A method to measure the accuracy of loads in knee-ankle-foot orthoses using conventional gait analysis, applied to persons with poliomyelitis

Objectives: To determine (1) the forces and moments passing through knee-ankle-foot orthoses (KAFOs) during walking and (2) the accuracy with which these loads can be measured using conventional gait analysis techniques. Design: Comparative case series. Setting: Rehabilitation facility with human movement laboratory (gait lab). Participants: Four patients with poliomyelitis wearing KAFOs. Interventions: KAFOs were instrumented with a load cell, and walking data were concurrently collected using conventional gait analysis. Main Outcome Measures: Load measurements and gait parameters. Results: Predominant orthotic loads (knee joint forces and moments) were composed of knee flexion moments and axial compression forces. With conventional gait analysis, peak knee joint moments were substantially underestimated compared with those directly measured using the load cell. Defining the knee axis anatomically versus at the orthotic axis, tracking it dynamically, and compensating for each patient's corrected knee flexion contracture resulted in considerable improvements in the gait lab estimates of knee joint moments. Conclusions: A practical method that directly measures moments and forces in conventional KAFOs has been applied to show that conventional gait analysis techniques substantially underestimate knee joint moments in the KAFOs of persons with poliomyelitis. Underestimation of orthotic loads could result in underdesigned orthotic components and ultimately higher incidence of component failure in clinical applications.