Background: Glenoid component loosening remains a challenge in anatomic total shoulder arthroplasty (aTSA). The aims of this study were to evaluate complications, implant survival, and revision rates in patients with primary and secondary osteoarthritis (OA) undergoing stemless aTSA using the Arthrex Eclipse humeral implant with a cemented pegged all-polyethylene glenoid component and to identify risk factors leading to revision. Methods: Of 211 patients who underwent primary stemless aTSA (using the Eclipse humeral component with a cemented pegged all-polyethylene glenoid) with prospectively documented data in a local registry, 197 were evaluated, grouped by OA pathology (primary OA, 153 patients; secondary OA, 44 patients). Demographic and functional data (e.g., age, sex, shoulder function) and the cause of OA were documented preoperatively in both groups. Comparative analyses were conducted to assess complications and implant revisions between the study groups. In addition, various radiographic parameters (e.g., glenoid morphology, critical shoulder angle, lateral acromion index, implant sizing [humeral component overhang], radial matching of the humeral and glenoid components, glenohumeral distance, and medial glenoid cement penetration) were evaluated to explore their potential association with revision. A subset of these parameters was subsequently included in the multivariable Cox model on the basis of clinical relevance. Results: After a median postoperative period of 72 months, the overall revision rate was 51%. The reasons for revision were glenoid component loosening (85%), periprosthetic humeral fracture (9%), early rotator cuff failure (3%), and low-grade infection (3%). The median implant survival in patients with primary OA (95 months; 95% confidence interval [CI]: 84 to 108) was significantly longer than that in patients with secondary OA (71 months; 95% CI: 60 to 88; p = 0.027). Female patients had a significantly shorter time to revision than male patients (p = 0.016). There were no significant differences in complications or revision rates by OA pathology. Secondary OA, the presence of medial glenoid cement penetration, and an anterior overhang of the humeral component were associated with an increased risk of revision. Conclusions: Our findings indicate a high rate of glenoid component loosening as the primary cause of revision in patients with primary and secondary OA undergoing stemless aTSA with the Eclipse and a cemented pegged all-polyethylene glenoid component. This outcome emphasizes the need for careful consideration of implant design, patient selection criteria, and implant positioning and cementation in order to optimize implant survival. Level of Evidence: Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Background: Metallic lateralized-offset glenoid reverse shoulder arthroplasty (RSA) for cuff tear arthropathy combines the use of a metallic augmented baseplate with a metaphyseally oriented short stem design that can be applied at a 135° or 145° neck-shaft angle, leading to additional lateralization on the humeral side. Lateralization of the center of rotation decreases the risk of inferior scapular notching and improves external rotation, deltoid wrapping, residual rotator cuff tensioning, and prosthetic stability ^1–4 . Metallic increased-offset RSA (MIO-RSA) achieves lateralization and corrects inclination and retroversion while avoiding graft resorption and other complications of bony increased-offset RSA (BIO-RSA) ^5–8 . Reducing the neck-shaft angle from the classical Grammont design, in combination with glenoid lateralization, improves range of motion ^9,10 by reducing inferior impingement during adduction at the expense of earlier superior impingement during abduction ^2,11 . Lädermann et al. ¹² investigated how different combinations of humeral stem and glenosphere designs influence range of motion and muscle elongation. They assessed 30 combinations of humeral components, as compared with the native shoulder, and found that the combination that allows for restoration of >50% of the native range of motion in all directions was a 145° onlay stem with a concentric or lateralized tray in conjunction with a lateralized or inferior eccentric glenosphere. In addition, the use of a flush-lay or a slight-onlay stem design (like the one utilized in the presently described technique) may decrease the risk of secondary scapular spine fracture ^13,14 . The goal of this prosthetic design is to achieve an excellent combination of motion and stability while reducing complications. Description: This procedure is performed via a deltopectoral approach with the patient in the beach-chair position under general anesthesia combined with a regional interscalene nerve block. Subscapularis tenotomy and capsular release are performed, the humeral head is dislocated, and any osteophytes are removed. An intramedullary cutting guide is placed for correct humeral resection. The osteotomy of the humeral head is performed in the anatomical neck with an inclination of 135° and a retroversion of 20° to 40°, depending on the anatomical retroversion. The glenoid is prepared as usual. The lateralized, augmented baseplate is assembled with the central screw and the baseplate-wedge-screw complex is placed by inserting the screw into the central screw hole. Four peripheral screws are utilized for definitive fixation. An eccentric glenosphere with inferior overhang is implanted. The humerus is dislocated, and the metaphysis is prepared. Long compactors are utilized for proper stem alignment, and an asymmetric trial insert is positioned before the humerus is reduced. Stability and range of motion are assessed. The definitive short stem is inserted and the asymmetric polyethylene is impacted, resulting in a neck-shaft angle of 145°. Following reduction, subscapularis repair and wound closure are performed. Alternatives: BIO-RSA is the main alternative to MIO-RSA. Boileau et al. ¹⁵ demonstrated satisfactory early and long-term outcomes of BIO-RSA for shoulder osteoarthritis. A larger lateral offset may also be achieved with a thicker glenosphere ^2,16 . Mark A. Frankle developed an implant that addressed the drawbacks of the Grammont design: a lateralized glenosphere combined with a 135° humeral neck-shaft angle. The 135° neck-shaft angle provides lateral humeral offset, preserving the normal length-tension relationship of the residual rotator cuff musculature, which optimizes its strength and function. The lateralized glenosphere displaces the humeral shaft laterally, minimizing the potential for impingement during adduction ^2,9,17,18 . The advantage of BIO-RSA and MIO-RSA over lateralized glenospheres is that the former options provide correction of angular deformities without excessive reaming, which can lead to impingement ¹⁹ . Rationale: BIO-RSA has been proven to achieve excellent functional outcomes ^15,20,21 ; however, the bone graft can undergo resorption, which may result in early baseplate loosening. Bipolar metallic lateralized RSA is an effective strategy for achieving lateralization and correction of multiplanar defects while avoiding the potential complications of BIO-RSA ^6,7,22–24 . MIO-RSA also overcomes another limitation of BIO-RSA, namely that BIO-RSA is not applicable when the humeral head is not available for use (e.g., humeral head osteonecrosis, revision surgery, fracture sequelae). Expected Outcomes: A recent study evaluated the clinical and radiographic outcomes of metallic humeral and glenoid lateralized implants. A total of 42 patients underwent primary RSA. Patients were documented prospectively and underwent follow-up visits at 1 and 2 years postoperatively. That study demonstrated that bipolar metallic lateralized RSA achieves excellent clinical results in terms of shoulder function, pain relief, muscle strength, and patient-reported subjective assessment, without instability or radiographic signs of scapular notching ²³ . Kirsch et al. ²⁵ reported the results of primary RSA with an augmented baseplate in 44 patients with a minimum of 1 year of clinical and radiographic follow-up. The use of an augmented baseplate resulted in excellent short-term clinical outcomes and substantial deformity correction in patients with advanced glenoid deformity. No short-term complications and no failure or loosening of the augmented baseplate were observed. Merolla et al. ⁷ compared the results of 44 patients who underwent BIO-RSA and 39 patients who underwent MIO-RSA, with a minimum follow-up of 2 years. Both techniques provided good clinical outcomes; however, BIO-RSA yielded union between the cancellous bone graft and the surface of the native glenoid in <70% of patients. On the other hand, complete baseplate seating was observed in 90% of MIO-RSA patients. Important Tips: When performing subscapularis tenotomy, leave an adequate stump to allow end-to-end repair. Tenotomize the superior part of the subscapularis tendon in an L-shape, sparing the portion below the circumflex vessels. As glenoid exposure is critical, perform a 270° capsulotomy. Continuously check the orientation of the baseplate relative to the prepared hole and reamed surface to ensure accurate implantation of the full wedge baseplate to achieve a proper fit. Aim for 70% to 80% seating of the baseplate onto the prepared glenoid surface. Avoid overtightening or excessive advancement of the baseplate into the subchondral bone. Gaps between the baseplate and glenoid surface should also be avoided. In order to avoid varus or valgus malpositioning of the final implant, obtain proper diaphyseal alignment by following “the three big Ls”: large, lateral, and long. Use a large metaphyseal component to fill the metaphysis. Place the guide pin for the reaming of the metaphysis slightly laterally into the resected surface of the humerus. Use long compactors for diaphyseal alignment to avoid varus or valgus malpositioning of the final implant. Use an intramedullary cutting guide for correct humeral resection. Utilize the correct liner in order to obtain proper tensioning and avoid instability. Acronyms and Abbreviations: K wire = Kirschner wire ROM = range of motion