements. A clinometer linked to a bubble-level Android smartphone (Plaincode Software Solutions, Stephanskirchen, Germany) was also used to measure pelvic rotation. The required application quantifies tilt in a visual manner. In general, a positive score for both a palpation meter and the smartphone application reflect anterior pelvic rotation and a negative score for both a palpation meter and the smartphone application mean posterior pelvic rotation.

Table 1

Pelvic rotation data

Positions	Smartphone		Palpation meter		Linear regression
	Mean	SDs	Mean	SDs	R	R ${}^2$	p
Sitting	$-$ 18.91	4.60	$-$ 16.71	2.94	0.797	0.635	0.002
Standing	14.83	4.41	10.58	4.83	0.739	0.546	0.006
One-leg standing	$-$ 8.58	3.94	$-$ 7.33	2.83	0.728	0.531	0.007

SDs: standard deviations.

Figure 1.

The flow chart for pelvic rotation measurements.

2.4 Procedure

All children participated on two occasions (test occasion, T1; retest occasion, T2), which were two weeks apart. Pelvic rotation in the sagittal plane derived using both the palpation meter and the smartphone was obtained with participants in each of three positions (sitting, standing, and one-leg standing). For examining pelvic rotation, the children were asked to sit on a therapeutic table with thigh support, without back and feet support, and also were to assume a comfortable or preferred sitting position according to Bigongiari’s protocols [13]. When standing, the children were asked to stand with their feet aligned at shoulder width and to look at a red dot attached to a wall 2 m distant, to reduce trunk sway. In the one-leg standing position, the children were asked to stand with the dominant leg on the floor and to maintain the opposite hip at 45 ${}^{\circ }$ of flexion. An inclinometer was attached to the lateral thigh to confirm such flexion. For standing- and one leg standing-position, the children were required to cross their arms in front of the chests. When independent practices were not possible, children were allowed to use assistive tools. When measuring pelvic rotation using the palpation meter, the examiner palpated landmarks (the anterior superior iliac spine [ASIS] and the posterior superior iliac spine [PSIS]) and marked them with black dots [8], and then placed the caliper tips at the ASIS and PSIS. When measuring pelvic rotation using the smartphone, the examiner identified the sacral vertebrae S1–S2 and marked them with black dots. The smartphone was placed on a line connecting S1 and S2 [14]. Calibrations were performed prior to measurement to ensure that the experimental values were stable. All measurements were performed three times and the means used in analysis. The flow chart for pelvic rotation measurements is shown in Fig. 1.

2.5 Statistical analysis

PASW software (ver. 20; Norusis/SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. Statistical significance was defined by a two-tailed $p$ -value $<$ 0.05. Intraclass correlation coefficients (ICCs) were calculated to determine the test-retest reliability of pelvic rotation assessments in the sitting, standing, and one-leg standing positions. We used ICC (3,1) model to evaluate reliability between the first and second measurements. The SEM was: SD $\times \surd (2[1-r])$ . The MDC was estimated by reference to the SEM, as follows: z score $\times \sqrt{2}\times$ SEM $=$ 1.96 $\times \sqrt{2}\times$ SD $\times \surd (2[1-r])$ . The z score (1.96) was based on the 95% confidence interval for the test-retest reliability coefficient [15]. The relationship between smartphone and palpation meter data were analyzed using a simple linear regression [16].

Table 2

The test-retest reliability, standard error of measurement (SEM), and minimal detectable change (MDC) of pelvic rotation

Positions	Reliability (test-retest)		SEM (degree)		MDC (degree)
	Smartphone	Palpation meter	Smartphone	Palpation meter	Smartphone	Palpation meter
Sitting	0.95	0.96	1.02	0.58	2.01	1.15
Standing	0.94	0.96	1.08	0.96	2.11	1.89
One-leg standing	0.85	0.86	1.52	1.06	2.99	2.07

3. Results

The means and standard deviations (SDs) of pelvic rotation measured by the smartphone and palpation meter in the sitting, standing, and one-leg standing positions are shown in Table 1. The test-retest reliabilities (ICCs) of smartphone-measured pelvic rotation were 0.95 ( $p<$ 0.001), 0.94 ( $p<$ 0.001), and 0.85 ( $p=$ 0.002) in the sitting, standing, and one-leg standing position, respectively. The SEMs were 1.02, 1.08, and 1.52 in the sitting, standing, and one-leg standing positions, respectively, and the corresponding MDCs were 2.01, 2.11, and 2.99 (Table 2). The linear regression analysis yielded $R=$ 0.797 with $R^2$ of 0.635 ( $p=$ 0.002), $R=$ 0.739 with $R^2$ of 0.546 ( $p=$ 0.006), and $R=$ 0.728 with $R^2$ of 0.531 ( $p=$ 0.007) in the sitting, standing, and one-leg standing positions, respectively (Table 1) (Figs 2–4).

Figure 2.

Linear regression analysis between smartphone and palpation meter data in sitting position.

Figure 3.

Linear regression analysis between smartphone and palpation meter data in standing position.

Figure 4.

Linear regression analysis between smartphone and palpation meter data in one-leg standing position.

4. Discussion

Pelvic rotation measured using the smartphone was $-$ 18.91 ${}^{\circ }$ (4.60 ${}^{\circ }$ ), 14.83 ${}^{\circ }$ (4.41 ${}^{\circ }$ ), and –8.58 ${}^{\circ }$ (3.94 ${}^{\circ }$ ) in the sitting, standing, and one-leg standing positions, respectively. Azevedo et al. [9] reported pelvic rotations of approximately –17.7, 6.4, and 1.2 ${}^{\circ }$ in the three positions in healthy participants. Similarly, Koumantakis et al. [14] found that the standing pelvic rotation was about 20.64 ${}^{\circ }$ in college students. The pelvic rotation data of children with CP showed greater compared with healthy participants. We believe that these findings are due to weakening of core muscles, muscle imbalance, and orthopedic concerns in children with CP [17].

Test-retest reliabilities were excellent in the sitting, standing, and one-leg standing positions (ICCs $=$ 0.95, 0.94, and 0.85). No previous study directly compared pelvic rotation among different positions in children with CP. However, some studies found that use of a palpation meter to evaluate pelvic rotation of patients in the standing and sitting positions afforded excellent reliability [8, 9]. Our results are similar to those of previous studies; pelvic rotation measurement was reliable in children with CP.

The MDC is affected by measurement reliability and responsiveness [15, 16]; the MDC is the minimal change that can be detected by the measuring instrument beyond measurement error [17, 18]. The analyses show that the MDC was 2.01, 2.11, and 2.99 in the sitting, standing, and one-leg standing positions; therefore, when the change in pelvic rotation between two measurements reach these parameters, the clinicians might interpret the changes as reliable beyond measurement error. A strong linear relationship was evident between pelvic rotation measured using both a palpation meter and the smartphone. Generally, it is considered that a correlation coefficient $⩽$ 0.30 reflects a weak relationship, a value $⩾$ 0.50 denotes a moderate relationship, and a coefficient $⩾$ 0.70 corresponds to a strong relationship [18]. Our results found that a smartphone was valid and reliable to measure pelvic rotation in children with CP. For clinicians, the present study is able to provide an alternative measurement strategy for pelvic rotation in children with CP.

Our study had certain limitations. First, we calculated only short-term MDC. Future studies should calculate minimal clinically important differences over the long term. Second, because the main purpose of this study is to compare pelvic rotation data obtained using a smartphone and those measured by a palpation meter, we could only measure test-retest reliability. Future studies will need to estimate inter-rater reliability for smartphone-based pelvic rotation in consideration of the risk rater errors. Finally, we measured pelvic rotation only in children with CP. Future studies should include typically developing children.

5. Conclusion

We confirmed that measurement of pelvic rotation using a smartphone is reliable in children with CP in the sitting, standing, and one-leg standing positions. Additionally, pelvic rotation values measured using the smartphone correlated significantly with those assessed using a palpation meter. Thus, the smartphone afforded excellent criterion-related validity. Measurement of pelvic rotation using a smartphone is easy, fast, and cost-effective in clinical settings [19]. Our findings contribute preliminary evidence of pelvic rotation evaluations using a smartphone in rehabilitation protocols for children with CP.