Abstract
Introduction
Glenoid inclination, defined as the angle formed by the intersection of a line made of the most superior and inferior points of the glenoid and a line formed by the supraspinatus fossa, has been postulated to impact the mechanical advantage of the rotator cuff in shoulder abduction. An increase in glenoid inclination has previously been reported in patients with massive rotator cuff tears and multiple studies have correlated rotator cuff tears to an increase of the critical shoulder angle, an angle comprised of both the glenoid inclination and acromical index. Glenoid inclination is best measured by the B-angle as it has been shown to be both an accurate and reliable. The purpose of this study was to determine the correlation of glenoid inclination and the presence of degenerative rotator cuff tears.
Methods
Data was prospectively collected for study patients assigned to one of two groups. The tear group consisted of patients with degenerative, atraumatic rotator cuff tears, confirmed by MRI and the control group consisted of healthy volunteers without shoulder pain. Inclusion criteria for both groups included age 45 or older. Exclusion criteria included history of previous shoulder surgery, previous patient-recalled injury to the shoulder, presence of glenoid weak, and previous humerus or glenoid fracture. Patients were also excluded from the control group if any shoulder pain or history of rotator cuff disease was present. All patients had standard anterior/posterior shoulder radiographs taken and glenoid inclination was digitally measured with Viztek OpalRad PACS software (Konica Minolta, Tokyo, Japan). The beta angle was measured to determine the glenoid inclincation. Statistical analysis was performed using SPSS version 23 (IBM, Aramonk, NY). Patient age and glenoid inclination were examined with the Shapiro-Wilk test of normality and then compared with student t tests. Gender distribution was compared with chi square test. A p-value of 0.05 was used to represent significance.
Results
The study included 26 patients in the tear group and 23 patients in the control group. There was no difference in the age of the two groups (57 vs 54, p=0.292) or gender distribution (p=0.774). The average glenoid inclination was 11.18 (SD=2.67) degrees for the tear group and 5.97 (SD=2.55) degrees for the control group. This difference was statistically significant (p<0.001).
Discussion
Glenoid inclination is significantly increased in patients with degenerative rotator cuff tears compared to healthy controls. Tendon overload secondary to increased glenoid inclination may be the primary anatomical factor contributing to the development of degenerative rotator cuff tears.
