Forces and moments in knee–ankle–foot orthoses while walking on irregular surfaces

Abstract

Kinetic data provide important information about the mobility performance of individuals with lower limb impairments and their assistive devices; however, there is limited understanding of this in real-life environments. To evaluate the effect of real-life irregular surfaces on forces and moments in knee-ankle-foot orthoses. In this case series study, a load cell was used to measure the forces and moments at the knee joint of knee-ankle-foot orthoses of individuals with unilateral muscle weakness as a result of poliomyelitis while walking on different ground surfaces and at different speeds. Significantly higher shear forces and external peak knee flexion moments were found when walking on irregular surfaces. In individual cases, certain irregular ground conditions elicited large increases in peak flexion moments (>50%) when compared to walking on smooth level ground. Forces and moments were significantly higher at faster walking speeds. Higher external peak knee flexion moments during the stance phase suggest that greater demands for support and stability are placed on individuals and their assistive devices when negotiating real-life ground surfaces. Clinical relevance This study demonstrates that walking on irregular surfaces alters the loads placed on knee-ankle-foot orthoses and that the requirements for knee stabilization increase. This has important clinical implications on the design, prescription, and use of such devices given the structural and functional demands placed on them.