Pronator Teres Innervation
The pronator teres muscle is innervated by the median nerve, which arises from nerve roots C6 and C7.
Anatomical Pathway
The median nerve that supplies the pronator teres originates from the brachial plexus, specifically formed by contributions from the C6 and C7 nerve roots 1. These nerve roots pass between the anterior and middle scalene muscles with the subclavian artery to form the trunks of the brachial plexus 1. The trunks then split into anterior and posterior divisions, form cords, and the median nerve ultimately travels into the forearm to innervate the pronator teres muscle 1.
Clinical Anatomy and Variations
The median nerve typically passes between the humeral and ulnar heads of the pronator teres muscle in approximately 74% of cases, while in 26% of cases it passes under the muscle 2. The ulnar head of the pronator teres is present in 86% of limbs 2.
The median nerve most commonly provides two motor branches to the pronator teres muscle (66% of cases) 2. The first branch from the median nerve to the forearm flexor muscle group typically includes the pronator teres muscle branch, along with branches to the flexor carpi radialis and portions of the flexor digitorum superficialis 3.
Anatomical Variations and Clinical Significance
Several important anatomical variations exist:
- In 72% of cases, the humeral head originates from both the medial humeral epicondyle and medial intermuscular septum, while in other cases it originates only from the medial epicondyle 2
- The ulnar head may be fibromuscular (53.6%), purely muscular (20.5%), a fibrotic band (16.1%), absent (8%), or have two arches (1.8%) 4
- In 71.5% of forearms, the ulnar head is either fibromuscular or a fibrotic band, which has implications for median nerve compression 4
These variations are clinically significant because the median nerve can become entrapped as it passes through or near the pronator teres muscle, causing pronator syndrome 2, 4, 5. The most reliable diagnostic sign is "pronation-pain" produced by passive supination of the wrist or active pronation against resistance 5.