Coracohumeral Ligament

Anatomy

The coracohumeral ligament (CHL) is a trapezoidal ligament located in the superior part of the shoulder capsule (on its nonarticulating surface) and runs parallel to and is closely overlaid by the CAL. It is present in fetal development by 14-wk gestation as a small band of tissue between the CHL and the CAL.

The origin of the CHL is at the most posterior point on the lateral aspect of the coracoid process base (deep relative to the origin of the CAL). It appears as a broad band (2.5 cm wide) and stretches from the root of the coracoid to about 1 cm from the coracoid tip (covering approximately two thirds of the length of the coracoid process).

The superior portion of the CHL originates on the medioposterior portion of the cora-coid, whereas the inferior portion of the CHL originates 1 cm medially of the coracoid tip (4,14,20,26-30).

The CHL passes over the top of the shoulder and fans out laterally before joining the shoulder capsule. A small segment of the CHL blends with the rotator cuff attachments as it attaches to the anterior aspect of the greater humeral tuberosity. A larger segment extends posteriorly through the joint capsule (beneath the infraspinatus and over the bicep tendons) to attach to the lesser tuberosity of the humerus. By attaching on either side of the bicipital groove, the CHL provides a tunnel for the biceps tendon. Renditions of the CHL in the various layers of the rotator interval are shown in Fig. 3 (20,26, 28,31,32).

The CHL displays distinct anterior and posterior borders (32). On its lateral side, the CHL covers the interval between the anterior border of the supraspinatus muscle and superior border of the subscapularis muscle and tendon. At the lesser tuberosity, the CHL blends with the insertion of the subscapularis tendon. In its inferior direction, the CHL joins with the superior glenohumeral ligament (SGHL) (28).

Geometry

The CHL has a variable thickness, which is demonstrated by the fanning of the cross-sectional area along its distal length (toward the humerus) with a midpoint value of 53.7 ± 3.2 mm2. Additionally, the CHL displays a variable humeral insertion with 75% of CHL specimens inserting into the rotator interval between the supraspinatus and subscapularis tendons, rather than a direct bony insertion. An additional 25% of CHLs insert into the supraspinatus tendon. Cooper demonstrated some variability in CHL appearance, finding well-defined structures in only 76% of shoulders examined. In the remaining shoulders, the CHL appeared only as a fold in the anterosuperior glenohumeral capsule (15,27,33,34).

Structure and Histology

Histologically, the deep layer of the CHL (on the articular side) forms a portion of the superior capsule. Conversely, the superficial layer partly covers the bursal side and is embedded in fatty tissue with only a few collagen fiber bundles present. There is only a clear demarcation between the CHL and other surrounding fiber bundles in 16.3% of observations (35).

The superior portion of the CHL shows an irregular organization of collagen fibers that are interspersed with loose connective tissue and filled with fat and blood vessels. The inferior portion of the CHL has an anterior region of disorganized collagen fibers and a posterior region with distinct bundles of collagen fibers (30).

Biomechanics

Elastic Response

Structural and Material Properties

During mechanical testing at a strain rate of 100 mm/min, all CHL specimens failed in the proximal ligament substance near the coracoid insertion. The ultimate load of the CHL is 359.8 ± 40.3 N, corresponding to a stress of 6.7 MPa. The stiffness of the CHL is 36.7 ± 5.9 N/mm. The CHL absorbs 2285 ± 378.2 N-m of energy and stretches 35.9

Delamination Tear Rotator Cuff

Fig. 3. (A) Anterolateral view of the right shoulder rotator interval that demonstrates the superior layer of the lateral rotator interval (L), which contains the superior layer of the CHL. These CHL fibers extend from the coracoid process (CP) to the insertions of the subscapularis (SSC) and supraspinatus (SSP) muscles. (B) Second layer of the rotator interval of the same shoulder. Fibers of the SSP and subscapularis blend with CHL fibers. (C) The third layer of the rotator interval from the same shoulder, showing deep CHL fibers inserting into the greater tuberosity (GT) and lesser tuberosity (LT). A, anterior covering band of long-head biceps tendon; M, medial rotator interval; ISP, infraspinatus muscle; AC, acromion. (Reprinted from ref. 33).

Fig. 3. (A) Anterolateral view of the right shoulder rotator interval that demonstrates the superior layer of the lateral rotator interval (L), which contains the superior layer of the CHL. These CHL fibers extend from the coracoid process (CP) to the insertions of the subscapularis (SSC) and supraspinatus (SSP) muscles. (B) Second layer of the rotator interval of the same shoulder. Fibers of the SSP and subscapularis blend with CHL fibers. (C) The third layer of the rotator interval from the same shoulder, showing deep CHL fibers inserting into the greater tuberosity (GT) and lesser tuberosity (LT). A, anterior covering band of long-head biceps tendon; M, medial rotator interval; ISP, infraspinatus muscle; AC, acromion. (Reprinted from ref. 33).

± 11.9% prior to failure. This suggests that although the CHL is a capsular thickening, it displays similar biomechanical behavior to ligaments (34).

In Situ Loads

With applied external anterior loading, the CHL carries internal loads at all angles of abduction. However, during posterior loading, the CHL's maximum in situ load is observed at 0° of abduction, and decreases with increasing abduction angles (36).

Stability

The CHL resists anterior and posterior subluxation of the humeral head (32). During internal rotation, the CHL contributes to the subluxation force; in neutral rotation, the CHL is a primary anterior constraint of the glenohumeral joint (37,38). The CHL also limits external rotation and prevents inferior subluxation (28). With the inferior glenohumeral ligament (IGHL), the CHL is the primary restraint to external rotation in abduction (39). The CHL (with the SGHL) contributes to joint constraint in both anterior and posterior load application (36). Inferior stabilization by the CHL may be proportional to compressive loads and displacements (40).

The CHL becomes taut in flexion and external rotation of the shoulder, as well as in anterior and posterior translation of the humeral head. During lateral motion, CHL tightening occurs earlier than during medial rotation. Therefore, release of the CHL may aid in the treatment of frozen shoulders (20,41).

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