Inverse relationship between the critical shoulder angle and rotator cuff insertional footprints: an anatomical study

Degenerative shoulder disorders impose a significant clinical and economic burden. The critical shoulder angle (CSA) has been established as a predictor of rotator cuff tears and glenohumeral osteoarthritis, but the anatomical basis underlying those relationships remains incompletely characterized. This study investigates whether the CSA correlates with the size of the rotator cuff muscle insertional footprints.

An anatomical study was performed on 28 shoulders from 14 formalin-fixed cadavers (mean age, 77.15 years; standard deviation, 9.94). Radiographs in the Grashey view were used to measure the CSA. The insertional footprints of the supraspinatus (SSP), infraspinatus (ISP), teres minor (TM), and subscapularis (SSC) were dissected and measured. A correlation analysis was conducted to assess relationships.

A moderate inverse correlation was found between the CSA and the footprint size of all examined muscles: ISP (r=-0.52, P<0.01), TM (r=-0.60, P<0.001), SSP (r=-0.51, P<0.01), and SSC (r=-0.42, P<0.05). Large CSA values were associated with small insertional areas.

This study suggests that a large CSA is associated with significantly smaller-than-average insertional footprints. These findings provide an anatomical basis for biomechanical models that could help to refine risk assessment and preventive strategies for shoulder pathology. Level of evidence: Anatomical study.