A SURFACE CURVATURE TECHNIQUE FOR ANALYSING SCAPULAR DYSKINESIS Jaco Verster, Dr Sudesh Sivarasu, Dr Tinashe Mutsvangwa Department of Biomedical Engineering, University of Cape Town, South Africa Dr Janine Gray 1 Sport Science Institute of South Africa (SSISA), Cape Town, South Africa ABSTRACT Scapular dyskinesis is a common occurrence in overhead athletes, i.e. athletes who participate in any sport where the upper arm and shoulder is used above the athlete’s head. However, no consensus has been reached on how to evaluate scapular dyskinesis quantitatively. This article describes the development of a measurement technique that can be used to evaluate certain key clinical parameters specific to scapular dyskinesis. The technique employs a 3D structured light computer vision approach to create a surface map of the soft-tissue across the scapula. This surface map is then analyzed using a surface curvature analysis to identify the key clinical parameters associated with scapular dyskinesis. The main advantage of this method is that it provides a marker-less 3D approach. This may aid with diagnosis and monitoring of scapular dyskinesis by allowing measurement data to be collected both before and after treatment and rehabilitation. We expect that this technique will make the monitoring of treatment effectiveness easier while contributing to diagnostic computer vision. Keywords: scapular dyskinesis, 3D structured light, computer vision, surface curvature. NOMENCLATURE  Mean surface curvature  #,% Principle curvatures IA Inferior angle MB Medial border AA Acromion angle INTRODUCTION When the shoulder is studied from a biomechanical perspective, the coordination between the scapula and the humerus plays a critical role in normal shoulder function [1]. Abnormal movement or resting position of the scapula is defined as scapular dyskinesis and it has been associated with shoulder pain [2]. The exact cause-and-effect relationship between scapular dyskinesis and specific pathologies or injury 1 Contact author: janineg@cricket.co.za mechanisms are not yet fully understood. There is, however, enough evidence to support the clinical importance of the scapula to prompt further investigation into the nature of involvement of the scapula in shoulder pain [3]. Furthermore, it has been shown that the measurement of shoulder and scapula kinematics provides relevant information for the diagnosis and treatment of clinical disorders, rehabilitation techniques, sports performance and injury prevention [4]. Clinical assessment of the scapula is, however, inherently challenging due to the three-dimensional (3D) nature of dyskinesis and the large amount of soft-tissue involvement. The surrounding muscle (both attached to and overlying the scapula) and the large amount of under-skin movement associated with the scapula makes the direct measurement of bony landmarks difficult. In clinical practice, assessment of the scapula is mostly done through visual observations (the scapular dyskinesis test [5]) and it is proposed that this is partly due to the disadvantages of the current measurement systems. 1.1 Creating a surface map of the scapula using 3D structured light An optical surface mapping 3D scanning technique, called structured light, is commonly used in computer vision applications to image the human body [6] [7]. Structured light is a stereovision 3D imaging solution where artificial texture is created on a smooth surface by projecting a light pattern onto the surface [8]. The projected light pattern, in combination with a calibrated projector-camera setup, can be used to reconstruct the target surface using optical triangulation. For the purposes of this project, off-the-shelf projector (NEC NP100) and SLR camera (Canon EOS 600D) equipment was used to develop a low cost structured light scanner. The camera-projector calibration techniques of Zhang et al. [9] was used to calibrate the equipment. To allow for single shot capture, a deBruijn color-stripe pattern was used to encode the images [8]. Single-shot capture allows for the 3D reconstruction of the 1 Copyright © 2019 ASME Proceedings of the 2019 Design of Medical Devices Conference DMD2019 April 15, 16-18, 2019, Minneapolis, MN, USA DMD2019-3275 Downloaded from http://asmedigitalcollection.asme.org/BIOMED/proceedings-pdf/DMD2019/41037/V001T07A004/5171377/v001t07a004-dmd2019-3275.pdf by guest on 04 November 2021