The medial head of the triceps is the deepest and smallest head, arising from the posterior humeral surface below the radial groove. It is the primary elbow extensor at low loads and speeds, with the long and lateral heads recruited for higher force requirements. The medial head is often preserved in radial nerve palsy at the spiral groove because some of its supply comes from branches given off proximal to the groove.
| Origin | Posterior humeral surface below the radial groove (entire posterior surface below the spiral groove) |
|---|---|
| Insertion | Olecranon via the triceps tendon |
| Nerve Supply | Radial nerve (C7, C8) |
| Blood Supply | Profunda brachii artery |
| Actions | Elbow extension — the primary steady-state extensor, active throughout the extension range |
|---|
Because the medial head arises below the radial groove, a portion of its nerve supply comes from radial nerve branches given off before the spiral groove — explaining why the medial head (and a strip of elbow extension) may be preserved in some radial groove level palsies.
Cubital tunnel syndrome (ulnar nerve at the elbow) can be confused with lower radial nerve palsy, but the medial head of triceps is innervated by the radial nerve and is preserved in cubital tunnel syndrome (ulnar nerve), while weak elbow extension indicates radial nerve involvement.
The medial head is palpable deep to the long head on the posteromedial arm, becoming firm during elbow extension against resistance.
Olecranon avulsion of the triceps tendon producing inability to extend the elbow against gravity requiring surgical repair.
