Stepping with an ankle foot orthosis re-examined: a mechanical perspective for clinical decision making

Background: Ankle foot orthoses are used to stabilize the ankle joint and aid toe clearance during stepping in persons after incomplete spinal cord injury. However, little is known about kinematics and kinetics of stepping with an orthosis during the transition from stance-to-swing and swing-to-stance. We intended to examine if an ankle foot orthosis impeded or facilitated optimal ankle, knee and hip joint kinematics, kinetics and spatiotemporal parameters during the transition phases of normal walking.

Methods: Fourteen healthy participants walked on a split-belt instrumented treadmill with and without a posterior leaf spring ankle foot orthosis at 1.2m/s. Three dimensional motion data and ground reaction forces were captured during 30-second trials of steady state walking.

Findings: During stance-to-swing, the orthosis significantly decreased hip extension [8.6 (5.5) to 6.7 (5.5) degrees, P=0.001], ankle plantarflexion [19.4 (5.7) to 12.0 (5.2) degrees, P<0.001] and plantarflexor power [0.18 (0.03) to 0.15 (0.03) watts/body weight, P<0.001]. During swing-to-stance, the orthosis significantly increased hip flexion [32.7 (4.7) to 35.6 (5.1) degrees, P=0.028] and ankle plantarflexion [8.4 (3.5) to 10.9 (4.7) degrees, P<0.001] and decreased loading rate [0.06 (0.01) to 0.05 (0.01) N/kg, P=0.018] and braking force [0.16 (0.02) to 0.15 (0.02) N/kg, P=0.013]. Double limb support time increased significantly with the orthosis [0.19 (0.02) to 0.22 (0.03) seconds, P<0.000].

Interpretation: An ankle foot orthosis affected joint kinematics and kinetics during the transition from stance-to-swing and vice-versa. The use of orthosis to improve transition phase kinematics and kinetics in individuals with incomplete spinal cord injury warrants assessment.