Anatomical total shoulder arthroplasty (ATSA) often requires partial or complete resection of the capsular–ligamentous apparatus. However, the mechanical role of individual glenohumeral (GH) ligaments after implantation remains unclear. Understanding which soft tissues contribute to postoperative stability is clinically relevant given the variety of surgical approaches and tissue-sparing alternatives. This thesis aims to quantify, via the implementation of musculoskeletal multibody simulations, the mechanical contribution of the GH ligaments and capsule to joint mechanics after ATSA. Three variants of a multibody model of the shoulder including ATSA were compared: (1) an original (baseline) validated ligament-free model; (2) a model retaining only the posterior capsule (a typical outcome of the deltopectoral approach); (3) a model including the principal GH ligaments together with the posterior capsule.