Étude statique du deltoïde moyen par IRM

Abstract

The shoulder function can be affected differently in case of rotator cuff tears. The complete knowledge of such pathology is still unknown (Hansen et al., 2008). The goal of this study was to evaluate the deltoid function by calculating a ratio of coaptation/elevation forces during the initial stage of the abduction movement. The ratio was compared to the Constant (Constant et Murley, 1987) and quickDASH (IWH, 2006) scores. Furthermore, an alternative, less time-consuming and therefore clinically feasible method has been developed. MRIs (3 mm thick joined and non-overlapping) were used to build a 3D musculoskeletal model of the shoulder complex. The scapulohumeral joint was mechanically represented as a pulley system. The coaptation/elevation forces ratios of the middle deltoid were calculated as the ratio between the coaptation force of the deltoid to the glenoid surface and the elevation force of the deltoid to the humerus. The relationship between these ratios and the shoulder functionality estimated by the quickDASH (IWH, 2006) and Constant (Constant et Murley, 1987) questionnaires was studied. Finally, an alternative method was proposed. This method allows the ratio calculation directly on the MRIs without reconstructing the structures in 3D. Eleven shoulders with rotator cuff tears were reconstructed and ratios calculated. The ratios ranged from 0,35 to 0,55 (0,47 ± 0,08), the quickDASH scores from 22,5 to 80,0 (47,6 ± 14,2), and the Constant scores from 31,01 to 75,43 (56,55 ± 11,99). The alternative method was tested on 1 subject: it appears less time-consuming than the original method and is easy to apply. The ratios proved some contribution by the middle deltoid on stabilizing the scapulohumeral joint. Nevertheless, the middle deltoid globally acts as an elevator of the humerus (ratios inferiors to one). An important contribution of the anterior fibers of the middle deltoid to the scapulohumeral stability has been demonstrated. This result shows the way to new therapies. The coaptation/elevation forces ratio could predict the shoulder functionality if a correlation study is carried out with more patients. Ultimately, the alternative method allows the ratio calculation directly on MRIs: the ratio values are comparable to the initial method. Therefore, further development of that method could result in an index of interest for clinical use.

Date	7 Aug 2012
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Nicola Hagemeister (Supervisor) & Fabien Billuart (Co-supervisor)