Reverse Total Shoulder Arthroplasty Baseplate Screw Trajectory: Are We Trading Fixation for Iatrogenic Risk?

Reverse total shoulder arthroplasty (rTSA) has expanded rapidly in indications and volume, with increasing use for cuff-tear arthropathy, fractures, instability, and revision surgery. Glenoid baseplate fixation remains the primary determinant of implant survivorship. Biomechanical strategies including inferior baseplate tilt, longer anteroinferior screws, and cortical-engaging central fixation, improve stability and reduce micromotion, but may increase proximity to critical neurovascular and cortical structures, increasing the risk of iatrogenic injury. This focused narrative review synthesizes biomechanical, cadaveric, imaging, and clinical studies identified through a structured search of PubMed, Embase, Scopus, and Web of Science from 2005 to 2025. Studies evaluating screw trajectory, fixation mechanics, cortical breach, and neurovascular proximity were qualitatively integrated due to heterogeneity. Across studies, safe screw placement was often limited to narrow margins (<5 mm), with superior and posterior trajectories demonstrating the highest risk of cortical breach and nerve proximity, alongside substantial interpatient variability in anterior bone corridors. Collectively, evidence suggests that strategies maximizing fixation strength may narrow an already limited margin of anatomic safety. Although patient-specific instrumentation (PSI), navigation, and 3D-planning improve accuracy and reproducibility, they do not inherently prevent iatrogenic injury without defined safety constraints. We propose a two-dimensional, anatomy-based “Safe Triangle” for glenoid screw trajectory planning, bounded by the coracoid base anteriorly, suprascapular notch posteriorly, and inferior glenoid rim inferiorly. Within this corridor, inferior and anteroinferior screws may optimize fixation while minimizing iatrogenic injury. This framework provides a reproducible method to balance fixation and safety, with future work needed for prospective validation and integration into surgical planning platforms.