The Comma Sign: An Anatomic Study

The "comma sign" is a comma-shaped arc of tissue located at the superolateral edge of the subscapularis at its insertion on the humeral head. It consists of the coracohumeral ligament (CHL) and the superior glenohumeral ligament (SGHL). It was recently recognized as an important landmark to aid surgeons in identifying the edge of a torn subscapularis tendon. The exact proportion of CHL and SGHL has not been precisely defined. The goal of this study was to dissect and more accurately define the composition of the comma tissue and its exact relationship to the subscapularis tendon. A total of 8 fresh frozen cadaveric shoulder specimens (mean age, 74 years; 5 male, 3 female) were dissected via a wide deltopectoral approach. Anatomic landmarks were identified, and measurements were taken with a digital caliper. The midpoint width of the SGHL and CHL and the composite insertion width of the subscapularis were measured. Measurements were taken 3 times each and averaged to calculate mean width. Mean midpoint width of the SGHL, CHL, and composite insertion was 5.99 mm (range, 5.25-6.91 mm), 5.13 mm (range, 4.28-5.72 mm), and 9.93 mm (range, 6.69-12.05 mm), respectively. The comma sign consists of approximately half SGHL (54%) and half CHL (46%) at its insertion to the subscapularis tendon, with an approximate width of 1 cm. With the increase in arthroscopic subscapularis repairs, knowledge of these dimensions will aid surgeons in discerning the comma tissue from other capsular elements and ultimately help in surgical restoration of native anatomy.