Measurement of functional heel pad behaviour in-shoe during gait using orthotic embedded ultrasonography

The ability to measure the functional behaviour of the plantar heel pad is clinically relevant in dystrophic or pathological heel conditions and may help to inform the design and development of interventions that attempt to restore normal function. In this study we present a novel technique which utilises orthotic heel inserts with an embedded ultrasound (US) transducer to allow the functional, dynamic behaviour of the heel pad to be measured in-shoe during gait. The aim of this study was to demonstrate feasibility of the technique, determine the reproducibility of measurements, and to compare the effects of two orthotic inserts: (i) a flat orthotic heel raise and (ii) a contoured heel cup insert on the behaviour of the heel pad during gait. Dynamic compression of the heel pads of 16 healthy participants was recorded during treadmill walking and combined with plantar pressure measurements to allow stiffness and energy disappation ratio (EDR) to be estimated. Inter-session reliability of the US measurements was found to be excellent (ICC2,1=0.94-0.95), as was inter-rater reliability (ICC2,1=0.89). Use of the heel cup insert significantly reduced the maximum compression of the heel pad (p<0.0001) as well as the overall stiffness of the pad (p<0.001). There was no change in EDR (p=0.949). In-shoe embedded US is a reliable method to establish person-specific functional geometry of plantar soft tissues. Use of a contoured heel cup reduces the compression of the mid portion of the heel pad.