The Comma Sign: The Coracohumeral Ligament and Superior Glenohumeral Ligament Exhibit Similar Quantitative Characteristics With Terminal Confluence at the Subscapularis Insertion

PURPOSE: The purpose of this morphologic cadaveric study was to quantitatively define the composition of the previously described comma tissue along with its relation to the subscapularis tendon insertion. METHODS: Fresh frozen cadaveric shoulder specimens were included for analysis. The coracohumeral ligament (CHL) was exposed at its origin along the base of the coracoid process and freed laterally along its course to the lesser tuberosity adjacent to the bicipital groove. The superior glenohumeral ligament (SGHL) was identified and traced along its course deep to the CHL within the rotator interval with insertion onto the superior aspect of the lesser tuberosity. The midpoint diameters of the SGHL and CHL and their composite insertional diameters on the subscapularis tendon insertion and lesser tuberosity were measured with digital calipers. The mean diameter was determined from 3 measurements taken of each ligament. RESULTS: Eight specimens were included. With the use of digital calipers, the mean midpoint diameters of the SGHL and CHL were identified as 5.99 mm (range, 5.25-6.91 mm) and 5.13 mm (range, 4.28-5.72 mm), respectively. The composite insertional diameter of the SGHL and CHL on both the lesser tuberosity and humeral insertion of the subscapularis tendon was 9.93 mm (range, 6.69-12.05 mm). At its insertion, the SGHL and CHL comprised 54% and 46% of the comma tissue, respectively. Additionally, all specimens were identified as showing a confluence of the SGHL and CHL composite insertion with the subscapularis tendon at the point of its humeral head insertion. CONCLUSIONS: The comma tissue is a pivotal structure for the identification, mobilization, and repair of retracted subscapularis tendon tears. Therefore, quantitative knowledge of the midpoint diameter, insertional diameter, and composite distribution of the CHL and SGHL provided by this morphologic cadaveric analysis may aid surgeons in their efforts to restore the native anatomy. CLINICAL RELEVANCE: Subscapularis tendon tears have often been under-addressed during rotator cuff repair. The comma tissue has been described as an anatomic structure that can aid in the identification, mobilization, and repair of retracted subscapularis tendon tears. Therefore, quantitative knowledge of this important arthroscopic landmark may aid surgeons in their efforts to restore the native anatomy.