Reference curves for the Gross Motor Function Measure: percentiles for clinical description and tracking over time among children with cerebral palsy

Abstract

Background and purpose: Physical therapists frequently use the 66-item Gross Motor Function Measure (GMFM-66) with the Gross Motor Function Classification System (GMFCS) to examine gross motor function in children with cerebral palsy (CP). Until now, reference percentiles for this measure were not available. The aim of this study was to improve the clinical utility of this gross motor measure by developing cross-sectional reference percentiles for the GMFM-66 within levels of the GMFCS.

Subjects and methods: A total of 1,940 motor measurements from 650 children with CP were used to develop percentiles. These observations were taken from a subsample, stratified by age and GMFCS, of those in a longitudinal cohort study reported in 2002. A standard LMS (skewness-median-coefficient of variation) method was used to develop cross-sectional reference percentiles.

Results: Reference curves were created for the GMFM-66 by age and GMFCS level, plotted at the 3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97th percentiles. The variability of change in children's percentiles over a 1-year interval also was investigated.

Discussion and conclusion: The reference percentiles extend the clinical utility of the GMFM-66 and GMFCS by providing for appropriate normative interpretation of GMFM-66 scores within GMFCS levels. When interpreting change in percentiles over time, therapists must carefully consider the large variability in change that is typical among children with CP. The use of percentiles should be supplemented by interpretation of the raw scores to understand change in function as well as relative standing.

Figure 1.

Gross motor development curves representing average development predicted by the Gross Motor Classification System. The diamonds on the vertical axis identify 4 items of the 66-item Gross Motor Function Measure (GMFM-66) that predict when children are expected to have a 50% chance of completing that item successfully. The GMFM-66 item 21 (diamond A) assesses whether a child can lift and maintain his or her head in a vertical position with trunk support by a therapist while sitting, item 24 (diamond B) assesses whether a child can maintain a sitting position on a mat without support from his or her arms for 3 seconds, item 69 (diamond C) measures a child's ability to walk forward 10 steps without support, and item 87 (diamond D) assesses the task of walking down 4 steps by alternating feet with arms free. Reprinted with permission from Rosenbaum PL, Walter SD, Hanna SE, et al. Prognosis for gross motor function in cerebral palsy: creation of motor development curves. JAMA. 2002;288:1357–1363. Copyright 2002, American Medical Association. All rights reserved.

Figure 2.

Gross Motor Function Classification System level I percentiles. GMFM-66=66-item Gross Motor Function Measure. Figure 2 may not be used or reproduced without written permission from the authors.

Figure 3.

Gross Motor Function Classification System level II percentiles. GMFM-66=66-item Gross Motor Function Measure. Figure 3 may not be used or reproduced without written permission from the authors.

Figure 4.

Gross Motor Function Classification System level III percentiles. GMFM-66=66-item Gross Motor Function Measure. Figure 4 may not be used or reproduced without written permission from the authors.

Figure 5.

Gross Motor Function Classification System level IV percentiles. GMFM-66=66-item Gross Motor Function Measure. Figure 5 may not be used or reproduced without written permission from the authors.

Figure 6.

Gross Motor Function Classification System level V percentiles. GMFM-66=66-item Gross Motor Function Measure. Figure 6 may not be used or reproduced without written permission from the authors.