Figure 3.

Modular reverse shoulder prosthesis. If both metaphyseal parts are at the same level, conversion leads to 23 mm of distalization and medializes the center of rotation by 19 mm (left). This corresponds to the worst-case scenario if the reverse metaphyseal element was placed most distally during the primary implantation of hemiarthroplasty (middle). The maximum lengthening of the conversion is 38 mm by choosing a 42 mm glenosphere and an offset of 3 mm (right). The length of the anatomic and the reverse prosthesis can be adjusted by 10 mm to reduce distalization. The center of rotation is medialized between 19 mm and 21 mm.