Influence of the medial offset of the proximal humerus on the glenohumeral destabilising forces during arm elevation: a numerical sensitivity study

Abstract

This study assessed the influence of the medial offset of the proximal humerus on the glenohumeral destabilising forces during arm elevation in the plane of the scapula, using the AnyBody Modeling System. The variability of the medial offset was covered using literature data (minimum, 0 mm; average, 7 mm and maximum, 14 mm). The following parameters were studied: moment arm (MA; middle deltoid), muscle activity and stability ratios. The minimum offset decreased the MA of the middle deltoid ( − 11%), increased its activation (+18%) and its superior destabilising action (+40%). The maximum offset had an opposite effect (+9%, − 30% and − 30%). The stabilising action of the rotator cuff was not affected. Varying the medial offset seems to have an influence on the destabilising action of the middle deltoid. The AnyBody simulation tool appears to be promising in establishing links between shoulder morphology and stability.

Keywords:

• proximal humerus anatomy
• musculoskeletal model
• joint reaction force
• stability ratio

Acknowledgements

This work was supported by the Fonds de recherche du Québec – Nature et technologies, and the MENTOR training grant of the Canadian Institutes of Health Research. The authors wish to thank the managers of the AnyScript Community forum for their clear and detailed answers to the numerous questions raised during the production of this paper.