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

      Introduction

      A critical shoulder angle (CSA) greater than 35° is associated with rotator cuff tears (RCTs). Reduction of a CSA greater than 35° to the “favorable” range of 30-35° may potentially lower the risk of primary RCTs or decrease re-tears after rotator cuff repair. The aims of this study were to investigate if (1) a standard acromioplasty and (2) a lateral acromion resection alters the CSA without affecting the deltoid origin.

      Methods

      First, the native CSAs of 10 human cadaveric shoulders (6 male, 4 female, average age 54.2 years) was determined with the use of fluoroscopy. The test setup allowed for consistent repetitive measurements. Next, a standard arthroscopic anterolateral acromioplasty was performed and the CSA was then re-assessed fluoroscopically. Then, a lateral acromioplasty was performed with a 5mm lateral acromion resection using a 5mm burr, and the CSA was measured again. The native CSA was compared to: (1) the CSA after acromioplasty and (2) the CSA after lateral acromion resection using a paired t-test. Finally, the acromial deltoid attachment was evaluated anatomically for damage to the anterolateral origin.

      Results

      The average native CSA (34.3±2.1°) was reduced significantly (p<0.001) by standard acromioplasty (mean CSA= 33.1±2.0°) and was further reduced by lateral acromion resection (mean CSA= 31.5±1.7°; p<0.0001). In three specimens with a pre-surgery CSA greater than 35°, the CSA was reduced to the desired range of 30-35° by the combination of a standard anterolateral acromioplasty and a 5mm lateral acromion resection. The acromial deltoid attachment was found to be well-preserved in all specimens.

      Conclusion

      Standard arthroscopic acromioplasty as well as a 5mm lateral acromion resection each reduced the CSA significantly and did not damage the deltoid origin. Future investigations will determine whether the combination of both techniques can be used in clinical practice to reduce a CSA >35° to the desired range of 30-35°.