Analyse numérique des paramètres biomécaniques influençant la fonction de l’épaule atteinte d’arthropathie de rupture de coiffe

Abstract

Cuff tear arthropathy (CTA) is a shoulder pathology characterized by a massive and irreparable rotator cuff tear and an abnormal contact between the humeral head and the acromion. CTA is often associated with shoulder pseudo-paralysis. However, the fact that some patients still maintain a functional shoulder remains unexplained. The goal of the present work was to numerically assess the biomechanical parameters that influence the function of the shoulder with CTA. The specific objectives were to show the influence of: (1) a variation of the medial offset of the proximal humerus on the destabilizing forces at the intact (healthy) shoulder; (2) the elevation plane and the friction coefficient on the “mechanics of CTA” and; (3) the geometrical parameters of the humeral head on the “mechanics of CTA” in the context of an emiarthroplasty. Study #1 assessed the influence of a minimum (0 mm), average (7 mm) and maximum (14 mm) medial offset on the destabilizing glenohumeral forces (transverse to the glenoid) at the intact (healthy) shoulder. Study #2 assessed the influence of the elevation plane (frontal, scapular, sagittal) and the contact friction (coefficient of 0.15, 0.3 and 0.6) on the “mechanics of CTA” (i.e. deltoid length and force; contact forces (glenoid and acromion)). Study #3 assessed the influence of a large medial offset (17 mm) associated with an oversized humeral head hemiprosthesis (120 %) on the same “mechanics of CTA” as in study #2. Study #1 showed that the maximum medial offset (14 mm) greatly decreases the destabilizing action of the deltoid without affecting the stabilizing action of the rotator cuff. The CTA model of study #2 showed that the elevation plane influences the mechanics of CTA, but that the contact condition (friction) combined with the poor mechanics of the deltoid is more likely to lead to a poor function. Study #3 showed that the combination of a large medial offset with an oversized humeral head hemiprosthesis decreases the acromiohumeral contact force and increases the range of motion more significantly compared to a simple oversized prosthetic head. The present work highlights the potential of the AnyBody software to study the sensitivity of the human musculoskeletal system (intact and injured) to morphological parameters. This work also brings new lines of thoughts regarding biomechanical parameters that influence the function of the shoulder with CTA. Finally, this work proposes an oversized humeral hemiprosthesis with a large medial offset as an alternative CTA treatment for young patients with poor function, thus leaving more room for revision surgery.

Date	10 Jan 2013
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Nicola Hagemeister (Supervisor) & Natalia Nuño (Co-supervisor)