An Investigation of the Ground Contact Point and Sagittal Plane Displacement of Energy Storage and Return (ESR) Composite Lower-Limb Prosthetic Feet during Running
Start date: 22 June 2015
Journal: Abstract Book - ISPO World Congress 2015
Background: Energy storage and return (ESR) feet are designed for active amputees . Their design appears to be carried out on a trial and error basis . It has also been recognised there is little compelling scientific evidence to guide the clinical prescription of ESRs .
Aim: The aim of this study is to provide insight into the dynamic behaviour of ESR prosthetic feet by investigating the effect of increased velocity on the ground contact point and foot displacement.
Method: Sagittal plane displacement (utilising a displacement sensor attached between the proximal and distal end of the foot) and ground contact point (utilising a linear array of four piezo-electric ground force sensors on the metatarsal region) were recorded from an Ossur Flex-Run ESR foot attached to a highly active unilateral transtibial amputee while carrying out a series of running trials. The data collected was analysed to provide information on and relationships between: stride cadence; ground contact time; swing phase time; timing and amplitude of maximum displacement; progression of the ground contact point.
Results: The figure shows the average sagittal plane displacement from ten full strides of the Flex-Run foot while the amputee ran at velocities of 8kmh-1, 13kmh-1 and 18kmh-1 on a treadmill. These results show that maximum deflection of the foot increased minimally as the running velocity increased from 8 and 18kmh-1. In addition, ground contact time (280ms@8kmh vs. 180ms@18kmh) and stride time (750ms@8kmh vs. 560ms@18kmh) were found to decrease. An increase of force at the posterior sensor was found as the running velocity increased; indicating that the ground contact point of the foot progressed towards the rear of the foot at increased velocity.
Discussion & Conclusion: Previous studies have assumed that a prosthetic foot and amputee forms a spring/mass system and therefore the ground contact duration at different running velocities should be comparable. This research concludes that ground contact duration decreases at increased velocity. This has been found to be due to the measured shift in ground contact point rearwards along the metatarsal region at heel-strike stiffening the foot spring rate, resulting in a shorter stride duration. Further research is now needed to generalise the relationship between the key variables to provide quantitative data to inform ESR foot prescription. References :  Kobayashi, T. et al.; 2014; Clin. Biomech.
 Strike, S. et al.; 2000; Proc. Inst. Mech. Eng. H J. Eng.  Hafner, B. et al.; 2011; J. Rehabil. Res. Dev.