Effect of image resolution manipulation in rearfoot angle measurements obtained with photogrammetry

Abstract

The aim of this study was to investigate the influence of image resolution manipulation on the photogrammetric measurement of the rearfoot static angle. The study design was that of a reliability study. We evaluated 19 healthy young adults (11 females and 8 males). The photographs were taken at 1536 pixels in the greatest dimension, resized into four different resolutions (1200, 768, 600, 384 pixels) and analyzed by three equally trained examiners on a 96-pixels per inch (ppi) screen. An experienced physiotherapist marked the anatomic landmarks of rearfoot static angles on two occasions within a 1-week interval. Three different examiners had marked angles on digital pictures. The systematic error and the smallest detectable difference were calculated from the angle values between the image resolutions and times of evaluation. Different resolutions were compared by analysis of variance. Inter- and intra-examiner reliability was calculated by intra-class correlation coefficients (ICC). The rearfoot static angles obtained by the examiners in each resolution were not different (P > 0.05); however, the higher the image resolution the better the inter-examiner reliability. The intra-examiner reliability (within a 1-week interval) was considered to be unacceptable for all image resolutions (ICC range: 0.08-0.52). The whole body image of an adult with a minimum size of 768 pixels analyzed on a 96-ppi screen can provide very good inter-examiner reliability for photogrammetric measurements of rearfoot static angles (ICC range: 0.85-0.92), although the intra-examiner reliability within each resolution was not acceptable. Therefore, this method is not a proper tool for follow-up evaluations of patients within a therapeutic protocol.

Feet positioning in the semi-static postural evaluation through photogrammetry: a systematic review

“…Table 2 presents the main methodological information of included studies. Although the methodology practically differs in all studies, the feet positioning was assembled in groups and the most common were: with inferior members in parallel and separated by a previously determined distance (Barbosa, Amorin, Zandonade, & Delaprane, 2013;Belli, et al, 2009;Iunes, Cecílio, Dozza, & Almeida, 2010;Iunes et al, 2005;Milanesi et al, 2011;Pezzan, João, Ribeiro, & Manfio, 2011;Sacco et al, 2007;Sacco et al, 2012;Tavares et al, 2013); with the inferior members positioned together (Chiao Yi, Jardim, Inoue, & Pignatari, 2008;Futlanetto, Chaise, Candotti, & Loss, 2011;Furlanetto et al, 2012;Munhoz, Marquez, & Siqueira, 2005); with the individual standing in self-referred or usual posture (Fedorak, Ashworth, Marshall, & Paul, 2003;Gadotti & Biasotto-Gonzalez, 2010;Gadotti, Armijo-Olivo, Silveira, & Magee, 2013;Raine & Towmey, 1994a;Raine & Towmey, 1994b;Salazadeh et al, 2014;Yu Cho, 2007); and standardizing the individual usual posture by using the strategy of outlining the supporting base of each person to utilize as a mold for the photos (Coelho et al, 2013;Coelho et al, 2014;de Almeida et al, 2013;Dunk, Lalonde, & Callaghan, 2005;Ferreira, Duarte, Maldonado, Bersanett, & Marques, 2011;Figueiredo, Amaral, & Shimano, 2012;Glaner, Mota, Viana, & Santos, 2012;Lopes et al, 2014;Miranda, Schor, & Girão, 2009;Pachioni et al, 2011;…”

“…Another well-established pattern of foot positioning utilizes the lower limbs positioned in parallel and apart (Barbosa et al, 2013;Belli et al, 2009;Iunes et al, 2005;Iunes et al, 2010;Milanesi et al, 2011;Pezzan et al, 2011;Sacco et al, 2007;Sacco et al, 2012;Tavares et al, 2013). One example of protocol that utilizes that type of position for photogrammetry is the classical study by Kendall et al (1995) which believes that postural evaluation should be conducted with a supporting base with the individual's feet in parallel, their heels separated by a 7.5cm distance and the hind feet abducted 8º to 10º from the median line.…”