Miyake S, Tamai M, Takeuchi Y, et al. - This study was intended to verify where and what damage occurs at the acromial undersurface in patients with rotator cuff tears. Researchers conducted arthroscopic shoulder (n = 182, all with rotator cuff tears; mean age, 64.9 ± 8.4 years) and cadaveric shoulder (n = 23, 14 intact cuffs and 9 rotator cuff tears; mean age, 74.8 years) assessments to observe the extent and degree of damage to the acromial undersurface. The relationship between the severity of the damage was examined to the acromial undersurface (assessed using the Copeland-Levy classification as A0, normal; A1, minor scuffing; A2, major damage; or A3, visualization of bare bone area) and rotator cuff tear size (assessed using the classification of DeOrio and Cofield as partial; small, < 1 cm; medium, 1-3 cm; or large or massive, > 3 cm). The findings reveal that in patients with rotator cuff tears, damage to the acromial undersurface occurred at the middle, posterior, and anterior one-third areas, and the degree of damage was associated with cuff tear size. For subacromial impingement damage, surgeons should evaluate the entire acromial undersurface to check at the middle and posterior one-third areas as well as the anterior one-third area of the acromial undersurface; this might aid in the treatment of patients with rotator cuff disease or subacromial impingement syndrome.