Test-Retest Reliability of the D and E Components of the Gross Motor Function Measure (GMFM) in Bilateral Spastic Cerebral Palsy Children

Introduction

Cerebral palsy (CP) refers to a set of persistent impairments of movement and posture, causing activity limitations, resulting from non-progressive disruptions in the developing foetal or infant brain.¹ In addition to the motor deficits linked to cerebral palsy, cognitive, behavioral, sensory, and perceptual disturbances are frequently observed.² The gross motor function classification system (GMFCS) is considered the primary system for describing functional motor activities in children with cerebral palsy. Children diagnosed with spastic cerebral palsy are more likely to have poor physical fitness (which includes muscle strength, anaerobic muscle power, aerobic capacity, and agility), compromising their daily physical functioning. The classification of cerebral palsy is based on three factors: topography, type of motor disorder, functional ability and movement disturbances. Bilateral spastic cerebral palsy falls under the topographic classification and is characterized by greater involvement of the lower limbs compared to the upper limbs. Children with cerebral palsy, along with their aerobic ability and muscle strength, are currently the focus of ongoing research.The main objective of therapy in these children is to enhance their ability to stand, walk, run, jump, and perform other vital functional tasks.³ It has been demonstrated that, compared to healthy children of the same age, children with CP exhibit gait abnormalities that increase the sub-maximal walking energy expenditure index. This results from the interplay of several ambulationrelated elements, including balance, synaptic delay, and coordination.^2,3

Several evaluation tools, such as the 'Functional Independence Measure for Children' and the 'Pediatric Evaluation of Disability Inventory', are available to evaluate the gross motor development of children with cerebral palsy. Among these, the 'Gross Motor Function Measure' (GMFM) is currently the most widely recognized and commonly utilized tool globally. The GMFM is an observational measure with criteria reference that was developed and approved to evaluate motor function in children with cerebral palsy.² The rate of change in GMFM scores is expected to correlate directly with the child's age and the degree of motor deficit in children. In practice, some clinicians choose to administrate only the dimensions most relevant to the child's current level of functional needs. The evidence supporting the validity and reliability of individual dimension scores is generally weaker than that for the overall GMFM; however, selective use of specific dimensions can increase the measure's responsiveness to change by eliminating items that are not relevant to the therapeutic intervention or are unlikely to change as a result of intervention.³

The GMFM is a crucial tool for evaluating gross motor function in children with cerebral palsy. These children often experience difficulty performing everyday tasks, like rising from a chair and moving independently. While the overall test-retest reliability of the GMFM is well established, there is little information in the literature on the test-retest reliability of the D and E components, specifically in children with bilateral spastic cerebral palsy. The purpose of this study was to determine the test-retest reliability of the GMFM components D and E in this population.

Materials and Methods

This observational study included 21 children with cerebral palsy (sample size was calculated using G power with CI of 95%), comprising both males and females who were able to understand verbal commands and had the ability to sit, stand and walk. The ethical approval for the study was obtained from the affiliated medical college institution ethical committee (JSSMC/ IEC/15/799/2016-2017). The study setting included a small bench (height 30 cm and length 100 cm), a large bench (height 50 cm and length 150 cm), two objects (small teddy bear and empty water jug), two parallel lines 20 cm apart, a straight line of 2 cm width, one ball (medium sized with a diameter of 15 cm), and height adjustable railings.

Children aged two years and above with a prior diagnosis of spastic cerebral palsy were recruited for the study. Inclusion criteria required that participants be able to sit, stand, and walk with or without assistance, comprehend and follow instructions, and have no history of spine or lower limb surgeries such as corrective procedures, muscle release, or lengthening interventions. Prior to participation, parents of all recruited children provided written informed consent, and assent was obtained from children aged ten years or older.

Procedure

The study was conducted in the pediatrics outpatient physiotherapy department, in the study setting described above. The procedure was explained to both the child and their parents, before obtaining the informed consent from the parents and verbal assent from children aged 10 years or above. The D and E components of the GMFM were administered and recorded. A retest was conducted following a washout period of no less than 96 hours and no more than 144 hours.⁴

Data analysis

Data analysis was performed using SPSS version 22.0 and significance was considered at P ≤ 0.001.The Spearman rank correlation coefficient was used to compare pairs of values.

Results

A total of 11 children with cerebral palsy were identified from the physiotherapy department's medical records for the period 2016 to 2017. Of these, parents of 10 patients agreed to participate, and 9 met the inclusion criteria. Additionally, 15 patients were included from the intervention center, of whom 12 met the inclusion criteria. In total, 21 participants completed the study, comprising 15 males and 6 females.

The participants in the study included both male and female children diagnosed with spastic cerebral palsy. The mean age of male participants was 7.66 years (SD = 2.23), while the female participants had a mean age of 7.49 years (SD = 2.20). The overall mean age of all participants was 8.08 years (SD = 2.01).

The correlation between the test and re-test was assessed using Spearman's rank correlation coefficient which is the non-parametric version of Pearson product moment correlation, where 0.00-0.19 represents 'very weak' correlation, 0.20-0.39 represents 'weak' correlation, 0.40-0.59 represents 'moderate' correlation, 0.60-0.79 represents 'strong' correlation, 0.80-1.0 represents 'very strong' or 'excellent' correlation (Table 1).

Figures 1 and 2 present a scatter plot representing the correlation between the test-retest scores of the “D” and “E” components of the GMFM, demonstrating a positive relationship between the initial and follow-up assessments. This suggests consistency and reliability in the measurement of these components across both evaluations.

The results indicate that the “D” and “E” components of the GMFM demonstrated excellent test-retest reliability. Spearman's rank correlation coefficients were r = 0.940 for D component, r = 0.951 for component E, and r = 0.911 for the combined D and E components. These values reflect a strong positive correlation between the test and retest values, with a P value of less than 0.1 in children below 10 years of age. As seen in Table 1, the test-retest reliability observed in the study was excellent.

Discussion

The purpose of this study was to evaluate the testretest reliability of the GMFM's D and E components in patients with spastic cerebral palsy. The employment of the GMFM's basal and ceiling versions, which have the most consistent components, varies depending on the situation. There is item reliability and a rapid analysis of the GMFM. In this specific study, we examined the functions for clinical decision making regarding assessment frequency in relation to patient response and test-retest reliability.⁵ Due to the inability to move freely, people with cerebral palsy are limited in their ability to engage in physical activities and to perceive their surroundings. In addition, CP impairs the development of movement concepts, social interaction, and perceptual or sensory functions. As a result, over time, CP not only causes mobility abnormalities but also limits involvement in a variety of activities. The extent of activity restriction is directly correlated with the degree of impairment.^6,7 Therefore, when examining the gross motor function in children with cerebral palsy, it is essential to consider both the level and quality of a child's motor function performance in activities of daily life.

Clinical practice requires evaluation instruments with high levels of validity, reliability, and accuracy. The accuracy and outcomes of the instrument differ based on the technique, setting, and assessor enforcement. Several tools are available for evaluating children's motor function. The GMFM scale demonstrates strong reliability and content validity, making it a valuable tool for understanding motor development in children with cerebral palsy. It also possesses good psychometric qualities.⁷

The Gross Motor Function Measure (GMFM) is a psychometrically sound assessment instrument designed to evaluate changes in gross motor function in children with cerebral palsy, between the ages of five months and sixteen years.⁸ In clinical research, it is frequently utilized as a motor function measure. When compared to other rehabilitation measures, the GMFM scale is a crucial validation benchmark. It has been widely employed to gauge changes in therapeutic efficacy. Similar findings were observed in the current investigation.⁹

During the second trial, four children demonstrated the largest score difference- up to six points in three subcomponents of the E dimension. These variations were attributed to factors like - one child had a headache, two were experiencing symptoms of cold, and one was distracted due to the absence of sibling. These significant variations imply that the child's physical and mental state on the day of assessment may have an impact on the GMFM results. The timing of test administration was also crucial as some children were assessed once in the morning and again in the afternoon during the investigation, which contributed to variation in the results. Therefore, it is crucial to complete the examination within a consistent and appropriate timeframe before making clinical decisions. This suggests that D and E components can be used independently to assess children with cerebral palsy.

Limitations: Some children became easily distracted during the assessments. The timing of the tests also played an important role; children who were tested in the morning and then retested in the afternoon experienced greater difficulty completing the assessments. Additionally, the presence of parents influenced cooperation, as some children were less cooperative with the assessor when their mother was absent during testing. 

Implications: Given the excellent reliability demonstrated for the D and E components of the GMFM, these components can be used as assessment tools for children with CP who have difficulties with gross motor functions, but have already achieved skills measured by A, B and C components. This approach can save time for both the assessor and the client. 

Conclusion

This observational study, involving twenty-one participants, demonstrated good test-retest reliability for the D and E components of the GMFM in children with bilateral spastic cerebral palsy. These components of the GMFM can be administrated individually in clinical settings to assess mobility in children with cerebral palsy.

Conflict of Interest

Nil

Funding Source

Nil