Biomechanical analysis of a reverse Total Shoulder Arthroplasty

Reverse Total Shoulder Arthroplasty (rTSA) is currently one of the main surgical options adopted in cases of severe rotator cuff impairment, although its biomechanical implications are not yet fully understood. In particular, fractures of the acromion and scapular spine in patients undergoing rTSA represent one of the major complications, with an estimated incidence ranging from 1% to 7%. However, no study has so far explored in depth the possible biomechanical explanations for this phenomenon. The aim of this study is to analyse the loading conditions to which the scapula is subjected in the presence of a reverse prosthesis and the resulting strain state, by integrating musculoskeletal modelling techniques with finite element (FE) analysis. Muscle and joint reaction forces during abduction and flexion movements were estimated using an OpenSim model developed from open access experimental data and subsequently applied as boundary conditions in an FE model developed in Ansys to assess the distribution of stresses and strains within the scapula. A comparison was then carried out with the results obtained by simulating the same movements in the healthy contralateral limb. The results show an increase in stresses in the scapular spine of the prosthetic shoulder in both simulated movements, in agreement with clinical evidence. The study provides a biomechanical analysis that highlights the main factors influencing the risk of scapular fracture and defines an initial computational workflow that may be further extended and optimised in the future to support medical decision making in shoulder arthroplasty, with a view to patient specific personalisation.