Shoulder abduction-induced reductions in reaching work area following hemiparetic stroke: neuroscientific implications

Abstract

A stroke-related loss of corticospinal and corticobulbar pathways is postulated to result in an increased use of remaining neural substrates such as bulbospinal pathways as individuals with stroke are required to generate greater volitional shoulder abduction torques. The effect of shoulder abduction on upper extremity reaching range of motion (work area) was measured in 18 individuals with stroke using the Arm Coordination Training 3-D (ACT(3D)) device. This robotic system is capable of quantifying movement kinematics when a subject attempts to reach while simultaneously generating various levels of active shoulder abduction torque. We have provided data demonstrating an incremental increase of abnormal coupling of elbow flexion for greater levels of shoulder abduction in the paretic limb that results in a reduction in available work area as a function of active limb support. The progressive increase in the expression of abnormal shoulder/elbow coupling can be explained by a progressive reliance on the indirect cortico-bulbospinal connections that remain in individuals following a stroke-induced brain injury.

Figures

Fig. 1

ACT3D setup: orientation of the subject and the ACT3D. Changing the forearm-hand orthosis and the relative orientation of the subject to the robot allows both arms to be studied in the same setup. The line drawing shows the subject in the initial position used for location of the shoulder and configuration of the feedback

Fig. 2

Subject seated in the ACT3D system. His trunk is secured by straps and the arm is attached to the HM with the lightweight forearm-hand orthosis. He is looking at the computer monitor for visual feedback, shown in Fig. 3

Fig. 3

Example of the visual feedback a subject would receive when their left arm is being tested. In the same configuration as the subject's limb, the screen avatar shows joint movement and position with respect to the goal and the dark gray table surface. The black arc represents the longest reach they are able to make, as measured by adding the three limb segments and the light gray tracing shows the path of the ‘fingertip’ endpoint

Fig. 4

Envelope abilities during various levels of limb support in the left, paretic limb (a) of a single subject, inverted for comparison to the non-paretic limb shown in (b). Axes units are in meters, and an individual's outline is provided in the non-paretic (right) side for reference

Fig. 5

Comparison of non-paretic and paretic limb work areas, normalized to the table supported condition within the arm measured revealed a significant difference between limbs for all levels of support. Bars represent standard deviations (*P < 0.05; **P < 0.001; n = 18)

Fig. 6

Shoulder-elbow angle plot for the paretic limb of the subject shown in Fig. 4. As the percentage of active support increases, there is an overall decrease in elbow extension capabilities, specifically when the subject is flexing their shoulder at the same time (upper right portion). Both joints show a reduction in range as shoulder abduction requirements increase, with significant reductions in the direction of elbow extension and shoulder flexion

Fig. 7

Maximal joint excursions as a function of limb support, with trend-lines across abduction levels. In each graph, the non-paretic limb (shown in a dashed lighter gray) remains relatively unchanged across active limb support requirements. By contrast, the paretic limb (shown in solid black) is affected, most strikingly in the elbow extension (a) and shoulder flexion (c) degrees of freedom