Developmental Trajectories and Reference Percentiles for the 6-Minute Walk Test for Children With Cerebral Palsy article summary
In the introduction the authors discuss how inactivity is a big problem in children with Cerebral Palsy (CP) compared to those with normal development, and those with other pediatric disabilities. Due to the large problem of inactivity in those with CP, different types of physical activity such as walking have been identified as good interventions to use during physical therapy. The 6MWT was discussed as an excellent way to both exercise tolerance and endurance in children who are normally developing and in those with CP in order to monitor change in function and as an outcome following surgery. Previous studies have compared the 6WMT distances for Gross Motor Function Classification System (GMFCS) levels 1-3. However, those studies were completed in several different countries, and had variations made to the 6 MWT. The purpose of this study was to document long term development trajectories in 6MWT distances, along with age specific reference percentiles, including how much change is expected over 1 year on the 6MWT, for GMFCS levels 1-3. The study included a total of 456 children ages 3 to 12 with GMFCS levels 1-3. Children from the study were recruited from various places in Canada and the United States. Children excluded from the study included those under 3 years old due to possible lack of comprehension, those with another medical condition that could impact the study results, and those who are unable to speak/understand English, Spanish, or French. Methods included: children participating in up to 5 sessions with a trained physical therapist or occupational therapist either in their home or in a clinic. The children in the study were in 1 of 2 protocols. One protocol included: a two-visit study where sessions occurred at the very beginning and then 12 months later. The second protocol included: a 5-visit study where visits occurred at the beginning, 6 months, 12 months, 18 months, and 24 months. Data from both protocols were put together to achieve the purpose of this study. Therapists were kept consistent between children unless the child moved, or the therapist was not available to complete the test. The GMFCS was completed by both the therapist and the child’s parents and then compared in order to determine the appropriate level. Parents were involved in this process due to the researcher’s belief that parents know their children best and know their child’s typical performance. Consensus between the parent and therapist was reached over 97% of the time. The 6MWT was completed on a 30m area that was described as flat and hard. However, it could have been completed indoors or outdoors as long as it followed the American Thoracic Society Guidelines. Children were allowed to wear orthoses if they had them and could use their assistive device if they had one as well. Standardized instructions and verbal cues were given throughout the test, and children were encouraged to keep quiet while testing in order to not slow themselves down. On to the data analysis: approximately 118 of the 1611 assessments were missing at the end of the study for a variety of reasons. Additionally, it should be noted that the 1611 comes from counting up to 3 6MWT that was completed amongst the 456 children in the study. Next, a nonlinear mixed-effects model was used to establish the longitudinal development trajectory regarding the average change in 6MWT distance with respect to age. This was done for each GMFCS level. In the model used for the data analysis, the offset age was defined as the earliest age at which a child could be measured using the 6 MWT. Reference percentiles were then created for each GMFCS level. Results from the study include: the 6MWT distance will increase as the child’s ages but will then taper off as the child reaches their functional limit relative to their GMFCS level. The functional limit for GMFCS 1 is 417m, 342m for GMFCS 2, and 180.7m for GMFCS 3. Children with level 1 GMFCS achieved 90% of their total change within the first 50 months. Children with GMFCS level 2 developed over about 69 months and did not plateau at age 12. Researchers believe this could be due to them taking longer to develop strength and balance. Researchers also stated that because GMFCS level 2 children do not plateau at age 12, they should be followed for longer to see when the plateau occurs. Children with level 3 GMFCS achieved 90% of change in about 20 months. Additionally, more change occurred in those aged 3-5 compared to those aged 5-12. This highlights the importance of early intervention. Limitations self-reported by the author include that the sample used in the study may present as a limitation, that the 2 protocols were merged for data analysis, the amount of focus of intervention was also not controlled for children in the study. Additionally, children aged 3 and up were included in the study but if the child entered the study when they were younger than 3 data was not collected until they turned 3. Also, the 6MWT was performed in different locations and weather could have been a factor for those completing the test outside. Strengths of the study include developing percentiles and reference values for the 6MWT in children with GMFCS levels 1-3 who live in Canada or the United States. By having those values therapists are able to determine how quickly a child reaches their peak based upon their level, and they can compare a 6MWT from baseline to see if the child’s endurance is improving. Outcome measures included in the study was the GMFCS and the 6MWT. The authors did repeat the 6MWT on the children but as stated beforehand specific interventions for the children were not controlled. Overall conclusions include: that the use of this data can help monitor walking capacity to inform intervention planning and to ultimately increase participation in mobility, education, and social activities in children with CP.