Symptomatic rotator cuff tears (RCTs) are common, with more than 270,000 repairs performed in the United States each year, 86% of which are performed on patients age 45 and older.1 While the causes of nontraumatic RCTs are multifaceted and poorly understood, distinct variations in the scapular anatomy, such as superior glenoid inclination and a large acromial index, are associated with degenerative RCTs. The critical shoulder angle (CSA) is a radiographic parameter that accounts for both the glenoid inclination and the lateral acromion extension. A CSA >35 has been identified as a risk factor for RCTs, and a CSA <30 is associated with an increased prevalence of osteoarthritis, suggesting that patients with a CSA between these values are at the lowest risk for either condition.
Few studies have looked at how scapular anatomy influences patient outcomes after treatment of RCTs. In one study, patients with a large acromial index who underwent arthroscopic repair of full-thickness RCTs had lower patient satisfaction scores when compared with those with a small acromial index. Furthermore, in a long- term follow-up of patients who underwent latissimus dorsi tendon transfer for irreparable RCTs, patients with a significantly larger CSA reported inferior outcomes.
The fact that the scapular anatomy is not associated only with prevalence of RCTs but is also associated with inferior patient outcomes has led to the idea that an arthroscopic reduction of a large CSA (>35 ) to a favorable range may be beneficial to reduce the risk of primary RCTs, rotator cuff retears, and unsatisfactory outcomes after treatment of RCTs for this patient population.
Anatomical cadaveric studies have demonstrated that the CSA can be significantly reduced by arthroscopic lateral acromioplasty (ALA).16,17 However, there is a risk of potentially damaging the deltoid origin during acromioplasty, which may lead to postoperative deltoid avulsion.18,19 Although it was reported that the deltoid origin was not macroscopically damaged by ALA,16,17 it still remains unclear whether ALA affects the me- chanical integrity of the deltoid. The purpose of this study was to determine whether a 5-mm and/or 10-mm ALA would weaken the structural and mechanical integrity of the lateral deltoid. It was hypothesized that ALA would not significantly affect the failure load of the lateral deltoid origin.