The medial head is the most deeply placed and most consistently active of the three triceps heads. Its distal radial nerve supply means it is spared in mid-humeral radial nerve palsy (the "wrist drop" injury at the spiral groove).
| Origin | Posterior humerus — below the spiral groove on the medial side |
|---|---|
| Insertion | Posterior olecranon via the common tendon |
| Nerve Supply | Radial nerve (C6, C7, C8) — branches arising distal to the spiral groove |
| Blood Supply | Deep brachial artery |
| Actions | Extends the elbow — active through the full range of extension; The deepest and most tonically active head — remains active even during gentle elbow extension |
|---|
The medial head's distal radial nerve supply (below the spiral groove) means it is tested in radial nerve injury localisation — preserved medial head (elbow extension) with absent brachioradialis (proximal radial nerve) indicates an injury above the brachioradialis branch. The anconeus (which shares the elbow extension function) also has a distal radial nerve supply.
Palpated as the deep medial posterior arm muscle during gentle resisted elbow extension.
Preserved medial head elbow extension despite wrist drop in spiral groove radial nerve palsy, localising the lesion to the mid-humerus distal to the medial head branches.
