A humeral head augment device for use in a modular shoulder prosthesis. The humeral head augment device has an external bearing surface with at least one surface portion that includes a radius of curvature. The radius of curvature is configured to constrain translational movement of the implanted shoulder prosthesis when the humeral head augment device is positioned within the shoulder prosthesis. The humeral head augment device also includes a coupling mechanism designed to lock the humeral head augment device to either the stem or the humeral head, thereby ensuring proper operational positioning of the device within the shoulder prosthesis and allowing the implanted shoulder prosthesis to function in a patient suffering from rotator cuff arthropathy. A shoulder prosthesis using a humeral head augment device, a method for assembling a shoulder prosthesis and method for using a humeral head augment device in a shoulder prosthesis are also disclosed.