*2.1. Surgical Procedure*

The SMR metal baseplate has a central peg and two screws, and the SMR long stem is an inlay design with a 150◦ neck-shaft angle. The SMR Reverse HP has a 40- or 44-mm diameter to improve ROM and it is characterized by an inversion of the materials with the aim to reduce polyethylene debris and, by a smart design (inferior sphere extension and superior narrowing), to facilitate the implantation and improving range of motion. It is made of a highly cross-linked PE (X-UHMWPE) and is coupled with CoCrMo liners. The glenoid implant provides intrinsic lateralization of the center of rotation of 5.2 mm. The glenosphere also presents a 4mm eccentricity option, but it is not utilized in primary cases at our institution. The humeral stem is implanted with 0◦ of retroversion using a forearm ancillary guide. A 40 mm glenosphere was used in 39 cases and a 44 mm glenopshere in 10 cases.

All the patients received both a general anesthetic and an interscalene block. The operation was performed in beach chair position, through a deltopectoral approach. The SMR RSA (LimaCorporate S.p.A, 33038 Villanova di San Daniele del Friuli, Udine, Italy) with the HP glenosphere was implanted in all the cases (Figure 2).

**Figure 2.** SMR reverse HP glenosphere (LimaCorporate S.p.A, 33038 Villanova di San Daniele del Friuli, Udine, Italy).

#### *2.2. Clinical and Radiological Evaluation*

Clinical evaluation performed pre- and post-operatively included the Constant–Murley score (CS) [20], the Subjective Shoulder Value (SSV) [21], the American Shoulder and Elbow Surgeon (ASES) score [22], the visual analogue scale (VAS) for pain and the range of motion (ROM) in term of active anterior elevation (AE), active external rotation (ER) in position 1, and active internal rotation (IR) (Constant-Murley subcategory). All complications and reoperation were recorded.

At last follow-up, radiographical evaluation was performed on the true anteroposterior projection on the glenohumeral joint line plane, with the humerus in neutral, external, and internal rotation. All the images were evaluated by two senior orthopedic residents trained in shoulder surgery. No attempt was made to determine the reliability of the observations, and when differences in assessments were noted, the observers reached a consensus. The positioning of the glenoid implant and the presence of radiolucent lines (RLL) were evaluated according to the classification system previously described for this baseplate in the anatomic prosthesis [23]. Loosening was considered to be present if the glenoid

component had progressively migrated, as demonstrated by shift, tilt, or subsidence, or if complete radiolucency ≥ 2 mm was present in each zone [24]. On the humeral side, humeral RLL and loosening and partial or total greater tuberosity (GT) resorption were evaluated according to Melis et al. [24]. Inferior scapular notching was graded according to the classification system of Sirveaux et al. [6]. Pillar spurs and ossification, either individually or together, in the scapular-humeral space were recorded. According to the position of the inferior margin of the metallic baseplate in relation to the inferior border of the glenoid, the baseplate was evaluated to be high (inferior margin higher than inferior glenoid border) or low (inferior margin flush or lower than inferior glenoid border). Baseplate inclination was measured as the angle between the baseplate plane (line passing through the inferior e superior margin of the baseplate) and the supraspinatus fossa [16].
