To quantify the stiffness of the flexor muscles of the elbow in spastic patients using REA plan, a robotic device used in rehabilitation that can mobilize the patient's upper limb in a horizontal plane.

Twelve chronic stroke patients with hemiplegia were recruited. Spasticity of the elbow flexor muscles was assessed with Modified Ashworth Scale (MAS). Their scores were greater than 1.

Patients received an anaesthetic block of the musculo-cutaneous nerve, to reduce the spasticity of the elbow flexor muscles. Each patient was assessed before and after the injection of the anaesthetic block and a third time the next day. During each session, stiffness was measured with the REA plan. The robot passively mobilized the patient's upper limb at various speeds (10, 20, 30, 40 and 50cm/s) in a back-and-forth trajectory (30cm). For each speed condition, ten movements were performed. We recorded the force required to passively mobilize the patient's upper limb. For the ten extension movements, the strength peaks (SP) were computed and averaged.

The results showed that the SP was significantly higher in the impaired upper limb than in the unaffected arm (p<0,001), and increased proportionally with the speed condition (p<0,001). For the anaesthetic effect, the results showed that the SP decreased just after the injection at 40 and 50cm/s and increased until the initial values the next day (p<0,05). Finally, the SP results showed an excellent correlation with the MAS, for each speed condition greater than 20cm/s (r>0,6). These last results suggested that the SP reflected the spasticity of the elbow flexor muscles.

This study develops and validates a protocol to quantify the stiffness of the flexor muscles of the elbow, using the robot REA plan. This protocol, integrated to the REAplan, must be compared to other quantitative measures of spasticity in the future, and could be used to assess the effect of spasticity treatments (e.g. botulinum toxin).