Unraveling the interaction between pathological upper limb synergies and compensatory trunk movements during reach-to-grasp after stroke: a cross-sectional study

Abstract

The aim of the present study was to identify how pathological limb synergies between shoulder and elbow movements interact with compensatory trunk movements during a functional movement with the paretic upper limb after stroke. 3D kinematic joint and trunk angles were measured during a reach-to-grasp movement in 46 patients with stroke and 12 healthy individuals. We used principal component analyses (PCA) to identify components representing linear relations between the degrees of freedom of the upper limb and trunk across patients with stroke and healthy participants. Using multivariate logistic regression analysis, we investigated whether component scores were related to the presence or absence of basic limb synergies as indicated by the arm section of the Fugl-Meyer motor assessment (FMA). Four and three principal components were extracted in patients with stroke and healthy individuals, respectively. Visual inspection revealed that the contribution of joint and trunk angles to each component differed substantially between groups. The presence of the flexion synergy (Shoulder Abduction and Elbow Flexion) was reflected by component 1, whereas the compensatory role of trunk movements for lack of shoulder and elbow movements was reflected by components 2 and 3 respectively. The presence or absence of basic limb synergies as determined by means of the FMA was significantly related to components 2 (p = 0.014) and 3 (p = 0.003) in patients with stroke. These significant relations indicate that PCA is a useful tool to identify clinically meaningful interactions between compensatory trunk movements and pathological synergies in the elbow and shoulder during reach-to-grasp after stroke.

Fig. 1

Determination of maximum reaching distance (see text) and task execution. Subject starts in the initial position (left). Subject reaches for the block (small black square) at the block position (middle) and places the block at the end position (right). The magnetic source is represented by the large black square. The small rectangles on the subject (left) indicate the position of the sensors. The dashed line represents the maximum reaching distance of the arm (MRD)

Fig. 2

Time series of trunk rotations during seven reach-to-grasp movements from start of reach-to-grasp to end of reach-to-grasp, obtained from a patient with stroke (left) and a healthy individual (right). The curves represent Forward Trunk Rotation (solid), Lateral Trunk Rotation (dash-dot), and Longitudinal Trunk Rotation (dashed). An offset of +20 and −20° was added to Forward Trunk Rotation and Lateral Trunk Rotation, respectively, to better distinguish the curves. The graphs indicate that trunk rotations were largest at the end of the reach-to-grasp movement

Fig. 3

Mean joint and trunk angles for healthy subjects and patients with stroke at end of reach-to-grasp. Error bars represent 1 SD. An asterisk indicates a significant difference

Fig. 4

Principal components in patients with stroke and healthy participants. Positive/negative component loadings indicate a positive/negative correlation between a variable and a component. Based on visual inspection, dominant joint angle contributors (black) were selected within each component