Objective: Although children with cerebral palsy display large developmental differences in hand function from that of typically developing children by the age of 6 to 10 years, little is known about the developmental processes underlying hand function during subsequent development. In this study we investigated the development of manual dexterity in a timed motor task, the timing and amplitude of fingertip-force application during a precision grasping task, and the relationship between changes in these measures. We applied highly quantitative analytical approaches to determine if the fingertip-force application pattern and trial-to-trial variation of fingertip-force application change during development.
Methods: Twelve subjects with cerebral palsy (aged 6-8 years) participated in the first data-collection session conducted between 1989 and 1990. Ten of these subjects (5 with hemiplegia and 5 with diplegia, aged 19-21 years) returned between 2002 and 2003. Manual dexterity was measured by using timed tasks of the Jebsen-Taylor test of hand function. Subjects also lifted an object instrumented with force transducers while we measured the temporal coordination of fingertip coordination and the path ratio between the grip and vertical load-force trajectory (straightness). We used generalized procrustes analysis to determine if there were changes in shape of the force trajectory and intertrial variability.
Results: The Jebsen-Taylor test times decreased 45% from the first to the second data session. The overall time to complete the grip-lift task decreased 22%, mainly because of a faster transition from grasp to lift. The grip-force/load-force path ratios decreased from 1.7 to 1.35 (1 = straight line). Generalized procrustes analysis indicated a change in the shape and a decrease in variability in shape of the force-ratio path.
Conclusions: Our results demonstrate that the efficiency in grasping had developed during a 13-year period for this small group of participants with cerebral palsy, which suggests that improvement in hand function occurs over a longer time frame than commonly would be expected.