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Objectives and questions: Shoulder degenerative conditions are common and financially burdensome. Alongside the acromion index and the lateral acromion angle, the critical shoulder angle (CSA) was the strongest predictor for rotator cuff tears. As the size of the CSA influences the joint shear and load on the rotator cuff muscles, our study aimed to evaluate whether there is a correlation between the size of the CSA and the insertional footprint of the rotator cuff muscles to counteract the forces.

Material and methods: For the present anatomical study, 28 shoulder joints of 14 formalin embalmed donors (8 male, six female) were available. A calibrated image was acquired perpendicular to each tendon insertion, with a millimeter scale next to the sample placed at the footprint level. The Pearson correlation coefficient was calculated to analyze the linear correlation between the insertional footprints and the CSA and find coherence.

Results: In the present study, we found an inverse correlation between the CSA and the insertional footprints of the rotator cuff muscles. For the ISP (r=-0.52), TM (r=-0.60), SSP (r=-0.51), and SSC (r=-0.42), a moderate negative relationship was found.

Discussion and conclusions: This study demonstrates an inverse correlation between the critical shoulder angle (CSA) and the insertional footprint size of rotator cuff muscles, suggesting that larger CSAs are associated with smaller footprints and increased shear forces. In comparison, smaller CSAs correspond to larger footprints and greater compression forces. These findings provide new anatomical insights into the relationship between scapular morphology and rotator cuff pathology, reinforcing the biomechanical implications of CSA in shoulder degeneration.