Neuro-rehabilitation robot-assisted assessments of synergy patterns of forearm, elbow and shoulder joints in chronic stroke patients

BackgroundAbnormal synergy is one of the major motor deficits in stroke patients. Abnormal muscle synergies, in conjunction with weakness and spasticity, interfere with voluntary movements and restrict the range of motion. This study aimed to quantify abnormal synergies in the affected upper limbs of chronic stroke patients by using a neuro-rehabilitation robot.MethodsTwelve chronic stroke patients and eight age-matched control subjects were recruited to perform rectilinear tracking movements in four horizontal directions (back–forth, two oblique directions at 45°, and right–left). Kinematic, kinetic and electromyogram data were recorded and used to develop two biomechanical indices and one electromyogram assessment index based on principal component analysis.FindingsSignificant differences between upper limbs of control subjects and the affected side of stroke patients were observed in all three assessment indices. Higher correlation between the elbow joint angle and the forearm pronation/supination torque, higher variation of the forearm torque, and abnormal co-contraction of the elbow and shoulder muscles were observed in the affected limbs of stroke patients. The difference was more prominent in the right–left direction and the oblique direction contra-proximal to ipsi-distal.InterpretationThe proposed assessment indices could be employed to quantify the abnormal synergies in stroke patients. Rectilinear tracking along the right–left direction and the oblique direction of contra-proximal to ipsi-distal is more suitable for assessing abnormal synergies.