Impaired grip-lift synergy in children with unilateral brain lesions

Children with spastic hemiplegia have impaired dexterity in the affected ex tremity, The purpose of the present study was to investigate whether the fo rce co-ordination pattern during precision grip in 13 children between 4 an d 10 years of age with predominant unilateral brain lesions is related to m anual dexterity and to the location and size of the brain lesion. The force co-ordination pattern was investigated by means of a specially designed ob ject that monitored the isometric fingertip forces applied to the contact s urfaces during precision grip, Hand function was measured by means of neuro logical examination, functional hand-grips and dexterity, Brain lesions wer e identified by series of ultrasound and MRI scans. Normally, the fingertip forces are applied to the object in the initial phase of the lift in an in variant force co-ordination pattern (i.e. grip-lift synergy), in which the grip and load forces are initiated simultaneously and increase in parallel with unimodal force rate trajectories. A majority of children with unilater al brain lesions had not developed the force co-ordination pattern typical for their age, but produced an immature or a pathological pattern. The deve lopmental level of the grip-lift synergy was determined and quantified acco rding to criteria derived from earlier studies on normally developed childr en, There was a clear relationship between the developmental level of the g rip-lift synergy and impaired dexterity, indicating that proper development of the force co-ordination pattern is important for skilled hand function, The grip-lift synergy correlated with the total extent of lesions in the c ontralateral cortex and white matter and with lesions in the thalamus/basal ganglia, while no correlation was found for isolated cortical lesions. The results suggest that the neural circuits involved in the control of the pr ecision grip are organized in a parallel and distributed system in the hemi spheres, and that the basal ganglia are important during the formation of t hese circuits. Perinatal lesions in specific cortical motor areas may be co mpensated for by circuits elsewhere in the grip-lift motor system, while la rge lesions exclude this possibility.