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.

Relationships between static foot alignment and dynamic plantar loads in runners with acute and chronic stages of plantar fasciitis: a cross-sectional study

“…To evaluate the alignment of the rearfoot in the posterior view of the frontal plane, the runners stood over a 45 cm platform, keeping their feet 7.5 cm apart. With a dermatographic pen and 9 mm white markers, the following anatomical points were identified on the inferoposterior regions of both legs: 1) the posterior calcaneal tuberosity; 2) the second point above the center of the calcaneus; and 3) the lower third of the leg 13 , 34 , 35 ( Figure 1 ). The center of each marker in the medial-lateral axis was obtained with a digital caliper that was used to measure the distances between the two symmetrically opposing sides with a ruler 13 .…”

Influência da posição do marcador maleolar sobre os parâmetros posturais no plano sagital

“…The points were marked with white spherical styrofoam markers, with diameter of 1 cm in the tragus and 1.5 cm in the other points of interest, as determined by DIPA © protocol. Two images were obtained in sequential moments, only modifying the position of the malleolar reference marker: (1) in the center of the lateral malleolus ( Figure 2A) and (2) in front of the lateral malleolus ( Figure 2B). These images were used for comparison by the statistical procedures proposed in this study.…”

“…Photogrammetry is a postural assessment tool that provides quantitative data on individual posture 1,2 . The use of the tool follows a protocol of use that foresees the organization of the room, marking of anatomical reference points, standardization of the positioning of the volunteer to be photographed, and standardization of the equipment for capturing and processing images 3,4 .…”

Body surface posture evaluation: construction, validation and protocol of the SPGAP system (Posture evaluation rotating platform system)

“…The posture evaluation instruments most cited in the literature are: posture evaluation through observation [1–3], X-ray examination [4, 5], flexible ruler [6–8], photography, film [9–11] and scanner [12, 13]. …”

“…Photography or filming are low cost methods which are easy and quick to use [10], but they require several methodological steps such as the choice of environment, camera position, resolution of the image captured, and the use of anatomical markers [10, 11] to standardize the photos/films and prevent or reduce distortions and measurement errors. Moreover, there are some limitations inherent to the instruments, such as the analytical variations resulting from the choice of an image that does not correspond exactly to the anatomic plane under evaluation [9], which is called parallax. Since photography provides a two-dimensional image, only the part of the body that is in focus has true measurements, while the other parts might have their dimensions distorted by the effect of parallax [14].…”