A Short and Distinct Time Window for Recovery of Arm Motor Control Early After Stroke Revealed With a Global Measure of Trajectory Kinematics

Abstract

Background: Studies demonstrate that most arm motor recovery occurs within three months after stroke, when measured with standard clinical scales. Improvements on these measures, however, reflect a combination of recovery in motor control, increases in strength, and acquisition of compensatory strategies.

Objective: To isolate and characterize the time course of recovery of arm motor control over the first year poststroke.

Methods: Longitudinal study of 18 participants with acute ischemic stroke. Motor control was evaluated using a global kinematic measure derived from a 2-dimensional reaching task designed to minimize the need for antigravity strength and prevent compensation. Arm impairment was evaluated with the Fugl-Meyer Assessment of the upper extremity (FMA-UE), activity limitation with the Action Research Arm Test (ARAT), and strength with biceps dynamometry. Assessments were conducted at: 1.5, 5, 14, 27, and 54 weeks poststroke.

Results: Motor control in the paretic arm improved up to week 5, with no further improvement beyond this time point. In contrast, improvements in the FMA-UE, ARAT, and biceps dynamometry continued beyond 5 weeks, with a similar magnitude of improvement between weeks 5 and 54 as the one observed between weeks 1.5 and 5.

Conclusions: Recovery after stroke plateaued much earlier for arm motor control, isolated with a global kinematic measure, compared to motor function assessed with clinical scales. This dissociation between the time courses of kinematic and clinical measures of recovery may be due to the contribution of strength improvement to the latter. Novel interventions, focused on the first month poststroke, will be required to exploit the narrower window of spontaneous recovery for motor control.

Keywords: kinematics; motor recovery; reaching; stroke; upper limb.

Figure 1

A. Experimental kinematic apparatus (modified from Przybyla et al.), and sample trajectories for B. the dominant right arm of a healthy control subject (AMD2= 3.95) and C. the paretic dominant right arm of a stroke participant (AMD2= 33.86, FMA-UE= 58).

Figure 2

Time-course of motor control (AMD2) for paretic (A.) and non-paretic (B.) arms for individual stroke participants (grey) and mean regression linear model (black) with standard error bars. The horizontal black dotted lines indicate the average AMD2 of both dominant and non-dominant arms in healthy control subjects. For both arms there was clear improvement in motor control between week 1.5 and 5. No further improvement in motor control was seen beyond week 5.

Figure 3

Severity of impairment and time-course of motor control (AMD2) for the paretic arm of all stroke participants. Participants were divided in two groups based on their motor control impairment severity (AMD2 at 5 weeks): in black, participants above the AMD2 median value (representing the more severely impaired), and in grey, participants below the AMD2 median value (representing the less impaired.) The black dotted line indicates the average AMD2 of both dominant and non-dominant arms in healthy control subjects. Although not significant, we observed some recovery of motor control beyond week 5 for subjects in the more severely impaired group.

Figure 4

Time-course of clinical scales: FMA-UE (A.), ARAT (B.), and Biceps dynamometry Z-score (C.) for individual stroke participants (grey), and mean regression linear model (black) with standard error bars. The horizontal black dotted lines in A. and B. indicate the maximum possible scores for both measures (i.e: ARAT= 57, FMA-UE=66). For all clinical measures, the biggest improvement was seen between week 1.5 and week 5. Improvement in all clinical measures continued beyond week 5.

Figure 5

Normalized time-course for all outcome variables: AMD2, ARAT, FMA-UE, and Biceps dynamometry (strength) Z-score. The horizontal gray dotted line indicates the normalized value of the recovery achieved between the first and the second visit for each measure, which is one. AMD2 plateaued at week 5, while all clinical measures continued to improve through the first year after stroke.