ASSESMENT OF KEY PARAMETERS ON THE PERFORMANCE OF THE DELTOID MUSCLE IN REVERSE SHOULDER ARTHROPLASTY - A MODELING AND SIMULATION-BASED STUDY

Reverse shoulder arthroplasty (RSA), in which anatomic concavities of glenohumeral (GH) joint are inverted, is a popular treatment of arthritic shoulders with deficient rotator cuff. The correct positioning of the glenohumeral center of rotation and initial setting of the deltoid length (Deltoid Tension) plays an important role in the outcome of the RSA. A study of the key literature has shown that despite common use of RSA, its biomechanical characteristics during motion are not fully understood. This study investigates the influence of some of the key parameters on the intensity of the moment in a shoulder after RSA during abduction in scapular plane. The kinematics after RSA are then compared with the anatomic shoulder kinematics and differences are discussed. Mathematical models of both the anatomical and reverse shoulder (RS) were developed in MATLAB and in MSC ADAMS. The anatomical and RSA geometries were defined using measurements obtained from X-ray and magnetic resonance imaging (MRI) images of the shoulder girdle. The results show that in RSA, the intensity of the moment generated in the GH joint improves. However, this improvement does not show a constant trend and its intensity can dramatically decrease in higher GH joint abduction.