The Effects of Arthroscopic Lateral Acromioplasty on the Critical Shoulder Angle and the Anterolateral Deltoid Origin: An Anatomic Cadaveric Study

PurposeTo investigate if (1) an anterolateral acromioplasty and (2) a lateral acromion resection alter the critical shoulder angle (CSA) without affecting the deltoid origin.MethodsFirst, the native CSAs of 10 human cadaveric shoulders (6 male and 4 female specimens; mean age, 54.2 years) were determined with the use of fluoroscopy. Setup allowed for consistent repetitive measurements. Next, a standard arthroscopic anterolateral acromioplasty was performed to create a type 1 acromion, and the CSA was reassessed fluoroscopically. Afterward, a lateral acromioplasty was performed with a 5-mm lateral acromion resection using a 5-mm burr, and the CSA was measured again. The native CSA was compared with (1) the CSA after acromioplasty and (2) the CSA after acromioplasty and lateral acromion resection using a paired t test. Finally, the acromial deltoid attachment was evaluated anatomically for damage to the anterolateral origin.ResultsThe mean native CSA (34.3° ± 2.1°) was reduced significantly by acromioplasty (33.1° ± 2.0°, P < .001) and further reduced by lateral acromion resection (31.5° ± 1.7°, P < .001). Anterolateral acromioplasty reduced the CSA by a mean of 1.4° (95% confidence interval boundaries, 0.8° and 1.9°), and in combination with lateral acromion resection, the CSA was reduced by a mean of 2.8° (95% confidence interval boundaries, 2.1° and 3.5°). In all specimens (5 of 5) with a presurgery CSA of 35° or greater, the CSA was reduced to the range of 30° to 35° by the combination of both techniques. However, in 2 specimens with a CSA of approximately 32°, the CSA was reduced to less than 30°. The acromial deltoid attachment was found to be well preserved in all specimens.ConclusionsArthroscopic anterolateral acromioplasty and a 5-mm lateral acromion resection each reduced the CSA significantly and did not damage the deltoid origin.Clinical RelevanceThe combination of both techniques could potentially be used in clinical practice to reduce a CSA greater than 35° to the desired range of 30° to 35°.