Impact of ankle-foot-orthosis on frontal plane behaviors post-stroke

Abnormal within and across-joint synergistic behaviors have been reported in the lower limb post stroke. It is unknown, however, whether these impairments limit adaptive movement strategies in response to imposed kinematic constraints. In this context, the goal of this pilot study was to examine changes to three-dimensional swing phase kinematics of the paretic hip, knee, and ankle joints and pelvis induced by AFO use in subjects with chronic stroke. Overground gait analysis was performed on 9 ambulating hemiplegic subjects with and without their AFOs. Both the toeoff and peak ankle dorsiflexion angles were significantly decreased in the no AFO condition. Likewise, the peak and toeoff swing phase pelvic obliquity angles significantly increased when the AFO was removed (6.47 degrees (2.0 SD) vs. 8.16 degrees (2.8 SD), paired t-tests, p=0.03 and 0.8 degrees (3.1 SD) vs. 2.9 degrees (1.1 SD), paired t-test, p=0.02, respectively). These behaviors were consistent across subjects (7 of 9 subjects). The hip frontal plane, and hip and knee sagittal plane kinematics were unaffected by removal of the AFO. Finally, the minimum toe clearance was not affected by the removal of the AFO (1.39 cm+/-0.62 SD vs. 1.27 cm+/-0.47 SD, p>0.05). Taken together, these findings suggest that pelvic obliquity is the primary compensatory degree of freedom utilized to achieve toe clearance in response to impaired dorsiflexion in the stroke population. We propose that this degree of freedom is exploited as it is not constrained by synergistic torque coupling of the lower limb.