Gerber C, et al. - In this present study, the authors examine whether arthroscopic lateral acromioplasty reliably decreases the critical shoulder angle (CSA) and if it is correlated with damage to the deltoid or other complications. In addition to arthroscopic rotator cuff repair (RCR), arthroscopic lateral acromioplasty can reduce the CSA without significantly compromising the deltoid origin, deltoid muscle, or function. It is not correlated with any additional complications of arthroscopic RCR. Insufficiently corrected, abnormally large CSAs are correlated either with a higher retear rate or with the inferior strength of abduction if the tears heal.