Triceps Brachii Anatomy: Three Heads, Origins, Insertion, Nerve Supply & Clinical Relevance

The triceps brachii is the large three-headed muscle on the posterior arm, the primary extensor of the elbow joint. Understanding its anatomy is essential for clinical examination, surgical approaches, and rehabilitation.

Origins (Proximal Attachments)

Head	Origin
Long head	Infraglenoid tubercle of the scapula (intra-articular, extrasynovial)
Lateral head	Posterior humerus, superior to radial groove (linear ridge)
Medial head	Posterior humerus, inferior to radial groove (broad, deep)

Insertion (Distal Attachment)

• Common tendon inserts on the olecranon process of the ulna.
• Also blends with antebrachial fascia (deep fascia of forearm).

Key Anatomical Relations

• Radial nerve spirals in radial groove between lateral and medial heads.
• Long head crosses shoulder joint → assists shoulder extension/adduction.
• Medial head is the "workhorse" — active in all elbow extension.
• Lateral head recruited for high-force extension.

Innervation & Blood Supply

• Radial nerve (C6–C8).
• Deep brachial artery (profunda brachii).

Clinical Relevance

• Radial nerve injury at spiral groove → wrist drop (triceps spared — proximal innervation).
• Triceps tendon rupture: rare; mechanism: forced flexion on contracted muscle.
• EMG: distinguishes C7 radiculopathy vs. radial neuropathy.