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Triceps brachii muscle

The triceps brachii is the large, three-headed muscle occupying the entire posterior compartment of the arm. It is the primary extensor of the elbow joint, acting as a powerful antagonist to the biceps brachii and brachialis. The triceps also assists in shoulder extension and adduction via its long head.

The muscle consists of three heads — long, lateral, and medial — which converge into a common tendon inserting onto the olecranon process of the ulna. The triceps brachii plays a key role in pushing, throwing, and weight-bearing activities of the upper limb.

Synonyms

  • Triceps muscle of arm

  • Extensor of elbow

Origin, Course, and Insertion

  • Long head: Infraglenoid tubercle of the scapula

  • Lateral head: Posterior surface of the humerus above the radial (spiral) groove

  • Medial head: Posterior surface of the humerus below the radial groove and medial intermuscular septum

  • Course: Fibers of all three heads converge inferiorly to form a broad, flat tendon inserting onto the olecranon process of the ulna

  • Insertion: Posterior surface of the olecranon process of ulna, and via an aponeurosis to the deep fascia of the forearm

Tendon Attachments

  • Common tendon blends with olecranon periosteum and joint capsule of the elbow

  • Occasionally, small slips attach to the fascia of the anconeus or posterior capsule

  • The distal tendon passes superficial to the ulnar nerve near the medial epicondyle, a site relevant for surgical and imaging evaluation

Relations

  • Anteriorly: Humerus, radial nerve, and profunda brachii vessels in the spiral groove

  • Posteriorly: Deep fascia and skin of posterior arm

  • Medially: Ulnar nerve and medial intermuscular septum

  • Laterally: Lateral intermuscular septum and deltoid insertion

  • Inferiorly: Olecranon and anconeus muscle

Nerve Supply

  • Radial nerve (C6–C8) — supplies all three heads through separate branches

  • The long head receives an additional branch near the axilla

Arterial Supply

  • Profunda brachii artery (deep brachial artery)

  • Posterior circumflex humeral artery (long head region)

  • Superior ulnar collateral artery (distal portion)

Venous Drainage

  • Venae comitantes of profunda brachii and collateral arteries, draining into the brachial vein

Function

  • Elbow extension: Primary extensor of forearm at elbow joint

  • Shoulder extension: Long head assists in extending the humerus at the shoulder

  • Adduction: Long head aids in adduction of the arm at the shoulder joint

  • Joint stability: Prevents posterior displacement of the humerus during load-bearing activities

Clinical Significance

  • Triceps tendinopathy: Overuse or strain, especially in throwing athletes and weightlifters

  • Tendon rupture: Usually near olecranon insertion; causes loss of active elbow extension

  • Radial nerve injury: Leads to triceps weakness or paralysis, depending on lesion level

  • Avulsion fractures: May occur at the olecranon attachment site

  • Bursitis: Olecranon bursa inflammation can mimic triceps insertional pain

  • Imaging relevance: MRI and CT essential for detecting tendon tears, muscular edema, and post-traumatic changes

MRI Appearance

  • T1-weighted images:

    • Muscle: Intermediate signal intensity with clear fascicular pattern

    • Tendon: Low signal (dark), continuous with olecranon insertion

    • Marrow (olecranon): Bright (fatty)

    • Fat planes: Bright and sharply defined around muscle

    • Tear or hematoma: Intermediate-to-bright localized signal disrupting tendon continuity

  • T2-weighted images:

    • Normal muscle: Intermediate-to-low signal, slightly darker than T1

    • Tendon: Very low signal; appears as dark linear band

    • Pathology: Hyperintense signal in tendon or muscle fibers in partial or full-thickness tears

    • Inflammation/edema: Bright signal in peritendinous fat or myotendinous junction

  • STIR:

    • Normal muscle: Intermediate-to-dark signal intensity

    • Pathology: Bright hyperintense areas in muscle belly or tendon (strain, edema, or inflammation)

    • Excellent for detecting early or subtle muscle injury

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: Intermediate-to-dark homogeneous signal

    • Abnormal: Bright hyperintense signal within tendon or myotendinous junction (partial tear, tendinitis)

    • Accurately shows fluid around olecranon bursa or triceps tendon sheath

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: Mild uniform enhancement

    • Tendinitis or inflammation: Focal or diffuse enhancement along tendon or myotendinous junction

    • Chronic tear or fibrosis: Peripheral rim enhancement with central low-signal fibrosis

CT Appearance

Non-Contrast CT:

  • Muscle: Homogeneous soft-tissue density in posterior arm

  • Tendon: Thin dense structure inserting on olecranon

  • Olecranon: High-density cortical bone, clearly visualized

  • Pathology: Detects tendon calcification, enthesophytes, avulsion fragments, and hematoma

  • Excellent for fracture or postoperative evaluation

Post-Contrast CT (standard):

  • Muscle: Homogeneous enhancement

  • Inflammatory or vascular lesions: Focal or diffuse enhancement of peritendinous tissues

  • Useful for assessing post-surgical scarring, infection, or neoplastic infiltration

MRI image

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Triceps brachii muscle sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

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Triceps brachii muscle CT axial image