Long Head of Biceps Tendon

The Long Head of Biceps Tendon (LHB) arises from within the glenohumeral joint from both the supraglenoid tubercle and the adjacent glenoid labrum.

It’s likely a significant pain generator in a variety of shoulder conditions. Therefore, pathology related to the LHB tendon should be assessed in any patient with a condition related to the glenohumeral joint.

Long Head of Biceps Tendon Anatomy

The biceps brachii, innervated by the musculocutaneous nerve, has two heads that originate from different points on the scapula. The short head arises from the coracoid process as a single tendon combined with the coracobrachialis muscle (the conjoined tendon) and the long head arises from within the glenohumeral joint from both the supraglenoid tubercle and the adjacent glenoid labrum. The tendon travels anterolaterally in the rotator interval and exits the joint through the bicipital groove which lies between the greater and lesser tuberosities of the proximal humerus. Travelling distally, the muscle bellies of each head coalesce, cross the cubital fossa and spiral towards their primary insertion on the bicipital tuberosity on the proximal radius.

The supraglenoid tubercle of the scapula has historically been described as the origin of the Long Head of Biceps Tendon. However, several cadaveric studies have found that the superior labrum contributes significantly to the LHB origin.

The torsional strain placed upon the superior labrum by the LHB tendon in positions of hyperabduction and external rotation is at least one factor involved in the development of superior labral anterior to posterior (SLAP) tears in throwing athletes. One of the difficulties inherent to the diagnosis of SLAP tears, especially with regard to imaging studies, is the significant anatomic variability of the biceps anchor-superior labrum complex.

See Also: Biceps Tendonitis

Superior Labral Anatomy

According to Rao et al., there are three predominant variations in superior labral anatomy that may be present in up to 10 % of the general population:

• The sublabral recess: it represents a potential space beneath the biceps anchor and the anterosuperior aspect of the glenoid labrum.
• The sublabral foramen: it is a small orifice located between the anterosuperior labrum and the articular cartilage of the anterior glenoid.
• The Buford complex: it is characterized by an absence of the anterosuperior labrum with a cord-like middle glenohumeral ligament that attaches directly to the superior labrum.

It is crucial for the clinician to identify these findings as normal anatomic variants rather than pathologic lesions since inappropriate “repair” may lead to significant pain and external rotation loss as a result of stiffness.

See Also: Shoulder SLAP Lesion

LHB Course

As the LHB tendon travels obliquely through the joint in an anterolateral direction, the tendon is encased in an outward-facing synovial membrane that is continuous with the joint capsule and renders the tendon extra-synovial. As the tendon travels distally towards the bicipital groove of the proximal humerus, its position is maintained by the capsuloligamentous restraints within the rotator interval.

As the LHB tendon courses towards the bicipital groove, the SGHL and the CHL form a sling around the LHB tendon, primarily preventing its medial subluxation. This sling extends to the most anterior portion of the rotator cable and the biceps reflection pulley (BRP) at the proximal end of the bicipital groove. The BRP, derived from the coalition of the SGHL, CHL, and the upper 1/3 of the subscapularis tendon, redirects the anterolateral course of the LHB tendon such that the tendon travels directly inferiorly along the anterior humeral shaft.

Habermeyer et al. described a 30–40° inferior turn of the Long Head of Biceps Tendon as it exited the joint via the BRP. Tearing of the subscapularis in this region, often known as a “pulley lesion,” can allow medial subluxation of the LHB tendon producing a painful “popping” or “snapping” sensation as the arm is moved. In addition, a biomechanical study by Braun et al. found that the LHB tendon slides up to 18 mm in and out of the joint with forward flexion and internal rotation, respectively. Therefore, the LHB tendon itself is subjected to significant mechanical stresses in the area of the BRP which can lead to tendonitis, tearing or rupture of the LHB.

The bicipital sheath is another complex structure through which the LHB tendon traverses as it passes through the bicipital groove. The floor of this sheath is formed from the coalescence of the SGHL and the subscapularis tendons at the superior aspect of the lesser tuberosity. These fibers then travel laterally, forming the floor of the bicipital sheath. The roof of the sheath is mostly composed of fibers from both the supraspinatus and CHL ligaments. All of these fibers (the floor and the roof of the sheath) combine to form a continuous ring around the LHB tendon as it passes through the bicipital groove thus providing tendon stability.

A recent biomechanical study by Kwon et al. found that the subscapularis tendon was the most important stabilizer of the LHB tendon within the bicipital groove since tears of the subscapularis in this area almost always resulted in medial subluxation of the LHB tendon.

The bony structure of the bicipital groove can also play a role in pathologies of the Long Head of Biceps Tendon. In a radiographic study by Pfahler et al., the opening angle of the groove in patients without LHB tendon pathology was between 101° and 120° with the medial wall having a greater height than the lateral wall. Patients with a shallow groove or a lower medial wall may also be susceptible to subluxation of the LHB tendon.

LHB Vascular Supply

The vascular supply to the LHB tendon near the biceps-labral complex is variably derived from the suprascapular, circumflex scapular and posterior circumflex humeral arteries. Vascularity of the tendon is richest near its origin and dissipates prior to entering the bicipital groove where the tendon is avascular and fibrocartilaginous. This infrastructure helps prevent tendon injury from the sliding action of the LHB within the sheath of the groove.

Similarly, innervation of the Long Head of Biceps Tendon is concentrated near its anchor and dissipates as the tendon travels distally. This arrangement was described as a “net-like” pattern of sympathetic fibers by Alpantaki et al. in a cadaveric study using neurofilament antibodies. In addition, Tosounidis et al. demonstrated the presence of sympathetic α1-adrenergic receptors along the LHB tendon in cadaveric specimens with known acute and chronic shoulder conditions. These studies demonstrate that sympathetic innervation of the proximal LHB tendon may play a role in the pathogenesis of shoulder pain.

Biomechanics

Although the anatomy of the proximal LHB tendon has been well described, its precise function has been debated for many years. The LHB tendon contributed to glenohumeral stability by resisting torsional forces in the abducted and externally rotated position. There is a significantly increased strain applied to the anterior band of the inferior glenohumeral ligament (IGHL) when the biceps-labral complex was detached from its anchor at the superior aspect of the glenoid.

Both the LHB and the short head of the biceps contribute significantly to glenohumeral joint stability, particularly in positions of abduction and external rotation. This contribution to stability was particularly robust after attenuation of anterior stabilizing structures had occurred. Loading of the short head of the biceps alone caused superior migration of the humeral head whereas tensioning of both the short head and the Long Head of Biceps Tendon simultaneously did not result in humeral head translation in any direction.

LHB Tendonitis, Tearing and Rupture

LHB tendonitis can occur as a result of impingement under the coracoacromial arch, subluxation out of the bicipital groove, or attrition as a result of degeneration. Due to the many concurrent pathologies that are typically present in patients with LHB tendonitis, physical diagnosis is often difficult.

However, a precise knowledge of the pathogenesis of LHB tendonitis will help the clinician synthesize a complete and accurate differential diagnosis with an understanding that overlapping conditions are often present.

References

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