Muscles Innervated by the C6 Nerve Root
The C6 nerve root primarily innervates muscles of the upper limb involved in elbow flexion, forearm pronation, and wrist extension. The muscles innervated by the C6 nerve root include the biceps brachii, brachialis, brachioradialis, pronator teres, extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB).
Primary C6 Innervated Muscles
- Biceps brachii - A primary elbow flexor that is predominantly innervated by C5 and C6 1
- Brachialis - Another elbow flexor muscle with significant C6 innervation 2, 1
- Brachioradialis - Functions in elbow flexion and is predominantly supplied by C6 1
- Pronator teres - Responsible for forearm pronation with dominant innervation from C6, though it may also receive some C7 innervation 1
- Wrist extensors - Specifically the extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB), which are predominantly supplied by C6 3, 1
Clinical Significance
Understanding C6 innervation patterns is crucial for:
- Diagnosing radiculopathies - In C6 radiculopathy, weakness is most commonly observed in forearm pronation (72% of cases), which is twice as common as wrist extension weakness 3
- Neurological examination - Testing these muscle groups helps localize lesions to specific nerve roots 1
- Surgical planning - For procedures such as nerve transfers in cases of brachial plexus injuries involving C6 2, 4
Anatomical Pathway
The C6 nerve root forms part of the brachial plexus, which is structured as follows:
- The C6 ventral ramus, along with C5-T1, forms the brachial plexus 5
- The nerve roots pass between the anterior and middle scalene muscles with the subclavian artery to form the trunks 5
- Trunks then split into anterior and posterior divisions, form cords, and travel with the subclavian artery and vein 5
- Terminal branches continue into the arm and forearm to innervate the respective muscles 5
Clinical Assessment of C6 Function
When evaluating C6 nerve root function, the following tests are most valuable:
- Forearm pronation strength - The most sensitive indicator of C6 radiculopathy 3, 1
- Elbow flexion strength - Testing biceps and brachialis function 1
- Wrist extension strength - Testing ECRL and ECRB function 3, 1
Common Pitfalls in Assessment
- Overlooking pronator teres weakness - This is the most frequent motor finding in C6 radiculopathies but is often not routinely tested 3
- Confusing radiculopathy with plexopathy - Pain that radiates in a dermatomal distribution with or without accompanying sensory or motor loss reflects radiculopathy, while symptoms in multiple peripheral nerve distributions suggest plexopathy 5
- Incomplete testing - Failure to test all C6-innervated muscles may lead to missed diagnoses 3, 1
Understanding these innervation patterns is essential for accurate diagnosis and treatment of conditions affecting the C6 nerve root, including radiculopathies, brachial plexus injuries, and cervical spondylosis.