While we know that many patient (osteoporosis, steroid use, inflammatory arthropathy, female sex) and shoulder factors (cuff status, prior surgery, coracoacromial arch integrity, humeral and glenoid deformity) drive the outcome of reverse shoulder arthroplasty, I was curious to see what the literature has to say about the surgeon-controlled variables related to the geometry of the reconstruction. I've tried to focus on the position, rather than the design, of the components. Here's what I think I learned - as always - your comments are welcome.
Avoiding Complications
Minimizing risk of inferior impingement, scapular notching, and baseplate loosening
Place the baseplate flush with the inferior glenoid rim
Select and place humeral component to achieve a 135° liner-shaft angle
Target 4–10 mm of lateralization of the glenosphere center of rotation (CO): defined as the distance from the glenosphere center of rotation (COR) to the glenoid bone surface (includes the thickness of the baseplate, bone graft and/or augment). Know your glenospheres and don't rely on the numbers on the box: for example, in one implant system the 3mm baseplate plus a "32-4" glenosphere lateralizes the center of rotation by 9mm.
Place baseplate in 0 - 10 degrees of inferior tilt: central screw parallel to floor of supraspinous fossa so that the humeral force on the glenosphere is perpendicular to the screw fixation.
Minimizing risk of neurologic injury and pain.
Avoid excess humeral distalization: acromiohumeral interval (AHI) <30mm, humeral lengthening (pre to postoperative change in AHI) <20mm.
Minimizing risk of acromial and scapular spine fracture
The distance from the glenosphere center (COR) to the most lateral point on the acromial undersurface (DA) should exceed the distance from the glenosphere center (COR) to the lateral tip of the greater tuberosity (DGT). DA ≥ DGT.
Minimize humeral-sided contribution to global lateralization. Humeral sided lateralization directly increases the distance from the glenosphere center (COR) to the lateral tip of the greater tuberosity (DGT) while leaving the distance from the glenosphere center (COR) to the most lateral point on the acromial undersurface (DA) unchanged, worsening the DA - DGT difference. By contrast glenoid-sided lateralization (increasing lateralization of the glenosphere center of rotation (CO), changes both the DA and DGT simultaneously, preserving more control over the DA - DGT difference.
Minimizing instability risk
Strive for humeral retroversion 0°–20° and glenoid retroversion 0°–20° (Recall that soft tissue tension, humero-scapular impingement, liner geometry, and other factors play major roles in rTSA stability).
Optimizing Function
Deltoid efficiency
Position the glenosphere center of rotation inferiorly and posteriorly to maximize the deltoid's mechanical advantage during abduction and flexion
Motion
4–10 mm glenoid-sided lateralization improves internal rotation by displacing the humeral cup away from the scapular neck, reducing the impingement that limits motion.
Glenoid retroversion 0°–20° optimizes external rotation
A 135° liner-shaft angle increases adduction and rotational range
Avoid excess humeral distalization: Keeping acromiohumeral interval (AHI) <30mm, humeral lengthening (change in AHI) <20mm facilitates flexion and external rotation.
"Glenosphere Lateralization" - Resolving the Nomenclature Confusion
The geometry of reverse shoulder arthroplasty reconstruction is frequently discussed in terms of a single number ("glenoid lateralization” , "metallic offset", "lateralization shoulder angle (LSA)), yet none of these numbers captures the important surgeon-controlled variables and their use results in contradictory results in the rTSA literature.
Three distinct measurements describe different aspects of glenosphere construct geometry.
Global Lateralization (GL): distance from the glenoid bone surface to the lateral tip of the greater tuberosity (= GT + humeral component contribution). Includes the baseplate and augments. This is the distance that the tuberosity is lateralized from the native glenoid bone. Increases in GL tighten the shoulder - increasing stability, but may also increase the risk of contact between the tuberosity and the acromion when the arm is elevated.
All three are measured from the same landmark (glenoid bone surface) but to different endpoints. Each can vary independently of the others through implant selection and surgical technique. Reporting all three measures on postoperative radiographs would resolve most of the apparent conflicts.
A clear-eyed view
Union Bay Natural Area
2019
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References
1. Arenas-Miquelez A, Murphy RJ, Rosa A, Caironi D, Zumstein MA. Impact of Humeral and Glenoid Component Variations on Range of Motion in Reverse Geometry Total Shoulder Arthroplasty: A Standardized Computer Model Study. J Shoulder Elbow Surg. 2021.
2. Dean EW, Dean NE, Wright TW, et al. Clinical Outcomes Related to Glenosphere Overhang in Reverse Shoulder Arthroplasty Using a Lateralized Humeral Design. J Shoulder Elbow Surg. 2022. [Note: “overhang” is measured as glenosphere-to-baseplate offset on 2D Grashey radiograph, not glenosphere-to-native-bone.]
3. Pak T, Kilic AI, Ardebol J, et al. Glenoid-Sided Lateralization Decreases Scapular Notching With a 135° Humeral Component Arthrex Reverse Shoulder Arthroplasty. J Shoulder Elbow Surg. 2025.
4. Meisterhans M, Bouaicha S, Meyer DC. Posterior and Inferior Glenosphere Position in Reverse Total Shoulder Arthroplasty Supports Deltoid Efficiency for Shoulder Flexion and Elevation. J Shoulder Elbow Surg. 2019.
5. Rai AA, LeVasseur CM, Kane GE, et al. Glenosphere Tilt and Size Predict Shoulder Kinematics During the Hand-to-Back Motion After Reverse Shoulder Arthroplasty. J Orthop Res. 2025.
6. Berton A, Longo UG, Gulotta LV, et al. Humeral and Glenoid Version in Reverse Total Shoulder Arthroplasty: A Systematic Review. J Clin Med. 2022.
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8. Lee HH, Park SE, Ji JH, Jun HS. Mid-Term Comparative Study Between the Glenoid and Humerus Lateralization Designs for Reverse Total Shoulder Arthroplasty. BMC Musculoskelet Disord. 2023.
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10. Wolf GJ, Reid JJ, Rabinowitz JR, et al. Does Glenohumeral Offset Affect Clinical Outcomes in a Lateralized Reverse Total Shoulder Arthroplasty? J Shoulder Elbow Surg. 2022.
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12. Neyton L, Nigues A, McBride AP, Giovannetti de Sanctis E. Neck Shaft Angle in Reverse Shoulder Arthroplasty: 135 vs. 145 Degrees at Minimum 2-Year Follow-Up. J Shoulder Elbow Surg. 2023.
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17. Ameziane Y, Audigé L, Schoch C, et al. Mid-Term Outcomes of a Rectangular Stem Design With Metadiaphyseal Fixation and a 135° Neck-Shaft Angle in Reverse Total Shoulder Arthroplasty. J Clin Med. 2025.
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19. Mollon B, Mahure SA, Roche CP, Zuckerman JD. Impact of Scapular Notching on Clinical Outcomes After Reverse Total Shoulder Arthroplasty: An Analysis of 476 Shoulders. J Shoulder Elbow Surg. 2017.
20. Simovitch R, Flurin PH, Wright TW, Zuckerman JD, Roche C. Impact of Scapular Notching on Reverse Total Shoulder Arthroplasty Midterm Outcomes: 5-Year Minimum Follow-Up. J Shoulder Elbow Surg. 2019.
21. Spiry C, Berhouet J, Agout C, Bacle G, Favard L. Long-Term Impact of Scapular Notching After Reverse Shoulder Arthroplasty. Int Orthop. 2021.
22. Erickson BJ, Werner BC, Griffin JW, et al. A Comprehensive Evaluation of the Association of Radiographic Measures of Lateralization on Clinical Outcomes Following Reverse Total Shoulder Arthroplasty. J Shoulder Elbow Surg. 2022;31:963–970. [Multiple authors report financial relationships with Arthrex, Inc., manufacturer of the implant system used in this study.]
23. Werner BC, Lederman E, Gobezie R, Denard PJ. Glenoid Lateralization Influences Active Internal Rotation After Reverse Shoulder Arthroplasty. J Shoulder Elbow Surg. 2021;30:2498–2505.
24. Southam BR, Bedeir YH, Johnson BM, et al. Clinical and Radiological Outcomes in Lateralized Versus Nonlateralized and Distalized Glenospheres in Reverse Total Shoulder Arthroplasty: A Randomized Control Trial. J Shoulder Elbow Surg. 2023.
25. Longo UG, Gulotta LV, De Salvatore S, et al. The Role of Humeral Neck-Shaft Angle in Reverse Total Shoulder Arthroplasty: 155° Versus <155° — A Systematic Review. J Clin Med. 2022.
