In vivo glenohumeral translation under anterior loading in an open-MRI set-up.

The evaluation of the glenohumeral joint laxity requires the estimate of displacements of the humeral head centre (HHC) with respect to the glenoid. To the authors׳ knowledge, several studies have been conducted to estimate HHC translations in vivo but data under anterior loading conditions has not been collected yet. Aim of this study was to develop a non-invasive experimental methodology based on magnetic resonance (MR) imaging for the in vivo evaluation of the HHC translations due to an anteriorly directed force. Fourteen asymptomatic shoulders were acquired using a horizontal open MR scanner with the subjects in the supine position both at 15° and 90° of arm abduction with and without an anterior force of 20N applied at the HHC level. When no load was applied, from 15° to 90° of arm abduction, the HHC moved, anteriorly (1.5±1.3mm) and superiorly (1.8±1.3mm) while smaller displacements were observed medio-laterally (0.4±0.7mm). Under the application of the anterior force the 3D displacement of the HHC with respect to the glenoid was 1.6±1.2mm and 1.3 ±0.7mm, respectively at 15° and 90° of arm abduction. The level of precision associated to the GHJ translation was less than 0.33mm along all directions i.e. one order of magnitude smaller than the relevant translations. In conclusion, the MRI-based methodology allowed for the analysis of HHC displacements under conditions of anterior loads within an acceptable level of reliability.