Pronators (Pronator Teres and Pronator Quadratus)
Two pronator muscles of the forearm; both supplied by the median nerve.
Pronator Teres
| Feature | Detail |
|---|---|
| Humeral head | Medial epicondyle (common flexor origin) |
| Ulnar head | Medial border of coronoid process |
| Insertion | Middle of lateral shaft of radius |
| Nerve supply | Median nerve |
| Action | Pronation |
Key relation: Median nerve passes between the two heads as it enters the forearm from the cubital fossa. Pronator teres = medial boundary of cubital fossa.
Pronator Quadratus
| Feature | Detail |
|---|---|
| Origin | Oblique ridge on lower 1/4 of anterior ulna |
| Insertion (superficial fibres) | Lower 1/4 of anterior surface + anterior border of radius |
| Insertion (deep fibres) | Triangular area above ulnar notch of radius |
| Nerve supply | Anterior interosseous nerve (branch of median nerve, C8-T1) |
Actions
| Muscle | Action |
|---|---|
| Pronator teres | Pronates forearm |
| Pronator quadratus (superficial) | Prime mover of pronation |
| Pronator quadratus (deep) | Stabilises inferior radio-ulnar joint |
Applied Anatomy
- Median nerve compression — between two heads of pronator teres in proximal forearm; part of median nerve entrapment spectrum at elbow
- AIN syndrome — AIN supplies pronator quadratus + FPL + lateral half of FDP; AIN injury → weakened pronation (more evident against resistance, as PT partially compensates) + loss of FPL + lateral FDP function
The forearm has two pronator muscles — pronator teres (proximal, superficial) and pronator quadratus (distal, deep) — both supplied by the median nerve (directly, or via its anterior interosseous branch).
Pronator Teres
| Feature | Detail |
|---|---|
| Humeral head | Medial epicondyle of the humerus (common flexor origin) |
| Ulnar head | Medial border of the coronoid process of the ulna |
| Insertion | Middle of the lateral aspect of the shaft of the radius |
| Nerve supply | Median nerve |
| Action | Pronation of the forearm |
Key relation: The median nerve passes between the humeral and ulnar heads of pronator teres as it enters the forearm from the cubital fossa. Pronator teres forms the medial boundary of the cubital fossa.
Pronator Quadratus
| Feature | Detail |
|---|---|
| Origin | Oblique ridge on the lower one-fourth of the anterior surface of the shaft of the ulna, and the area medial to it |
| Insertion (superficial fibres) | Lower one-fourth of the anterior surface and the anterior border of the radius |
| Insertion (deep fibres) | Triangular area above the ulnar notch of the radius |
| Nerve supply | Anterior interosseous nerve (branch of median nerve, C8-T1) |
Actions
| Muscle | Action |
|---|---|
| Pronator teres | Pronates the forearm |
| Pronator quadratus (superficial fibres) | Pronates the forearm — the prime mover for pronation |
| Pronator quadratus (deep fibres) | Bind the lower ends of the radius and ulna together, stabilising the inferior radio-ulnar joint |
Pronator quadratus acts throughout pronation as a deep stabiliser of the radio-ulnar joints, while pronator teres assists, particularly against resistance and in quick movements.
Applied Anatomy
- Median nerve compression may occur as it passes between the two heads of pronator teres in the forearm — part of the spectrum of median nerve entrapment neuropathies at the elbow/proximal forearm (see Applied Anatomy of Median Nerve).
- Anterior interosseous nerve (AIN) syndrome: Since pronator quadratus is supplied by the AIN (along with flexor pollicis longus and the lateral half of flexor digitorum profundus), AIN injury weakens pronation (more evident with the forearm pronated against resistance, since pronator teres can still partially compensate) — see Branches of Median Nerve and Applied Anatomy of Median Nerve for the full AIN syndrome picture.
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