Triceps Brachii Tendon: Anatomy, Function, Imaging

Topic

Triceps brachii tendon

The triceps brachii tendon is the strong, conjoined terminal tendon of the triceps brachii muscle, the primary extensor of the elbow. It forms near the distal third of the posterior arm as the three muscular heads (long, lateral, and medial) converge into a single thick tendon that inserts onto the olecranon process of the ulna.

This tendon provides the final power for elbow extension and transmits force generated by the triceps to the forearm. It is one of the strongest tendons in the upper limb but may be injured in direct trauma, avulsion, or overuse conditions, especially in athletes or after sudden resisted flexion.

Synonyms

Common tendon of triceps brachii
Triceps tendon insertion

Origin, Course, and Insertion

Origin: Formed by the convergence of the tendinous fibers of the long, lateral, and medial heads of the triceps brachii muscle.
Course:
- Runs downward posterior to the elbow joint.
- Becomes a thick, flattened tendon above the olecranon.
- Passes superficial to the posterior capsule of the elbow joint, separated by the subtendinous olecranon bursa.
Insertion:
- Attaches to the posterior surface and upper margin of the olecranon process of the ulna.
- Some fibers extend into the deep fascia of the forearm and the posterior elbow capsule (forming the “tricipital expansion”).

Tendon Attachments

Primary attachment: Olecranon process of the ulna.
Secondary expansions: Lateral margin of the olecranon and deep fascia of the forearm.
Accessory fibers: Blend with posterior capsule, stabilizing the elbow.

Relations

Anteriorly: Elbow joint capsule and olecranon fossa of humerus.
Posteriorly: Subcutaneous olecranon bursa and skin of the posterior elbow.
Laterally: Anconeus muscle and lateral intermuscular septum.
Medially: Ulnar nerve and posterior ulnar recurrent artery (deep).
Superiorly: Triceps brachii muscle bellies.
Inferiorly: Posterior border of ulna and fascia of the forearm.

Nerve Supply

The tendon itself has no direct motor innervation, but the triceps brachii muscle is supplied by the radial nerve (C6–C8), which indirectly influences tendon function through muscle contraction.

Arterial Supply

Deep brachial (profunda brachii) artery, via collateral branches near the elbow.
Superior ulnar collateral artery contributes to the peritendinous vascular plexus.

Function

Elbow extension: Primary tendon transmitting force for elbow extension.
Joint stabilization: Prevents posterior displacement of the forearm during load bearing.
Force transmission: Converts muscle contraction into linear force for movement and stabilization.
Synergistic action: Assists shoulder extension via the long head of the triceps.

Clinical Significance

Tendinopathy: Common in weightlifters, throwers, or after repetitive extension activities.
Partial tear: Typically occurs at the myotendinous junction or insertion on the olecranon.
Complete rupture: Often results from sudden eccentric contraction; presents with swelling, pain, and loss of elbow extension.
Olecranon avulsion: May include bony fragment with tendon attachment.
Surgical relevance: Requires prompt repair; delayed treatment leads to weakness and deformity.
Bursitis association: Chronic friction over the olecranon can cause inflammation of the subtendinous or subcutaneous bursa.

MRI Appearance

T1-weighted images:
- Tendon: Low signal (dark), uniform thickness inserting onto olecranon.
- Muscle belly: Intermediate signal.
- Peritendinous fat: Bright, enhancing contrast with dark tendon.
- Tear: Partial or complete discontinuity with intermediate-to-bright signal in defect.
- Chronic tendinopathy: Irregular thickening with interspersed intermediate signal.
T2-weighted images:
- Normal tendon: Low signal (dark) with clear margins.
- Muscle belly: Intermediate signal, slightly darker than on T1.
- Partial tear or tendinopathy: Bright hyperintense signal within or around tendon fibers.
- Complete tear: Gap filled with hyperintense fluid or hematoma between retracted tendon ends.
- Inflammation: Peritendinous edema with surrounding bright signal.
STIR:
- Normal tendon: Intermediate-to-dark signal.
- Tendinitis or partial tear: Bright hyperintense signal outlining or infiltrating tendon substance.
- Soft-tissue edema: Diffuse bright signal in surrounding fat or muscle.
Proton Density Fat-Saturated (PD FS):
- Normal tendon: Uniformly dark and well defined.
- Pathology: Bright hyperintense streaks or foci within tendon or near insertion, representing edema or microtears.
- Ideal for detecting: Partial tears, enthesitis, or post-surgical scar.
T1 Fat-Sat Post-Contrast:
- Normal tendon: Minimal or no enhancement.
- Inflamed or reactive tendon: Peripheral linear enhancement along insertion.
- Chronic tendinopathy: Heterogeneous enhancement due to neovascularization.
- Postoperative repair: Granulation tissue appears enhancing around the repair site.

CT Appearance

Non-Contrast CT:

Tendon: Seen as soft-tissue density band inserting on the olecranon.
Bone: High attenuation olecranon cortex with smooth tendon attachment.
Pathology:
- Calcific tendinitis shows focal hyperdense deposits within the tendon.
- Avulsion fracture shows displaced or comminuted bone fragments at the olecranon tip.
- Chronic changes: enthesophytes or cortical irregularity.

Post-Contrast CT (standard):

Normal tendon: Mild uniform enhancement of peritendinous tissue.
Inflammation or repair: Enhanced thickened tissue around insertion site.
Complete rupture: Fluid or enhancing soft-tissue gap between tendon and bone.
Usefulness: Excellent for detecting calcifications, ossifications, and bone avulsions not well seen on MRI.

MRI images

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