SpES: A new portable device for objective assessment of hypertonia in clinical practice

Spasticity is a motor disorder that affects millions around the world. It is a particular type of hypertonia characterized by the speed-dependent increase of the muscle stretch reflex, where its correct evaluation is essential for rehabilitation. The preferred method for this assessment is the Modified Ashworth Scale (MAS), a rank derived from clinical observations. Currently, few methods can quantify this disorder objectively. Tonic Stretch Reflex Threshold (TSRT) is a parameter speed-dependent obtained from electromyographic (EMG) measurements and angular signals. Therefore, the objective was to develop portable equipment for quantitative assessments of hypertonia based on TSRT. To this end, we designed an instrument composed of single-channel EMG, flexible optical goniometer, and software for the online computing of TSRT from acquired signals. The new equipment named SpES (Spasticity Evaluation System) was applied to measuring hypertonia of the biceps brachii in twenty-two participants. The experiment was performed during manual passive stretching of the affected limb at predefined speeds. The results provided by SpES presented a satisfactory coefficient of determination (0.70) and a strong correlation with MAS (0.79). In summary, while MAS depends on precise clinical observations, SpES has the TSRT quantitative method embedded for reaching an objective assessment of hypertonia in clinical practice.