Scapular Morphometry Informs Suprascapular Nerve Injury Risk During Reverse Shoulder Arthroplasty: A Cadaveric Study

<b>Background</b>: Reverse shoulder arthroplasty (RSA) relies on secure baseplate fixation to the glenoid. This carries a risk of suprascapular nerve (SSN) injury during peripheral screw insertion. Although fixed safe zones have been described, it remains unclear whether these scale with scapular morphometry or whether common screw positions confer differential SSN risk. <b>Methods:</b> Twenty cadaveric shoulders (ten pairs) were dissected. The superior safe zone (distance from the supraglenoid tubercle to SSN at the suprascapular notch) and posterior safe zone (distance from the glenoid rim to SSN at the spinoglenoid notch) were measured. Scapular dimensions (height, spine length, width) were measured. In ten shoulders, simulated RSA baseplate fixation was performed with superior screws placed at 11, 12, or 1 o'clock and posterior screws at 8, 9, or 10 o'clock. Screw lengths were based on glenoid depth. Cortical breach and SSN proximity were recorded. Linear regression assessed relationships between scapular dimensions and safe zones. <b>Results:</b> The superior safe zone (mean 2.9 ± 0.5 cm) significantly correlated with scapular dimensions (r = 0.78-0.86; <i>p</i> < 0.0001). All superior screws remained intraosseous across configurations. The posterior safe zone (1.9 ± 0.6 cm) showed no correlation. Posterior cortical breach occurred in 50% of specimens across all tested positions and was associated with smaller scapular spine length (<i>p</i> = 0.027). No significant difference in SSN proximity was observed between posterior screw positions. <b>Conclusions:</b> Scapular dimensions predict the superior, but not posterior, safe zone. Scapulae with shorter spine lengths demonstrated increased risk of posterior cortical breach, independent of screw position. These findings establish anatomical scalability of the superior safe zone and suggest that scapular morphometry may inform preoperative RSA planning; however, prospective validation is needed before routine clinical implementation.