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Basic Science-Anatomy

The anatomy of the LHB has been thoroughly examined and little controversy exists in this realm. The LHB originates at and around the supraglenoid tubercle. Although it is intra-articular, it is extrasynovial. Its blood supply is dependant on the portion of tendon in question.

The proximal and middle portions receive blood supply from branches of the anterior humeral circumflex artery and the distal third of the tendon receives nourishment from branches of the deep brachial artery. The blood supply is markedly reduced in the portion of the tendon which slides in the bicipital groove.

Habermayer et al. It  demonstrated LHB origin from the supraglenoid tubercle in 20% of specimens, origin from the posterosuperior labrum in 48%, and origin from both the labrum and tubercle in 28%. Pal et al. It demonstrated the major origin from the supraglenoid tubercle in 25% and from the posterosuperior labrum in 70%. The association between the biceps tendon and the superior labrum was further examined by Vangsness et al.

It classified the origin into four types.

Type I (22% of specimens) demonstrated origin entirely from the posterior labrum;

Type II (33%) demonstrated primarily posterior attachment with small anterior labral component;

Type III (37%) demonstrated equal anterior and posterior labral components; and

Type IV (8%) demonstrated only anterior labral contribution.

The close relationship between the biceps and the labrum was further supported by Cooper et al.It demonstrated an intimate relationship between the collagen fibrils of the two structures.

The length of the tendinous portion of the LHB measures approximately 9 cm and the musculotendinous junction is at the level of the deltoid and pectoralis major insertions. Its shape is relatively flat at its origin, becoming more tubular as it proceeds distally and into the intertubercular groove. McGough et al. It examined the tensile properties of the LHB and demonstrated that it is weakest at the midpoint— where all his experimental specimens ruptured.

The course of the LHB is from the posterosuperior aspect of the glenoid obliquely over the top of the humeral head. It then enters the bicipital (intertubercular) groove. This groove is formed by the confluence of the lesser tuberosity (anteriorly) and the greater tuberosity (superiorly). Anatomic studies have demonstrated varying depths of the groove (average = 4.3 mm) and varying inclination of the walls of the groove. Ueberham et al.

It described a ridge on the upper portion of the lesser tuberosity (termed a supratubercular ridge) in 45% of anatomic specimens, which was postulated to “push” the biceps anteriorly. Although some authors have suggested that a shallow inclination of the groove predisposes to dislocation, others have found no such association.The most critical anatomical consideration to understand regarding the LHB is that of its stabilizing structures.

Specifically, a thorough understanding of the rotator interval is essential. The rotator interval is the triangular interval bordered superiorly by the anterior margin of the supraspinatus, inferiorly by the superior margin of the subscapularis, and medially by the anterior aspect of the glenoid. Within this triangular space exists anterior glenohumeral capsule as well as the coracohumeral ligament (CHL) and the superior glenohumeral ligament (SGHL). The SGHL and the medial head of the CHL join to form a medial sling for the LHB and this is the major restraint to medial subluxation/dislocation of the LHB.

The CHL originates from the base of the coracoid process and divides into two bands—a superior band, which inserts into the anterior supraspinatus, and an inferior band whose medial head inserts into the superior subscapularis and then onto the superior aspect of the lesser tuberosity. The SGHL also contributes to this medial sling as it courses from the anterior labrum (just anterior to the biceps origin) and inserts onto the superior aspect of the lesser tuberosity.

The fibers of the medial head of the CHL are much more robust and structurally important to the medial sling than the fibers of the SGHL. This sling is critical in preventing the LHB from displacing medially onto the lesser tuberosity. In this way, the sling protects the proximal insertion of the subscapularis from the stresses that would result from a medially displaced LHB.

The medial sling and its relationship to the biceps tendon has been described as “the comma sign”. This comma sign is an arthroscopic description of the aforementioned anatomy of the medial sling and was so named because of its arthroscopic appearance. The comma sign consists of the medial head of the CHL and SGHL (medial sling of the biceps) intersecting with the superior border of the subscapularis. Although the comma sign is visible in the absence of pathology, it is much more prominent, recognizable, and useful in the presence of a torn and retracted subscapularis tendon.

When the subscapularis is torn from its insertion on the lesser tuberosity, the medial sling of the biceps is also pulled off and its association maintained with the subscapularis. Identification of this comma structure is critical when searching for the subscapularis tendon because it is always located at the superolateral border of the subscapularis tendon.

Historically, it was felt that the transverse humeral ligament was the vital structure in regards to retaining the biceps within the bicipital groove ; however, this view has been challenged. Paavolainen et al.They cut the transverse humeral ligament in cadaver specimens but were still unable to dislocate the biceps tendon.

Also, Gross  reported on a technique of arthroscopic release of the sheath of the biceps tendon. In this technique the transverse humeral ligament was divided yet postoperative dislocation or subluxation of the biceps tendon did not occur. Gross emphasized that the CHL be preserved with this technique to prevent biceps instability.

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