Thrower’s shoulder: 3D Experimental evaluation of scapulothoracic dyskinesia by EOS imaging

Objectives: In thrower’s shoulder pathology, scapulothoracic (S) dyskinesia (D) is classified by Kibler in 3 stages. However, the clinical or radiological diagnosis of SD is difficult and not very reproducible. The objective of this study was to evaluate scapular positioning on dry bones using low-dose 3D EOS imaging. Methods: A full-scale dry-bone S model (MODEL) was created which included the 2 scapulae and the thorax. A system of wedges enables adjustment of the right scapula to simulate the 3 stages of SD (MODEL0, MODEL1, MODEL2, MODEL3). Each MODEL was imaged in 7 random positions. The following points were identified by 2 observers: C7, T12, the xiphoid process, the inferomedial angle, the coracoid and the fulcrum. 28 S positioning measurements were taken. Inter- and intra-observer reproducibility were evaluated. Results: The thoracic and scapular points of interest are easily identified except for the fulcrum. The inter- and intra-observer reproducibility of the measurements were 94% and 94% for superior translation, 90% and 87% for protraction, 96% and 96% for anterior tilt, 75% and 86% for internal rotation, and 91% and 91% for lateral rotation. The average difference between the measurements of the 2 observers was -0.1 cm for distances (-3.3; 0.5; +/- 0.5) and -0.3° for angles (-8; 13; +/- 2.8). Conclusion: Bi-planar EOS imaging allows simple reproducible measurement of S positioning on dry bone. It could be used for diagnostic evaluation and quantification of SD. Low irradiation could play a role in the therapeutic follow-up. The potential in clinical use is yet to be confirmed.