OBJECTIVE: To study the influence of the shape of the prosthetic humeral head on shoulder biomechanics and then to evaluate the benefits of an anatomical reconstruction of the humeral head after shoulder arthroplasty. DESIGN: A 3D numerical model of a healthy shoulder was reconstructed. The model included the proximal humerus, the scapula and, for stability purposes, the subscapularis, infraspinatus and supraspinatus rotator cuff muscles. BACKGROUND: Shoulder prostheses used nowadays, called third generation, allow for a better adaptation of the implant to the anatomy of the proximal humerus than previously used implants. However, no biomechanical study has shown the benefits of this anatomical reconstruction of the humeral head. METHODS: The model was used to compare the biomechanics of a shoulder without implant with the biomechanics of the same shoulder after humeral hemiarthroplasty. Two humeral components were tested: a second-generation prosthesis and an implant with an anatomically reconstructed humeral head. RESULTS: The anatomical reconstruction of the humeral head restored the physiological motions and limited eccentric loading of the glenoid. Conversely, the second-generation implant produced contact forces in the superior extremity of the glenoid surface leading to bone stresses up to 8 times higher than for the intact shoulder. CONCLUSIONS: This analysis provided insights into the mechanical effects of different reconstructions of the humeral head and highlighted the advantages of anatomical reconstructions of the humeral head during shoulder arthroplasty.