In 1981, Turkel et al. described the IGHL as a structure attached to the inferior, anterior, and posterior margins of the glenoid labrum just below the epiphyseal line and the humeral neck (42). In fetal development, the IGHL is present by 14-wk gestation and appears as several layers of poorly organized collagen fibers, which are better organized than their surrounding capsular structure. With gestational time, the amount of fibrous tissue increases while the cellularity decreases (14,43).
The three glenohumeral ligaments are named for the location of their origins on the humeral head. The IGHL origin is just below the articular margin on the inferior humeral head (15,44). Ticker et al. observed that the IGHL has an anterior and posterior insertion into the humerus. The anterior insertion is inferior to the lesser tuberosity, whereas the posterior insertion is inferior to the greater tuberosity, with an equal distribution between V-shaped (with the axillary pouch forming the apex of the V) and collar-like (entire IGHL attached inferior to the humeral head articular edge) attachments (45).
The IGHL passes beneath the humeral head to insert primarily into the anterior inferior glenoid. But the IGHL also inserts posteriorly into the posterior labrum and capsule and has an axillary insertion directly into the bone. In the labrum attachment, transitional zones of fibrocartilage and mineralized fibrocartilage are present between the IGHL and glenoid bone. The fibrocartilage zone and glenoid attachments both have a variable thickness, which decreases in the inferior direction along the glenoid (46,47).
The IGHL appears as a triangular structure that extends between the glenoid labrum, triceps tendon, and the subscapularis muscle (48). As noted by Turkel, the anterosuperior edge of the ligament is significantly thickened and termed the superior band of the IGHL. There are also thickenings in the anteroinferior portion of the joint capsule, which Turkel termed the "axillary pouch." This pouch could be divided into two portions: the anterior and posterior axillary pouch. The anatomic locations of the three IGHL bands are demonstrated in Fig. 4 (42).
In contrast, O'Brien noted the IGHL was comprised of a superior band, posterior band, and an axillary pouch in which both anterior and posterior bands of IGHL were
thickenings of the surrounding joint capsule. These bands showed well organized collagen bundles running in the coronal plane (from the humerus to the glenoid). In the axillary pouch, the bundles were thicker but less well-organized with intermingling of fibers from inner and middle capsular layers. The posterior capsule appeared thinner than the anterior capsule (44). However, further studies by Ticker et al. identified a posterior band in only a small percentage (12.5%) of shoulders examined (45). The difference between these observations may be a result of the external rotation of the upper arm. As the arm is externally rotated, the posterior axillary pouch folds on itself and appears to actually be a thickening of the joint capsule.
The IGHL helps to form the anterior border of the glenohumeral joint complex. In this area of the joint capsule, a predominantly radial orientation of the fiber bundles exists. Microscopic evaluation reveals crossing of superficial fiber bundles, oriented in a circular manner. Fibers of the middle glenohumeral ligament (MGHL) also have a role in this area of the joint capsule (Fig. 5; 55).
Geometric Properties of the IGHL
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