Full length article An anatomically unbiased foot template for inter-subject plantar pressure evaluation Todd C. Pataky a, *, Kerstin Bosch b , Tingting Mu c , Noe¨ l L.W. Keijsers d , Veerle Segers e , Dieter Rosenbaum b , John Y. Goulermas f a Department of Bioengineering, Shinshu University, Tokida 3-15-1 Ueda, Nagano 386-8567, Japan b Movement Analysis Lab, Orthopaedic Department, University Hospital Mu¨nster, Albert-Schweitzer-Str. 33, Mu¨nster 48149, Germany c School of Computer Science, University of Manchester, Oxford Road, Manchester M13 9PL, UK d Department of Research, Development and Education, Sint Maartenskliniek, Hengstdal 3, 6522 JV Nijmegen, The Netherlands e Department of Movement and Sport Sciences, Ghent University, Watersportlaan 2, 9000 Ghent, Belgium f Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill, Liverpool L69 3GJ, UK 1. Introduction Statistical analyses of pedobarographic images have tradition- ally consisted of discrete regional scalar extraction [1–3]. It has also been shown that, following spatial registration [4], these images can alternatively be analyzed in a continuous manner using Statistical Prametric Mapping (SPM) [5,6]. SPM takes advantage of spatial correlation to conduct statistical inference across the entire pressure field. One advantage of this approach is that anatomical meaning is implicit in the resulting statistical images, so one avoids potential problems associated with explicit labeling of broad discrete regions [6]. Although registration generally ensures homologous data analysis, pedobarographic SPM analyses have, to date, used arbitrary subjects as registration templates. This is not ideal because subject peculiarities could conceivably introduce regis- tration bias which could, in turn, affect the ultimate statistical results. The solution is to use a hypothetically average subject which, by definition of central tendency, constitutes an unbiased approach. The main purpose of the current study was to construct a pedobarographic template that: (i) embodied healthy average morphology and pressure distribution, and (ii) was minimally biased by subject peculiarities. A secondary purpose was to demonstrate how this template could be used for population- based scientific studies. 2. Methods 2.1. Dataset Pedobarographic data were collected from N = 104 healthy adult volunteers at the University of Mu¨ nster (Table 1). Subjects performed five trials of self-paced walking for both the left and Gait & Posture 33 (2011) 418–422 ARTICLE INFO Article history: Received 22 June 2010 Received in revised form 29 September 2010 Accepted 13 December 2010 Keywords: Pedobarography Foot morphology Image registration Spatial statistics Statistical parametric mapping ABSTRACT Pedobarographic images reflect the dynamic interaction between the plantar foot and supporting surfaces during gait and postural activities. Since intra-foot and inter-subject contact geometry are grossly similar, images may be spatially registered and directly compared. Previously arbitrary subjects have been selected as registration templates, but this can conceivably introduce anatomical bias. The purposes of this study were: (i) to compute an unbiased pedobarographic template from a large sample of healthy young adult subjects, and (ii) to demonstrate how the resulting template may be used for practical clinical and scientific analyses. Images were obtained from N = 104 subjects and were registered (10,712 pairs) using (i) an optimal linear scaling technique and (ii) a nonlinear, locally affine, globally smooth technique. The nonlinear technique was found to offer biomechanically non-trivial advantages over the linear technique, most likely due to non-proportional inter-subject geometry. Specifically, the nonlinear template was able to detect morphological signals in a hallux valgus sample with greater sensitivity than the linear template. Validity of the approach was confirmed by independently assessing left and right feet, through a statistical comparison of local maximal pressures, and also through examination of random subject subsets. The current template, representative of an average healthy foot, could be a valuable resource for automated clinical and scientific analyses of foot morphology and function. ß 2010 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +81 0268 21 5609. E-mail address: tpataky@shinshu-u.ac.jp (T.C. Pataky). Contents lists available at ScienceDirect Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost 0966-6362/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2010.12.015