Modular ankle robotics training in early subacute stroke: a randomized controlled pilot study

Abstract

BACKGROUND. Modular lower extremity robotics may offer a valuable avenue for restoring neuromotor control after hemiparetic stroke. Prior studies show that visually guided and visually evoked practice with an ankle robot (anklebot) improves paretic ankle motor control that translates into improved overground walking.

Objective: To assess the feasibility and efficacy of daily anklebot training during early subacute hospitalization poststroke.

Methods: Thirty-four inpatients from a stroke unit were randomly assigned to anklebot (n = 18) or passive manual stretching (n = 16) treatments. All suffered a first stroke with residual hemiparesis (ankle manual muscle test grade 1/5 to 4/5), and at least trace muscle activation in plantar- or dorsiflexion. Anklebot training employed an "assist-as-needed" approach during >200 volitional targeted paretic ankle movements, with difficulty adjusted to active range of motion and success rate. Stretching included >200 daily mobilizations in these same ranges. All sessions lasted 1 hour and assessments were not blinded.

Results: Both groups walked faster at discharge; however, the robot group improved more in percentage change of temporal symmetry (P = .032) and also of step length symmetry (P = .038), with longer nonparetic step lengths in the robot (133%) versus stretching (31%) groups. Paretic ankle control improved in the robot group, with increased peak (P ≤ .001) and mean (P ≤ .01) angular speeds, and increased movement smoothness (P ≤ .01). There were no adverse events.

Conclusion: Though limited by small sample size and restricted entry criteria, our findings suggest that modular lower extremity robotics during early subacute hospitalization is well tolerated and improves ankle motor control and gait patterning.

Keywords: ankle motor control; ankle robot; gait; rehabilitation robotics; subacute stroke.

Conflict of interest statement

Declaration of Conflicting Interests

Dr. H. I. Krebs is a co-inventor in the MIT patents for the robotic devices. He holds equity positions in Interactive Motion Technologies, Inc., the company that manufactures this type of technology under license to MIT.

© The Author(s) 2014.

Figures

Figure 1

Training protocol: A. Subject in a seated position for anklebot assessments and training in robotics suite; B. Visual display for dorsi-plantarflexion (top panel) and inversion-eversion (lower panel) formats of the “racer game” used for anklebot training. Arrows are added to denote movement direction of the approaching gates; C. Subject in a seated position for manual passive stretching in a separate clinic.

Figure 2

Effect of intervention on gait function and ankle targeting: A. Percent change for step time and step length symmetry measured as ratios of paretic-to-nonparetic sides. Decreases in percent change (Δ%) reflect shifts toward greater interlimb symmetry. P = paretic; NP = nonparetic; B. Examples of movement traces from an exemplar patient in the robot (solid black) and the stretching (solid gray) groups without anklebot assistance. Top panels show the changes in dorsiflexion (DF) movement smoothness before (left-Pre) and after (right-Post) the respective interventions. Lower panels show similar changes in plantarflexion (PF). Note that the initial ankle positions (at 0 sec) are influenced by the location of the preceding target. The movement traces also illustrate time-to-target i.e., velocity differences (steeper slope = faster movements) and improved ranges of motion for both groups over the course of hospitalization, although more pronounced for the robot trainee whose data is shown (note scale differences on y-axes Pre-Post in both DF and PF).