A
A retracted full-thickness supraspinatus tear.
B
An avulsion of the inferior glenohumeral ligament (HAGL).
C
A tear of the superior glenohumeral ligament and subscapularis.
D
A longitudinal split tear of the long head of the biceps tendon.
Explanation:The 'comma sign' is formed by the superior glenohumeral ligament (SGHL) and the coracohumeral ligament tearing from the humerus along with the upper border of the subscapularis. It retracts medially and inferiorly, acting as a guide to the superolateral corner of the torn subscapularis. Reference: Lo IK, Burkhart SS, 'The comma sign: an arthroscopic guide to the torn subscapularis', Arthroscopy (2003).