Abstract
Hemiparetic stroke in adulthood often results in the grouped movement pattern of the upper extremity flexion synergy thought to arise from an increased reliance on cortico-reticulospinal pathways due to a loss of lateral corticospinal projections. It is well established that the flexion synergy induces reaching constraints in individuals with adult-onset hemiplegia. The expression of the flexion synergy in individuals with brain injuries onset earlier in the lifespan is currently unknown. An early unilateral brain injury occurring prior to six months post full-term may preserve corticospinal projections which can be used for independent joint control and thus minimizing the expression of the flexion synergy. This study uses kinematics of a ballistic reaching task to evaluate the expression of the flexion synergy in individuals with pediatric hemiplegia (PH) ages six to seventeen years. Fifteen individuals with brain injuries before birth (n = 8) and around full-term (n = 7) and nine age-matched controls with no known neurological impairment completed a set of reaches in an admittance controlled robotic device. Descending drive, and the possible expression of the upper extremity flexion synergy, was modulated by increasing shoulder abduction loading. Individuals with early-onset PH achieved lower peak velocities when reaching with the paretic arm compared to controls; however, no differences in reaching distance were found between groups. Relative maintenance in reaching seen in individuals with early brain injuries highlights minimal expression of the flexion synergy. We interpret this conservation of independent control of the paretic shoulder and elbow as the use of more direct corticospinal projections instead of indirect cortico-reticulospinal pathways used in individuals with adult-onset hemiplegia.
Highlights
Hemiplegia results from a unilateral lesion to the developing or mature brain and can lead to impairments to upper limb function in the impaired or paretic arm
We found that while there was a relative maintenance in reaching distance between groups, individuals with pediatric hemiplegia (PH) achieved significantly lower peak velocities in the paretic arm compared to the non-dominant arm of the typical development (TD) group
We have shown that individuals with early lesions are minimally influenced by the particular impairment of the flexion synergy during a high effort reaching task
Summary
Hemiplegia results from a unilateral lesion to the developing (pediatric-onset) or mature (adultonset) brain and can lead to impairments to upper limb function in the impaired or paretic arm. Impairment is believed to be especially caused by the expression of the “flexion synergy” described by Brunnstrom (1970) as abnormal coupling of shoulder abduction (SABD) with shoulder extension and elbow, wrist, and finger flexion. Investigation of the flexion synergy in isometric conditions in individuals with adult-onset hemiplegia has revealed abnormal coupling between SABD and elbow, wrist, and finger flexion when measuring torques and muscle activity (Dewald et al, 1995, 2001; Beer et al, 1999; Dewald and Beer, 2001; McPherson and Dewald, 2019). The current study explores whether this expression exists in children and adolescents with PH given that corticospinal pathways are still maturing at the time of lesion (Eyre et al, 2001; Staudt, 2010)
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