The effect of an ankle-foot orthosis on tibiofemoral motion during step-up and step-down in healthy adults.

Background: Solid ankle-foot orthoses (SAFOs) are frequently prescribed in conditions such as cerebral palsy and stroke. Although gait is improved in the short term, long-term effects of limiting ankle and foot motion during functional activities on joints such as the knee have not been investigated. Our study purpose was to compare tibiofemoral (TF) motion in shoe and SAFO conditions in healthy adults to inform future studies in clinical populations.

Methods: A custom-made device using electromagnetic sensors was used to collect three-dimensional TF rotation data while 29 healthy adult participants (female participants = 19, age = 24.4 ± 4.5 years) performed step-up/step-down in shoe and SAFO conditions.

Results: In the SAFO condition during step-up, extent of motion was greater in frontal and transverse planes and less in the sagittal plane. Discrete values at 0%-10% of the cycle in sagittal, 50%-100% in frontal, and 40%-100% in transverse planes were statistically different, producing more abduction and external rotation. In the SAFO condition during step-down, extent of motion was significantly greater in the frontal and transverse planes. Discrete values were statistically different in 40%-60% of the cycle in sagittal, 0%-30% and 70%-90% in frontal, and 0%-30% and 70%-90% in transverse planes, producing more abduction and external rotation in the first half of the cycle and more adduction and internal rotation in the second half of the cycle.

Conclusions: An SAFO affects triplanar TF kinematics in healthy adults during step-up/step-down. Future investigations into ankle-foot orthosis prescription and TF motion in clinical populations will facilitate optimal ankle-foot orthosis prescription and knee function in the long term.