The geometry of the bony articulation is inherently unstable. The rotator cuff is a dynamic stabilizer and the capsulolabral tissues are considered static stabilizers. With the arm at 90 degrees abduction, the anterior band of the inferior gleno-humeral ligament complex is the primary static stabilizer to anterior translation. The middle (MGHL) resists anterior translation at 45 degrees of abduction. The superior (SGHL) resists inferior translation with the arm at one's side.
O'Brien et al. describe the functional anatomy of the inferior gleno-humeral complex based on a series of cadaveric dissections. They note that its orientation and design support the functional concept of this single structure as an important anterior and posterior stabilizer of the shoulder joint. The Burra paper is a review of acute upper extremity instability in athletes.
Shoulder pain and instability are common orthopedic problems. Although there are many causes of shoulder pain and instability (including fractures and rotator cuff tears), injuries to the glenohumeral ligaments, labrum, and biceps labral complex are often the cause. Its high spatial resolution, excellent image contrast, and multiplanar capabilities make MRI an excellent tool in the evaluation of the labrum. MR allows accurate depiction of the size and location of labral tears and their associated capsular and glenohumeral ligament injuries. Normal variants that can mimic pathology are also well depicted on MR imaging.
Glenohumeral ligaments (superior, middle and inferior) – Consists of three bands, which runs with the joint capsule from the glenoid fossa to the anatomical neck of the humerus. They act to stabilise the anterior aspect of the joint.