Measurement of functional heel pad behaviour in-shoe during gait using orthotic embedded ultrasonography Scott Telfer *, James Woodburn, Deborah E. Turner Institute for Applied Health Research, School of Health and Life Sciences, Glasgow Caledonian University, UK 1. Introduction The bony prominences at the plantar surface of the foot are covered by anatomical structures which protect against the high loads generated during activities of daily living and recreational pursuits. These structures are made up of small chambers of fibrous connective tissue containing columns of fat which vary in both size and orientation depending on their location relative to the bone [1]. A number of previous reports have suggested changes to the mechanical properties of these cushioning structures may be associated with conditions such as plantar heel pain [2–4], type 2 diabetes [5,6], and with ageing in general [7]. In this article we focus on the bulk properties of the soft tissue at the plantar surface of the calcaneus, commonly referred to as the heel pad [8]. Previous in vivo studies have incorporated radiographic methods to image the heel pad during gait [4,9,10], however exposure of the subject to ionising radiation may limit the clinical and research utility of this approach. Ultrasonography (US) has been suggested as an alternative imaging modality, and has been demonstrated to be reliable and to give comparable measurements of heel pad thickness to those obtained using radiographic imaging during static loaded and unloaded condi- tions [11]. To estimate the mechanical properties of plantar tissues, investigators have used US transducers combined with load cells to simultaneously measure tissue deformation and the force applied, either as indentors [6,7,12] or embedded in the floor [13]. These quasi static approaches have the limitation that they may not reflect the dynamic properties of the foot during gait [14] or are limited to a single, initial step. Neither approach can be used in combination with footwear. Orthotic devices such as heel cups or foot orthoses are regularly prescribed as conservative interventions when plantar heel pain is present [15] although it should be noted that evidence for their efficacy is limited [16]. The mode-of action of these devices is unclear, and proposed mechanisms include redistribution of pressure to reduce peak forces or prevention of lateral displace- ment of the tissue around the bony prominence to reduce compression and provide greater protection under load. State of the art computer aided design and manufacturing technologies now present the opportunity to embed sensors within orthotic structures to monitor physiological and biomechanical properties of the foot during gait [17]. Gait & Posture 39 (2014) 328–332 A R T I C L E I N F O Article history: Received 11 June 2013 Received in revised form 24 July 2013 Accepted 28 July 2013 Keywords: Foot Heel Orthotic shoe inserts Ultrasonography A B S T R A C T 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 (ICC 2,1 = 0.94–0.95), as was inter-rater reliability (ICC 2,1 = 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. ß 2013 Elsevier B.V. All rights reserved. * Corresponding author at: Institute for Applied Health Research, School of Health and Life Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow G4 0BA, UK. Tel.: +44 0141 331 8475. E-mail addresses: scott.telfer@gcu.ac.uk, scott.telfer@gmail.com (S. Telfer). Contents lists available at ScienceDirect Gait & Posture jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/g aitp os t 0966-6362/$ – see front matter ß 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gaitpost.2013.07.118