Madeline Singer, Toshiki Kobayahi, Lucas Lincoln, Michael Orendurff and K. Bo Foreman
Stroke patients suffering from foot drop are often prescribed ankle-foot orthoses (AFOs) to improve foot clearance during gait. However, excessive restriction of plantarflexion (PF) during the heel strike phase of gait has been shown to cause biomechanical changes at the knee joint. This pilot study aimed to determine how increasing the PF stiffness of an AFO affects knee joint kinematics and kinetics during heel strike in hemiplegic stroke patients with varying levels of active ankle range of motion. We hypothesized that increased PF resistance would cause an increase in anterior tibial rotation at heel strike with resulting increases in knee flexion angle and knee extension moment. To test this hypothesis, 5 stroke patients with foot drop were clinically evaluated, instrumented with reflective markers, and fitted with a spring modified AFO (Orthocare Innovations). A compression spring in the posterior aspect of the AFO was changed to increase the external dorsiflexion torque from 0.3 Nm/deg (Spring 1) to 2.0 Nm/deg (Spring 2). Kinematic and kinetic data were collected during walking on an instrumented treadmill (Bertec) in a motion analysis lab. Five steps with each spring were examined. Two patients exhibited an increase in knee flexion angle and knee extension moment with the stiffer spring. Clinical findings revealed that these 2 patients had minimal active PF while the other 3 patients had full active PF. From these initial results, we cautiously conclude that stroke patients with decreased active PF cannot overcome excessive PF resistance during the heel strike phase of gait, and as a result exhibit compensation strategies at the knee joint. These results will be used to create a more objective method for the prescription of AFOs in hopes to improve the long-term quality of life for stroke patients.
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