Validity, Intra-Rater Reliability and Normative Data of the Neuroflexor™ Device to Measure Spasticity of the Ankle Plantar Flexors after Stroke.

Abstract

Quantification of lower limb spasticity after stroke and the differentiation of neural from passive muscle resistance remain key clinical challenges. The aim of this study was to validate the novel NeuroFlexor foot module, to assess the intrarater reliability of measurements and to identify normative cut-off values. Fifteen patients with chronic stroke with clinical history of spasticity and 18 healthy subjects were examined with the NeuroFlexor foot module at controlled velocities. Elastic, viscous and neural components of passive dorsiflexion resistance were quantified (in Newton, N). The neural component, reflecting stretch reflex mediated resistance, was validated against electromyography activity. A test-retest design with a 2-way random effects model permitted study of intra-rater reliability. Finally, data from 73 healthy subjects were used to establish cutoff values according to mean + 3 standard deviations and receiver operating characteristic curve analysis. The neural component was higher in stroke patients, increased with stretch velocity and correlated with electromyography amplitude. Reliability was high for the neural component (intraclass correlation coefficient model 2.1 (ICC2,1) ≥ 0.903) and good for the elastic component (ICC2,1 ≥ 0.898). Cutoff values were identified, and all patients with neural component above the limit presented pathological electromyography amplitude (area under the curve (AUC) = 1.00, sensitivity = 100%, specificity = 100%). The NeuroFlexor may offer a clinically feasible and non-invasive way to objectively quantify lower limb spasticity.