Long Head of Biceps Brachii: Anatomy, Function, Imaging

Topic

Long head of biceps brachii muscle

The long head of the biceps brachii is one of the two proximal heads of the biceps muscle, originating from the supraglenoid tubercle of the scapula and the superior glenoid labrum. It descends through the glenohumeral joint and exits via the bicipital (intertubercular) groove of the humerus enclosed within a synovial sheath.

This slender, tendinous origin makes the long head of the biceps both functionally significant and clinically vulnerable, frequently involved in tendinopathy, instability, and labral injuries such as SLAP (Superior Labrum Anterior to Posterior) lesions.

The long head contributes to shoulder stabilization, assists in elbow flexion and forearm supination, and serves as a dynamic anterior stabilizer of the humeral head during overhead motion.

Synonyms

Long biceps tendon
Long head of the biceps tendon
Intracapsular tendon of the biceps

Origin, Course, and Insertion

Origin:
- From the supraglenoid tubercle of the scapula and adjacent superior glenoid labrum within the shoulder joint capsule.
Course:
- The tendon passes intra-articularly through the shoulder joint, over the humeral head, and under the transverse humeral ligament within the bicipital (intertubercular) groove of the humerus.
- Surrounded by a synovial sheath continuous with the glenohumeral joint cavity.
Insertion:
- Joins the short head of biceps brachii in the mid-arm to form the common biceps tendon, which inserts into the radial tuberosity and gives off the bicipital aponeurosis to the forearm fascia.

Tendon Attachments

Proximal attachment: Supraglenoid tubercle and superior labrum (forms the biceps–labral complex).
Distal course: Lies in the bicipital groove, stabilized by the transverse humeral ligament and subscapularis fibers.
Distal insertion: Into the radial tuberosity (via common tendon).

Relations

Superiorly: Glenohumeral joint capsule and supraspinatus tendon.
Inferiorly: Humeral head and bicipital groove floor.
Medially: Subscapularis tendon near groove entrance.
Laterally: Greater tubercle and pectoralis major tendon.
Anteriorly: Deltoid and coracohumeral ligament.
Posteriorly: Glenoid labrum and joint capsule.

Nerve Supply

Musculocutaneous nerve (C5–C7), branch of the lateral cord of the brachial plexus.

Arterial Supply

Brachial artery and anterior circumflex humeral artery branches supply the tendon and muscle belly.

Venous Drainage

Brachial vein and tributaries of the cephalic vein drain the region.

Function

Elbow flexion: Primary flexor of the forearm at the elbow joint.
Forearm supination: Strong supinator, especially when elbow is flexed.
Shoulder stabilization: Long head tendon acts as a dynamic stabilizer of the humeral head within the glenoid fossa.
Shoulder flexion: Assists in raising the arm forward.
Tension absorber: Reduces anterior and superior translation of the humeral head during motion.

Clinical Significance

Tendinopathy: Overuse inflammation common in athletes and manual laborers.
Instability: Subluxation or dislocation from bicipital groove due to subscapularis or transverse ligament tears.
Rupture: Presents with “Popeye” deformity (muscle retraction); often due to chronic degeneration.
SLAP lesions: Superior labral tears involving the biceps anchor.
Tenosynovitis: Synovial sheath inflammation causing pain in the bicipital groove.
Surgical importance: Biceps tenodesis or tenotomy performed for chronic pain or instability.

MRI Appearance

T1-weighted images:
- Tendon: Low signal (dark), smooth linear structure within bicipital groove.
- Muscle belly: Intermediate signal.
- Marrow: Bright, fatty signal within humeral head and shaft.
- Synovial sheath: Thin low-signal line; mild fluid may appear slightly bright.
- Pathology: Tendinopathy—focal thickening, irregular margins, or intermediate signal intensity.
T2-weighted images:
- Tendon: Low signal, though pathologic changes show hyperintense regions from fluid or inflammation.
- Muscle: Intermediate to slightly darker than T1.
- Fluid: Bright hyperintense signal surrounding tendon in tenosynovitis.
- Labral attachment: SLAP tear shows high-signal cleft between tendon and superior labrum.
STIR:
- Normal tendon: Low-to-intermediate signal.
- Pathologic tendon: Bright hyperintense signal from edema or inflammation.
- Excellent for detecting tenosynovitis, subluxation, and peritendinous edema.
Proton Density Fat-Saturated (PD FS):
- Normal tendon: Uniformly dark, smooth outline in the bicipital groove.
- Abnormal: Bright hyperintense signal indicating tendinopathy or partial tear.
- Complete tear: Discontinuity of tendon fibers with retraction and peritendinous fluid.
T1 Fat-Sat Post-Contrast:
- Normal tendon: Minimal or no enhancement.
- Inflamed tendon sheath: Enhances diffusely in tenosynovitis.
- Postoperative or chronic scarring: Peripheral rim enhancement; non-enhancing fibrotic center.

CT Appearance

Non-Contrast CT:

Tendon: Linear soft-tissue density in the bicipital groove, often difficult to visualize directly.
Bicipital groove: Clear osseous depression between greater and lesser tubercles.
Pathology:
- Calcific tendinitis: Focal high-density deposits along the tendon path.
- Fractures or groove deformity: Well demonstrated on CT bone windows.

Post-Contrast CT (standard):

Enhancement: Normal tendon shows minimal enhancement; inflamed tendon sheath or peritendinous tissue enhances.
Usefulness: Evaluates calcifications, osseous changes, and postoperative anatomy when MRI is contraindicated.

MRI image