Three-dimensional assessment of finger individuation reveals finger- and joint-specific selective motor control deficits in children with cerebral palsy

Children with cerebral palsy (CP) exhibit impaired selective motor control (SMC) that contributes to poor hand function, but current clinical assessments lack the sensitivity to detect finger- and joint-specific deficits to guide rehabilitation strategies. This study aimed to determine the internal consistency and validity of an objective, instrumented assessment of selective finger control (individuation) in children with CP, and to examine its relationship to clinical measures of upper limb function. A custom-designed device recorded three-dimensional isometric forces concurrently from all five fingertips to compute a composite metric of finger SMC (Individuation Index) for each tested finger and force direction. Group differences in individuation ability were quantified using linear mixed-effect models. Relationships between individuation and clinical assessments were assessed with Spearman correlation (rs). Twenty-eight children with CP and 18 typically developing control children were included. The non-preferred arm was tested in most children with CP (n = 16), with the preferred arm tested in controls and the remaining CP cohort. Individuation Indexes demonstrated excellent internal consistency across groups (all R ≥ 0.97). Children with CP exhibited lower individuation than controls in both the preferred (Cohen’s d (d) = 0.73) and non-preferred hands, with deficits in the non-preferred hand more pronounced during finger flexion (d = 1.48), in the index finger (d = 1.52), and in those exhibiting mirror movements (d = 0.56). Exploratory analysis in children with CP tested bilaterally (n = 6) revealed finger-specific differences, with lower individuation observed in the index finger of the non-preferred hand (d = 1.36). In children with CP, higher Individuation Indexes for ab-/adduction forces in the preferred hand were related to better fine and gross manual ability (rs = 0.86 and 0.76, respectively; both p 0.05). This study provides a consistent, valid, and sensitive method to quantify finger SMC in children with CP, revealing finger-, force direction-, and hand-specific impairments that highlight aspects of dexterity not captured by clinical assessments. Quantifying finger individuation enables more precise characterization of hand dysfunction, advancing mechanistic understanding and targeted intervention design for children with CP. Trial registration Data collected as part of a larger randomized controlled trial; https://clinicaltrials.gov/ct2/show/NCT03484078 .