A novel instrument for quantifying grip activity during handwriting.

Objective: To describe and exemplify a noninvasive instrumentation system that uniquely records grip forces exerted on the barrel of the writing utensil along with typical temporal and kinematic parameters.

Design: Exploratory case series.

Setting: A tertiary care, pediatric rehabilitation hospital.

Participants: Convenience sample of 6 primary school children with spastic hemiplegic cerebral palsy (CP) with documented fine motor difficulties and 6 children with no known handwriting difficulties.

Interventions: Not applicable.

Main Outcome Measures: Grip and normal forces during handwriting.

Results: The instrumentation revealed nontrivial correlations between normal and grip forces (0.55 +/- 0.16), a temporal delay between normal and grip forces (97.7 +/- 16 ms), and a consistent grip-to-normal force ratio (4.3 +/- 1.5), across all participants. Grip force distributions agreed intuitively with qualitative observations of individual grasps of the writing utensil. Further, 5 new parameters derived from grip force measures statistically differentiated between able-bodied children and those with hemiplegic CP.

Conclusions: The proposed instrumentation provides new insight into grip and normal force coordination and has the potential to uncover discriminatory grip force characteristics between writers with and without handwriting difficulties. Further study with larger populations is required to define functional ranges for the new grip measures.