Probability of walking, wheeled mobility, and assisted mobility in children and adolescents with cerebral palsy

Abstract

Aim  Our aim was to describe how the probability of walking, wheeled mobility, and assisted mobility changes with environmental setting and age in children and adolescents with cerebral palsy (CP).

Method  The parents of a population-based sample of 642 children and adolescents (360 males, 282 females; age range 16mo–21y) reported their children’s mobility at home, school, and outdoors at 6- or 12-month intervals a mean of 5.2 times. Generalized mixed-effects analyses were used to model the probabilities.

Results  By age 3 years, children with motor function classified as level I according to the Gross Motor Function Classification System (GMFCS) walked in all three settings. Children/adolescents classified as level V used assisted mobility, with a small number using wheeled mobility. In the case of children classified as GMFCS level II, the probability of walking varied with the environmental setting, which, at age 18, is outdoors 90% of the time. Among children classified as GMFCS level III, the probability of walking was highest at age 9 at school (68%), and at age 18 was approximately 50% in all three settings. Among children/adolescents rated as GMFCS level IV, the probability of wheeled mobility increased with age and, at age 18, 57% of mobility took place outdoors.

Interpretation  The results provide evidence that age and environmental setting influence method of mobility of children/adolescents with CP. The method that is preferred in one setting may not be preferred in another setting or at another age.

List of Abbreviations

ASQME

Adolescent Study of Quality of Life, Mobility, and Exercise

ICCs

Intraclass correlation coefficients

Cerebral palsy (CP) describes a group of disorders of posture and movement that occur as a result of a non-progressive disturbance in the developing fetal or infant brain.¹ The Surveillance of Cerebral Palsy in Europe has reported that the current prevalence of CP is 2.12 to 2.45 per 1000 live births.² United Cerebral Palsy³ estimates that in the USA 9000 infants and preschool-age children are diagnosed with CP each year and that there are currently 764 000 children and adults with CP in the USA. Although the neurological disturbance associated with CP is non-progressive, secondary musculoskeletal impairments, pain, increased body mass, and physical fatigue are thought to contribute to changes in motor function in adolescents and adults with CP that may include a decline in walking.^4–9 Day et al.¹⁰ performed a retrospective analysis of individuals with CP who received services from the state of California from 1987 to 2002 and reported that children who walked and climbed stairs at age 10 had a 23% chance of experiencing a decline in gross motor abilities at age 25.

Mobility in daily life is influenced by environmental factors. Physical and temporal features of the environment vary across home, school, work, outdoor, and community settings. People typically travel longer distances over more varied surfaces when outdoors and in the community. Temporal features that influence individual preferences for mobility include whether other people are moving about (i.e. this may present a challenge) and time constraints.¹¹ The results of a population-based study indicate that environmental setting influences the methods of mobility used by children with CP.^11–13 Compared with the school setting, children aged from 4 to 12 years have been found to be less dependent on physical assistance for mobility at home and more dependent on physical assistance for mobility when outdoors or in the community.¹³ Tieman et al.¹² examined changes in the mobility methods used by 62 children with CP over a 3- to 4-year period (at mean ages of 8y 4mo, 10y 5mo, and 12y 1mo). At the second assessment, the number of children who walked was found to have increased. Conversely, at the third assessment, the number of children who used wheeled mobility was found to have increased. Differences in mobility methods used in home, school, and outdoor/community settings were most pronounced among children with CP whose motor function was classified as GMFCS levels II to IV.^11,14

The purpose of this study was to provide a longitudinal description of how the probability of walking, using wheeled mobility, and using assisted mobility changes in children and adolescents with CP depending on environmental setting and age. Knowledge of the influence of environmental setting and age on mobility has implications for long-term planning and interventions to optimize safe and efficient mobility.

Method

Participants

The participants were 642 children and adolescents with CP (360 males, 282 females; age range 16mo–21y) who participated in the Ontario Motor Growth study of the development of gross motor function.¹⁵ The accessible population was 2226 children with CP who were less than 12 years of age in 1996 and receiving services from regional centres of the Ontario Association of Children’s Rehabilitation Services. A stratified random sampling procedure was used to ensure representation of all ages and GMFCS levels. Children were eligible if they had a diagnosis of CP made by a physician, or if CP was strongly suspected based on a physical therapist’s evaluation of the child’s posture and movement and the presence of neuromuscular impairments. Participants who were aged 11 to 17 years in 2002 were eligible for a subsequent Adolescent Study of Quality of Life, Mobility, and Exercise (ASQME). We were able to contact 312 of the 642 participants, of whom 224 (72%) contributed additional data to the current study.

Both studies were approved by the McMaster University Research Ethics Board. A parent provided informed consent and each adolescent provided informed consent or assent, if possible. For the second study, the participants themselves provided informed assent or consent. At the time of entry into the Ontario Motor Growth study, 182 children were classified in GMFCS level I, 78 children in level II, 113 children in level III, 136 children in level IV, and 133 children were in level V. The youngest child at the start of the Ontario Motor Growth study was 16 months old, whereas the oldest participants at the end of the ASQME study were 21 years old.

Measures

Gross Motor Function Classification System

The GMFCS is a five-level system that was developed to classify the functional abilities of children with CP who are 12 years of age and younger. Distinctions between GMFCS levels are based on functional limitations, the need for assistive mobility devices (walkers, crutches, canes) or wheeled mobility, and, to a lesser extent, quality of movement. The GMFCS has evidence of validity, stability, and interrater reliability.^14,16

Usual method of mobility

A questionnaire on usual method of mobility completed by parents was developed for the Ontario Motor Growth study.¹³ The questionnaire instructs parents as follows: ‘Please use an X to mark the box beside the one way your child/adolescent most often moves around for each setting: home (indoors), school or work (indoors), and outdoors.’ The response options are ‘carried by adult’, ‘takes steps with adult assistance’, ‘pushed in a wheelchair by an adult’, ‘moves on floor’, ‘walks holding on to wall or furniture’, ‘walks with a walking aid’, ‘walks alone without any assistance’, ‘propels self in regular wheelchair’, and ‘operates a battery-powered motorized wheelchair’. The emphasis on one method reflects the reality that individuals with CP may use more than one method within each environmental setting, but that we are interested in the most common method used.

Procedure

Physical therapists classified each child’s GMFCS level at the first data collection point of the Ontario Motor Growth study. In the Ontario Motor Growth study, usual method of mobility was reported by a parent every 6 months for children less than 6 years of age and every 12 months for children aged 6 years or over. In the ASQME study, usual method of mobility was reported by a parent every 12 months. For the total sample of 642 participants, usual method of mobility was reported a mean of 5.2 times (SD 2.2). For the subset of 224 participants who participated in both studies, the usual method of mobility was reported a mean of 7.9 times (SD 1.2). The total number of times usual method of mobility was reported was 3387 (for a detailed breakdown, see Table SI, supporting information, published online).

Data analysis

Response options for usual method of mobility were collapsed into three methods that we propose represent differences in mobility that are likely to be meaningful in the daily lives of children and adolescents with CP. The methods are walks (‘walks holding on to wall or furniture’, ‘walks with a walking aid’, ‘walks alone without any assistance’), wheeled mobility (‘propels self in regular wheelchair’, ‘operates a battery-powered motorized wheelchair’), and assisted mobility (‘carried by adult’, ‘takes steps with adult assistance’, ‘pushed in a wheelchair by an adult’, ‘moves on floor’). The response option ‘moves on floor (rolling, creeping, and crawling)’ was reported only in the home setting and primarily at younger ages. With the exception of floor mobility, the distinguishing feature of the method ‘assisted mobility’ is the need for hands-on help from another person. The three mobility methods are treated as ordinal distinctions that are assumed to reflect important underlying variations in the independence afforded by the method.

Children’s GMFCS levels were based on the first data collection point. This decision was made to reflect the clinical reality that parents seek prognostic information about their child’s outlook for walking from the time CP is first diagnosed.¹⁵ Evidence of the stability of the GMFCS supports the decision. During the Ontario Motor Growth study, 73% of children remained in their initial GMFCS levels for all subsequent ratings. The weighted kappa coefficient between the initial and last rating was 0.84 for children aged less than 6 years and 0.89 for children older than 6 years, indicating excellent chance-corrected agreement.¹⁶

For each GMFCS level and environmental setting, the observed frequencies of each method of mobility were plotted to determine the number of children who used each method at a particular age. Generalized mixed-effects analyses were used to model the probabilities of the ordinal mobility methods as a function of age. These analyses were conducted separately for each setting (home, school, outdoors) at each GMFCS level. Complete details of the generalized mixed-effects analyses are provide in Appendix S1 (supporting information, published online), and only a conceptual overview is given here. The ordering of the mobility methods was represented by using a cumulative logit link function, estimated within proportional odds models. Cumulative logits are a standard method to link an ordinal outcome to a linear set of predictors.^17,18 A proportional odds model assumes that the effect of age is the same for each mobility method. The model includes regression parameters for an intercept, age, age-squared, and age-cubed, which together constitute the curvilinear model for change over age. The model was chosen for its flexibility in describing change, rather than for explanatory goals, and so we retain all three terms in all models, regardless of their significance. Instead, 95% confidence intervals (CIs) are reported for all coefficients.

The generalized mixed-effects models account for the longitudinal study design by including a random-effect for the intercept.¹⁸ This allows for the prediction of each child’s overall level of mobility, and appropriately adjusts for the non-independence of multiple measurements for each child. The estimated variance of the random intercepts expresses the degree of variation among children of the same age and GMFCS level. Intraclass correlation coefficients (ICCs) were calculated from the estimated variance to determine the degree of consistency of mobility method within children after accounting for age. To facilitate interpretation of the model results, the estimated marginal probabilities of the three mobility methods were plotted as a function of age. Estimated marginal probabilities are easier to interpret than the estimated parameters, which are on the logit scale.¹⁹

Results

For children and adolescents in GMFCS levels I and V, the data are notable for the limited variability in usual method of mobility by age. This is illustrated by the histograms for the outdoor setting (Fig. 1). By age 3, almost all children in GMFCS level I walked in all three environmental settings. At any age after 7, the number of children or adolescents classified as level I whose usual method of mobility in the outdoor setting was not walking did not exceed 4. Conversely, only a small number of children and adolescents in GMFCS level V moved without the physical assistance of another person. Between the ages of 7 to 8.9 years, (10%) 12 children in GMFCS level V used powered mobility at school and outdoors. Between the ages of 13 to 14.9 years, nine participants (17%) classified as GMFCS level V used powered mobility at school and outdoors. The lack of variability in method of mobility among children and adolescents in GMFCS levels I or V makes further modelling of these data difficult and uninformative.

Figure 1.  Histograms of number of children and adolescents with motor function classified as Gross Motor Function Classification System levels I or V who used each method of mobility.

The estimated coefficients from the longitudinal proportional-odds models of the ordinal mobility methods for levels II to IV are included in Appendix SI and Table SII (supporting information, published online), along with their 95% CI. The ICCs vary from 0.63 to 0.82 and indicate that, after adjusting for age, method of mobility is highly consistent within children over time. Consistency is generally highest for the home environment and lowest for the school environment, across GMFCS levels.

Figures 2 to 4 present the estimated probabilities of each mobility method as a function of age and environmental setting among children and adolescents classified as GMFCS levels II to IV. Although all the models are based on all the available data, the estimated probabilities are plotted only between the ages of 3 and 18, as the number of available data is greatest for these ages. Because the usual mobility methods are mutually exclusive, the predicted probabilities sum appropriately to 1.0 (100%) across mobility methods, at any given age.

Figure 2.  Estimated probabilities of each mobility method as a function of age and environment among children and adolescents with motor function classified as Gross Motor Function Classification System level II.

Figure 3.  Estimated probabilities of each mobility method as a function of age and environment among children and adolescents with motor function classified as Gross Motor Function Classification System level III.

Figure 4.  Estimated probabilities of each mobility method as a function of age and environment among children and adolescents with motor function classified as Gross Motor Function Classification System level IV.

For children classified as level GMFCS II, the probability of walking at age 4 varies from 39 (outdoors) to 76% (school); at age 9 it ranges from 75 (outdoors) to 93% (school); and at age 18 the probability is 93% at school, 90% outdoors, and 78% at home. At home, the probability of requiring physical assistance increases to 22% at age 18.

For children classified as GMFCS level III, the probability of walking increases from age 4 and peaks at age 9 in the school setting (68%), at age 11 in the outdoors setting (54%), and at age 14 in the home setting (52%). At age 18 the probability of walking is about 50% in all three settings. At home, adolescents whose usual method of mobility is not walking are more likely to move with physical assistance than to use wheeled mobility. At school and outdoors, adolescents whose usual method of mobility is not walking are almost as likely to use wheeled mobility as to use assisted mobility.

Among children and adolescents classified as GMFCS level IV, the probability of using wheeled mobility increases with age. At home, assisted mobility has the highest probability at all ages. At age 7 (school) and age 12 (outdoors), children have an equal probability of using wheeled mobility or assisted mobility. At age 18, the probability of using wheeled mobility is 57% outdoors, 45% at school, and 37% at home.

Discussion

The results provide evidence that the usual method of mobility of children and adolescents with CP is influenced by environmental setting and age. The probability estimates were modelled from longitudinal data from a population-based sample and, therefore, are likely to be generalizable to populations elsewhere whose resources and services are similar to those in Ontario, Canada. The findings might not apply to communities across the world where services and assistive technology are limited. Performance of mobility, what an individual does in daily life, reflects the influence of environmental and personal factors. Most research in CP is based on motor capacity, that is what an individual can do on a standardized measure administered in a clinical setting. Our interest in performance of mobility coincides with the International Classification of Functioning Disability and Health,²⁰ in which environmental and personal factors are important determinants of health and function.

It is important to consider the limitations of the study when applying the results. For consistency, parents reported usual methods of mobility at all ages. Parent report may have been less accurate for the school setting, where they had less opportunity to observe their children. Parents were asked to report the one way that their child most often moves around, which reflects the possibility that some children and adolescents may use more than one method within a setting. The probability estimates for assisted mobility in the home setting are confounded by the inclusion of children who use floor mobility. Generalized mixed-effects analyses were used to model the probability estimates. The estimated probabilities may be less precise at the youngest and oldest ages.

For adolescents classified as GMFCS level I or II, the results are encouraging given the concern that walking may decline among adolescents and young adults with CP.^4–10 Descriptive data indicate that, for children classified as GMFCS level I, walking is the usual method of mobility by age 3, and they continue to walk in all environments throughout adolescence. For children classified as level II, the probability of walking is high in all settings by age 9. In contrast, children and adolescents classified as GMFCS level III demonstrate variability in method of mobility in all settings. Before age 5, the estimated probability of walking for children in level III is <50% in all settings and does not exceed 60% at home or outdoors at any age. The findings for children and adolescents rated as GMFCS level III are not surprising, particularly for the outdoors setting. Children and adolescents rated as level III use an assistive device such as a walker, crutches, or cane for stability and balance which may not be efficient or effective for long distances and uneven terrain, especially when attempting to keep up with peers.

For adolescents in GMFCS level II and children in GMFCS level III, the probabilities of assisted mobility at home may reflect features of the home environment and inclusion of floor mobility in the category ‘assisted mobility’. Previously we reported that, between the age of 4 and 12 years, 47% of level III participants used floor mobility (rolling, creeping, crawling) as their usual method of mobility at home.^11,13 A purposive sample of 10 young adults age between 17 and 20 years, who were also participants in this study, expressed preferences for mobility at home such as crawling on hands and knees or walking using furniture or walls for support that may not be safe, practical, or socially appropriate at school or in the community.²¹

For children and adolescents in GMFCS level IV, the higher probability of wheeled mobility with age reflects the use of powered mobility, especially at school and outdoors. Children and adolescents classified as level IV have impairments in motor control of trunk, arm, and leg movements that preclude walking and manual propulsion of a wheelchair as effective methods of mobility. Research indicates that children as young as 2 and children with severe motor impairments are capable of operating a powered wheelchair.^22,23 The lower probability of wheeled mobility at younger ages for children in GMFCS level IV most likely reflects several factors, including family and professional perspectives regarding powered mobility, health insurance, and financial resources.

The results have implications for long-term planning, clinical decision-making, and family-centred services. Discussion of mobility options with children and families and involving children in decision-making is recommended, with the understanding that the method of mobility that optimizes participation in one setting may not be the preferred method in another setting. Efficiency, safety, self-sufficiency, and environmental features such as distance and time requirements are important considerations when making decisions regarding goals and interventions for mobility. Therapists are encouraged to evaluate features of everyday environments when planning interventions to improve mobility. For many children and adolescents classified as GMFCS levels III or IV, powered mobility may enhance participation at school and outdoors. Children and adolescents classified as GMFCS level V are primarily carried or transported in a wheelchair at all ages. This has implications for injury prevention, including instruction of caregivers about body mechanics, proper transfer techniques, environmental modifications, and assistive technology to reduce physical demands.