The influence of passive-dynamic ankle-foot orthosis bending axis location on gait performance in individuals with lower-limb impairments

• Passive-dynamic ankle-foot orthoses with varied bending axes were studied.
• Minor differences in gait measures across bending axis locations were observed.
• Bending axis preference was strongly related to various gait measures.
• Preference and comfort are important factors in prescribing axis location.

BackgroundPassive-dynamic ankle-foot orthoses are commonly prescribed to augment impaired ankle muscle function, however their design and prescription are largely qualitative. One design includes a footplate and cuff, and flexible strut connecting the two. During gait, deflection occurs along the strut, with the greatest deflection at a central bending axis. The vertical location of the axis can affect lower extremity biomechanics. The goal of this study was to investigate the influence of bending axis location on gait performance.MethodsFor thirteen participants with unilateral ankle muscle weakness, an additive manufacturing framework was used to fabricate passive-dynamic ankle-foot orthosis struts with central and off-center bending axes. Participants walked overground while electromyographic, kinetic and kinematic data were collected for three different bending axes: proximal (high), central (middle) and distal (low), and the participants indicated their order of bending axis preference after testing. Gait measures and preference effect sizes were examined during six regions of the gait cycle.FindingsA few differences between bending axes were observed: in the first double-leg support peak plantarflexion angle, peak dorsiflexion moment and positive hip work, in the early single-leg support peak knee extension moment and positive ankle and knee work, and in the late single-leg support gastrocnemius activity and vertical ground reaction force impulse. In addition, preference was strongly related to various gait measures.InterpretationDespite the observed statistical differences, altering bending axis location did not produce large and consistent changes in gait performance. Thus, individual preference and comfort may be more important factors guiding prescription.