Long Head of Triceps Brachii: Anatomy, Function, Imagin

Topic

Long head of triceps brachii muscle

The long head of the triceps brachii is one of the three heads of the triceps muscle located in the posterior compartment of the arm. It arises from the infraglenoid tubercle of the scapula, crosses both the shoulder and elbow joints, and inserts via the common triceps tendon into the olecranon process of the ulna.

As the only head that spans two joints, it plays a critical role in both elbow extension and shoulder stabilization and extension. It assists in adduction of the arm, especially when the arm is abducted, and provides dynamic posterior support to the glenohumeral joint.

This head is anatomically distinct, lying medial to the long head of the biceps and lateral to the teres minor and major muscles, making it an important surgical and imaging landmark in the posterior shoulder.

Synonyms

Long scapular head of triceps
Scapular portion of triceps brachii

Origin, Course, and Insertion

Origin: Infraglenoid tubercle of the scapula.
Course: Descends between the teres minor (above) and teres major (below), then joins the lateral and medial heads of the triceps in the distal third of the arm.
Insertion: Posterior surface of the olecranon process of the ulna via the common triceps tendon.

Tendon Attachments

The proximal tendon is short and strong, arising from the scapula just below the glenoid cavity.
The distal tendon merges with the common triceps tendon, inserting into the olecranon process and blending with the deep fascia of the forearm.

Relations

Anteriorly: Long head of the biceps brachii, posterior capsule of the shoulder joint.
Posteriorly: Deltoid and skin of posterior shoulder.
Superiorly: Teres minor and shoulder joint capsule.
Inferiorly: Teres major and latissimus dorsi.
Medially: Long head of triceps lies adjacent to the axillary nerve and posterior circumflex humeral vessels in the quadrangular space.
Laterally: Lateral head of triceps and radial groove.

Nerve Supply

Radial nerve (C6, C7, C8), branch of the posterior cord of the brachial plexus.

Arterial Supply

Profunda brachii artery (deep brachial artery), via muscular branches.
Additional supply from posterior circumflex humeral artery near its origin.

Venous Drainage

Companion veins of the profunda brachii vein drain into the brachial veins and subsequently the axillary vein.

Function

Elbow extension: Primary extensor of the forearm (acts with medial and lateral heads).
Shoulder extension: Extends the humerus at the glenohumeral joint.
Adduction: Assists latissimus dorsi and teres major in adduction of the arm.
Joint stabilization: Helps resist inferior displacement of the humeral head when the arm is abducted.

Clinical Significance

Tendinopathy: Overuse or repetitive extension (throwing, lifting) may cause proximal tendon inflammation.
Tendon rupture: Rare but occurs at the olecranon insertion or scapular origin, often following trauma or weightlifting.
Entrapment: The axillary nerve or radial nerve may be compressed near the quadrangular space.
Surgical landmark: Defines the quadrangular space (with teres minor, teres major, and humerus) important for axillary nerve exposure.
Imaging relevance: MRI is vital for assessing partial tears, avulsions, and enthesopathy at the infraglenoid tubercle or olecranon insertion.

MRI Appearance

T1-weighted images:
- Muscle belly: Intermediate signal intensity, sharply defined margins.
- Tendon: Low signal (dark); proximal origin visible below the glenoid rim.
- Marrow (scapular or olecranon attachment): Bright fatty signal in normal bone.
- Fatty planes: Bright, providing contrast between muscle and adjacent structures.
- Pathology: Partial tears or chronic atrophy may show focal bright signal within the muscle or tendon thickening.
T2-weighted images:
- Muscle: Intermediate-to-low signal, slightly darker than on T1.
- Tendon: Uniformly low signal in healthy state.
- Pathology: Tendinitis or tear—bright hyperintense areas at the origin, myotendinous junction, or insertion.
- Fluid collections: Hyperintense between muscle and bone in cases of avulsion or hematoma.
STIR:
- Normal muscle: Intermediate-to-dark signal.
- Pathology: Bright hyperintensity indicating edema, strain, or inflammation.
- Sensitive for early myotendinous injuries and enthesitis.
Proton Density Fat-Saturated (PD FS):
- Normal muscle: Intermediate-to-dark, uniform signal.
- Tendinopathy or tear: Focal bright hyperintense signal with peritendinous edema.
- Highlights small partial-thickness tears and subtle myofascial fluid.
T1 Fat-Sat Post-Contrast:
- Normal muscle: Mild homogeneous enhancement.
- Inflamed tendon or enthesis: Focal enhancement at the infraglenoid tubercle or olecranon insertion.
- Chronic scarring or fibrosis: Minimal or peripheral enhancement.
- Avulsion: Enhancing granulation tissue surrounding a low-signal tendon gap.

CT Appearance

Non-Contrast CT:

Muscle: Homogeneous soft-tissue density in posterior arm.
Tendon: Linear dense band inserting onto olecranon process.
Bone attachments: Infraglenoid tubercle and olecranon clearly visible.
Pathology: Detects avulsion fractures, calcific tendinopathy, or enthesophyte formation.
Useful for postoperative evaluation and calcified lesions within tendon or myotendinous junction.

Post-Contrast CT (standard):

Muscle: Homogeneous enhancement.
Inflamed tendon or surrounding tissue: Focal enhancement in tendinitis or healing tears.
Valuable for assessing hematomas, chronic scarring, and soft-tissue masses adjacent to the triceps.

MRI image