Should the Gross Motor Function Classification System Be Used Outside of Cerebral Palsy?
KEEPING CURRENT © MEGAN TOWNS & PETER ROSENBAUM, 2018
The Gross Motor Function Classification System (GMFCS) (1,2) is a classification tool used to describe levels of gross motor functioning of children with cerebral palsy (CP). Because of the tool’s accuracy in classifying children with CP, some researchers have attempted to use the GMFCS to describe functional mobility of people with other conditions. Here we explain why the GMFCS should not be used outside the domain of CP. To start, it is important to explain some of the basics of measurement and then to describe the GMFCS in more detail.
What is a measurement tool?
Every measurement tool is designed to do one or more particular jobs. For instance, a measurement tool can be used to do one or more of 4 tasks:
- Describe a group of people who have certain characteristics
- Discriminate/differentiate between people with different levels of ability
- Evaluate change over time or in response to a treatment
- Predict a person’s future abilities
What is a measurement?
A measurement is a process of answering a specific question that requires:
- The right tool(s) that are …
- Used the right way…
- By people who know how to do this…
A measurement tool may be a good tool – but is the user capable of using that tool?
- Are they trained to use the tool, and are they accurate in their use?
- Are they using the tool as it is meant to be used?
Since tools are designed to do different jobs, using the wrong tool, or the right tool in the wrong way, may not help get the job done or help find the answer to the user’s specific question.
What measurement tool should be used?
Before deciding on the best tool for the job, we start by looking at the job itself. Another way of thinking about this is to ask “What’s the Question That I Want to Answer?” We call this the WTQ issue.
What is the Gross Motor Function Classification System and what does it do?
Since its publication in 1997, the Gross Motor Function Classification System has become the international language to classify gross motor function of children with CP. It has enhanced communication between families and professionals by providing standardized descriptions of gross motor function for five functional ability levels that are described within each of five age groups (2) (more about this later).
Unlike other classification methods that had been proposed, GMFCS focuses on (3):
- FUNCTION, which is more important to clinicians and families than neuropathology (e.g., muscle tone, reflexes, pathophysiology)
- WHAT PEOPLE CAN DO, not what they cannot do! Describing what kids cannot do provides little information about what they can do.
- USUAL PERFORMANCE in day-to-day lives, not performance under optimal condition
How was the Gross Motor Function Classification System created?
Its developers examined numerous videos and clinical notes of children and teens with CP to understand and characterize the key differences in their functional abilities.
From this information, they created detailed descriptions that highlight distinctions between adjacent levels that would then illustrate the way that individuals with cerebral palsy function.
- For example: children [with CP] aged 2 to 4 years in Level II are described as follows: ‘Children floor sit but many have difficulty with balance when both hands are free to manipulate objects. Movements in and out of sitting are performed with- out adult assistance. Children pull to stand on a stable surface. Children crawl on hands and knees with a reciprocal pattern, cruise holding on to furniture, and walk using an assistive mobility device as preferred method of mobility.’ (3)
These descriptions were then incorporated into the descriptions in the GMFCS.
Why is it helpful to classify based on gross motor function?
A review of the published literature completed in 1994 found many different approaches had been suggested for classifying people with CP, including classifying on the basis of: parts of the body most involved; muscle tone; reflexes; voluntary movement control; ability to walk or wheel; and pathophysiology.(1)
While these classification methods may help with making the diagnosis of CP, they did not provide much information about how children and youth with CP were able to function in their day-to-day lives.3 The term ‘gross motor function’ describes movements that people use to get about indoors and outdoors. Sitting, crawling, walking, going up and down stairs, and getting in and out of a car are all examples of gross motor function activities. Children with CP vary widely with respect to their gross motor function, and it is much more helpful to differentiate children on the basis of their functional abilities than on the severity of their motor impairments or limitations.
To address this information need, a team of CanChild researchers set out to develop the Gross Motor Function Classification System for use with children with CP.
What does the Gross Motor Function Classification System look like?
The GMFCS is a categorization system based on description of 5 ability levels I to V (I = highest level of gross motor functioning; V = lowest level of gross motor functioning) (1,2). It contains 5 distinct age bands (before 2nd birthday, between 2nd and 4th birthday, between 4th and 6th birthdays, between 6th and 12th birthdays, and between 13th and 18th birthdays). These age bands reflect functional ability changes that may occur during development. Each age band includes descriptions for each of the 5 functional levels (I to V) (1,2). (Note the use of Roman numerals, not numbers, for these levels.)
How is the Gross Motor Function Classification System Used?
Like other classification systems, the GMFCS is used to categorize an individual, and to group individuals according to characteristics described by the system. In this case, the characteristic is gross motor function.
- Clinicians and families in our field may use a classification system to:
- DESCRIBE and CATEGORIZE a child’s functional status
- Facilitate COMMUNICATION amongst family, clinicians, and other professionals
- In some case, a classification system may be able to PREDICT future status, which then helps clinicians and families to SET suitable goals and PLAN well-targeted interventions
- Clinical Managers may use it for:
- PROGRAM MANAGEMENT/RESOURCE PLANNING
- Scientists/researchers may use it to:
- DESCRIBE the people with CP used in their study
- DEFINE eligibility criteria for a study
- STRATIFY participants by a given characteristic (place individuals in different levels of that characteristic)
- COMPARE participants in different level
What the Gross Motor Function Classification System does NOT do
The GMFCS does NOT:
- measure change over time or after interventions/treatment. This requires a different type of measurement tool called an outcome measure;
- compare gross motor function to that of “typically-developing” children. Again, it focuses on what the person with CP CAN do, not what they CANNOT do;
- assess the details of motor function. The Gross Motor Function Classification System looks at the big picture. People classified in the same level may use different strategies to complete motor tasks but still demonstrate similar levels of overall functioning.
Can the GMFCS be used as an outcome measure? NO!
- Recall WTQ! Researchers, clinicians, clinical managers need to consider their question carefully and determine the type of measurement tool(s) required to answer the question.
- A person with CP almost always stays in the same Gross Motor Function Classification System level over time, even if they have received treatment such as orthopaedic surgery. That doesn’t mean that no changes occur after these treatments. It means that the GMFCS was not designed to detect these changes. Thus, the answer to above question is NO, it cannot be used as an outcome tool. In order to track changes, we need to use a tool that was developed and validated as an outcome measure.
Should the Gross Motor Function Classification System be used outside of Cerebral Palsy?
Again, the simple answer is NO. Our recent published review6 found 118 articles in which the GMFCS was used with people who do not have CP. These included people, both children and adults, with 133 different conditions or clinical descriptions. Was it the correct tool for the job? PROBABLY NOT. The GMFCS was based on the gross motor function of individuals with CP. As such, the descriptions for the levels are specific to how people with CP move and function. People with different conditions do not move and function in the same way as individuals with CP. Therefore, they might not fit into the levels described in the GMFCS
- Here is a prime example: A study from 2003 by Bodkin et al., (7) evaluated the use of the GMFCS with 27 children with Down syndrome. They found that by the time the children were just over 2 years of age, almost all were classified in GMFCS Level I, which is not helpful if you are trying to differentiate between groups with different abilities. These findings are consistent with other studies have shown that children with Down syndrome follow a motor skill pattern different from that of children with CP. (8)
Conclusions from this review6
- The GMFCS should not be used as an outcome measure.
- The GMFCS should not be used with people who do not have CP.
- We must always keep in mind “WTQ?” Different tools are designed to carry out different jobs. Using the wrong tool will usually not help you find the correct answer to your specific questions; it may, in fact, mislead you. The wrong answer could provide unsuitable information on which to base important decisions, such as whether to go ahead with a specific treatment. The only way to determine if the measurement tool you want to use is able to answer your question is to test its ability to answer that specific question with the people for whom the question is relevant (i.e. look for evidence of validity and reliability for your question). If that testing has not been done, then that tool should not be used. This will always be the case.
- As such, there is a need for other condition-specific gross motor function classification systems, and potentially a generic classification system that could be used across different conditions.
Special thanks to Francine Buchanan and JoAnne Golt for critically reviewing this document.
- Palisano R, Rosenbaum P, Walter S, Russell D, Wood E, Galuppi B. 1997. Development and reliability of a system to classify gross motor function in children with cerebral palsy. Developmental Medicine and Child Neurology; 39: 214-23.
- Palisano RJ, Rosenbaum P, Bartlett D, Livingston MH. 2008. Content validity of the expanded and revised Gross Motor Function Classification System. Developmental Medicine and Child Neurology; 50: 744-50.
- Rosenbaum PL, Palisano RJ, Bartlett DJ, Galuppi BE, Russell DJ. 2008. Development of the Gross Motor Function Classification System for cerebral palsy. Developmental Medicine and Child Neurology; 50:249-53.
- Palisano RJ, Cameron D, Rosenbaum PL, Walter SD, Russell D. 2006. Stability of the Gross Motor Function Classification System. Developmental Medicine and Child Neurology; 48: 424-8.
- Rutz E, Tirosh O, Thamason P, Barg A, Graham KH. 2012. Stability of the Gross Motor Function Classification System after single-even multilevel surgery in children with cerebral palsy. Developmental Medicine and Child Neurology; 54: 1109-13.
- Towns M, Rosenbaum PL, Palisano RJ, Wright FV. (2017). Should the GMFCS be used outside of cerebral palsy? Developmental Medicine and Child Neurology; 60: 147-154.
- Bodkin AW, Robinson C, Perales FP. 2003. Reliability and validity of the Gross Motor Function Classification System for cerebral palsy. Pediatric Physical Therapy; 15: 247-52.
- Palisano RJ, Walter SD, Russell DJ, Rosenbaum PL, Gemus M, Galuppi BE, Cunningham L. 2001. Gross motor function of children with Down syndrome: creation of motor growth curves. Archives of Physical Medicine and Reabilitation; 82: 494-500.