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Quantitative measurement of spasticity in children with cerebral palsy
R Price1, K F Bjornson, J F Lehmann
1Department of Rehabilitation Medicine, University of Washington School of Medicine, Seattle 98195.
Insights
Children with spastic diplegia exhibit altered ankle-joint stiffness compared to typically developing children. A new method accurately detects spasticity by analyzing stiffness variations across frequencies.
Area of Science:
- Biomechanics
- Neuroscience
- Pediatrics
Background:
- Spastic diplegia is a common motor disorder in children, characterized by increased muscle tone and stiffness.
- Quantifying spasticity accurately is crucial for effective treatment and management.
- Existing methods for assessing passive stiffness may have limitations, including age dependency and the need for invasive procedures.
Purpose of the Study:
- To quantify ankle-joint passive stiffness in children with spastic diplegia across a range of frequencies.
- To differentiate spasticity from normal age-related changes in stiffness.
- To develop a modified stiffness measure that is less dependent on age and more sensitive to spasticity.
Main Methods:
- Sinusoidal displacement of the foot at frequencies from 3 to 12 Hz was used to measure ankle-joint stiffness.
- Stiffness was decomposed into elastic and viscous components.
- 'Path length' was calculated to represent stiffness variation across frequencies.
- A modified path-length measure was developed to minimize age dependency.
Main Results:
- Children with spastic diplegia showed significantly different 'path lengths' compared to unaffected children.
- An age-dependent effect on 'path length' was observed between unaffected children and adults.
- The modified path-length measure effectively detected spasticity while reducing age-related variability.
- Unaffected adults exhibited higher elastic stiffness, viscosity, and friction than unaffected children.
Conclusions:
- The 'path length' measure is a sensitive indicator of altered ankle-joint stiffness in spastic diplegia.
- A modified path-length approach offers a more robust and age-independent method for detecting spasticity.
- Understanding passive stiffness properties is vital for characterizing neurological motor disorders in children.
Abstract:
Spasticity was quantified in nine children with spastic diplegia, using a sinusoidal displacement of the foot at frequencies from 3 to 12Hz. Ankle-joint stiffness was separated into elastic (energy-storing) and viscous (energy-dissipating) components. 'Path length' was used to represent the variation in stiffness over this frequency range. Compared with 11 unaffected children, a significant difference in path lengths was demonstrated for the children with spasticity. An age-dependent effect was demonstrated when path lengths of unaffected children were compared with those of 10 unaffected adults. A modified path-length measure is proposed which minimizes age dependency, yet enables detection of spasticity. Passive stiffness properties of unaffected adults showed higher elastic stiffness, viscosity and friction than unaffected children. A method was developed to evade the need for temporary nerve blocks to calculate inerital properties of the foot in persons with spasticity.