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Relationship of Strength, Weight, Age, and Function in Ambulatory Children With Cerebral Palsy
Jon R Davids1, Donna J Oeffinger, Anita M Bagley
1*Shriners Hospital for Children, Sacramento, CA †Shriners Hospital for Children, Lexington, KY ‡Shriners Hospital for Children, Springfield, MA.
Insights
Strength normalized to weight (STR-N) declines with age in children with cerebral palsy (CP), reducing their likelihood of independent ambulation. This decline occurs across functional levels, highlighting the need for interventions to support mobility.
Area of Science:
- Neurology
- Pediatrics
- Rehabilitation Medicine
Background:
- Ambulatory function in cerebral palsy (CP) typically deteriorates with age.
- This decline is linked to unfavorable changes in the strength-to-weight ratio.
Purpose of the Study:
- To prospectively analyze the changes in lower extremity muscle strength, body weight, and strength normalized to weight (STR-N) in children with CP.
- To determine the relationship between these parameters and age, and functional impairment levels.
Main Methods:
- Prospective case series of 255 individuals (8-19 years) with diplegic CP.
- Cross-sectional data analysis using linear regression to predict age-related changes in strength, weight, and STR-N.
- Cohort analyzed overall and stratified by Gross Motor Function Classification System (GMFCS) levels.
Main Results:
- Significant increases in strength (20.83 N/y) and weight (3.5 kg/y) were observed over time.
- A significant decrease in lower extremity STR-N (0.84 N/kg/y) was found in the cohort.
- The rate of STR-N decline was consistent across age groups and GMFCS levels (I-III).
Conclusions:
- STR-N decreases with age in children with CP throughout their growing years and across GMFCS levels I-III.
- Reduced STR-N is associated with a decreased likelihood of independent ambulation.
- Findings support interventions aimed at promoting ambulation in children with CP.
Background:
The natural history of ambulatory function in individuals with cerebral palsy (CP) consists of deterioration over time. This is thought to be due, in part, to the relationship between strength and weight, which is postulated to become less favorable for ambulation with age.
Methods:
The study design was prospective, case series of 255 subjects, aged 8 to 19 years, with diplegic type of CP. The data analyzed for the study were cross-sectional. Linear regression was used to predict the rate of change in lower extremity muscle strength, body weight, and strength normalized to weight (STR-N) with age. The cohort was analyzed as a whole and in groups based on functional impairment as reflected by Gross Motor Function Classification System (GMFCS) level.
Results:
Strength increased significantly over time for the entire cohort at a rate of 20.83 N/y (P=0.01). Weight increased significantly over time for the entire cohort at a rate of 3.5 kg/y (P<0.0001). Lower extremity STR-N decreased significantly over time for the entire cohort at a rate of 0.84 N/kg/y (P<0.0001). The rate of decline in STR-N (N/kg/y) was comparable among age groups of the children in the study group. There were no significant differences in the rate of decline of STR-N (N/kg/y) among GMFCS levels. There was a 90% chance of independent ambulation (GMFCS levels I and II) when STR-N was 21 N/kg (49% predicted relative to typically developing children).
Discussion:
The results of this study support the longstanding clinically based observation that STR-N decreases with age in children with CP. This decrease occurs throughout the growing years, and across GMFCS levels I to III. Independent ambulation becomes less likely as STR-N decreases. This information can be used to support the rationale, and provide guidelines, for a range of interventions designed to promote ambulation in children with CP.
