Medial cord !
The medial cord of the brachial plexus lies in the armpit on the inner side of the axillary artery; it gives the ulnar nerve and part of the median nerve.
Official name: Medial cord of the brachial plexus
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What it is
The inner bundle of the plexus beside the axillary artery.
What it does
Gives the ulnar nerve and part of the median nerve.
Key facts
- Roots
- C8–T1 (anterior division of the inferior trunk)
- Moves
- Medial pectoral nerve, ulnar nerve, medial root of the median nerve
- Feeling from
- Medial cutaneous nerves of the arm and forearm
Relations
- Course
- The continuation of the anterior division of the lower trunk; it lies first behind the first part of the axillary artery, then medial to the second part, and divides at the lower border of pectoralis minor into the ulnar nerve and the medial root of the median nerve
- In front
- Pectoralis minor, which its medial pectoral branch pierces
- Lateral
- The axillary artery (second part)
- Medial
- The axillary vein, with the lateral group of axillary lymph nodes along it
- Behind
- Subscapularis on the posterior wall of the axilla
How to find it
Deep to pectoralis minor, between the axillary artery and the axillary vein. On infraclavicular ultrasound it is the most medial cord, often partly behind the artery; in a dissection it is traced up the medial limb of the 'M' from the ulnar nerve.
Examination
- Resisted index abduction (first dorsal interosseous) and thumb palmar abduction (abductor pollicis brevis): weakness of both, ulnar and median muscles, places the lesion above the elbow at the medial cord, lower trunk or C8–T1
- Pinprick on the medial arm and medial forearm: loss supports a medial cord or lower trunk lesion
- Froment's sign and clawing of the ring and little fingers show the ulnar component
On imaging
On infraclavicular ultrasound and sagittal MRI it lies medial to the second part of the axillary artery, often between artery and vein. MRI is the main plexus test. An apical lung tumour (Pancoast) involves the lower trunk and medial cord: a chest radiograph may show it, and MRI best shows plexus invasion. Radiographs or CT also show a cervical rib.
Common problems
- Stretch injuries from motorcycle crashes or falls that force the head and shoulder apart.
- Birth injury (Erb's palsy) affecting the upper trunk: the arm hangs turned inward ('waiter's tip').
- Compression at the thoracic outlet between the collarbone and the first rib.
How it is diagnosed
A detailed exam of strength and feeling in each nerve's area. MRI, EMG and nerve conduction studies show the level and severity.
Treatment
- Physical therapy and watching for recovery; many stretch injuries improve.
- Nerve repair, graft or nerve transfer surgery for injuries that do not recover, ideally within months.
Clinical notes
- Infraclavicular trauma and axillary surgery can injure it together with the axillary vein
- Pancoast tumour and neurogenic thoracic outlet syndrome give a similar picture from the lower trunk; Horner syndrome (T1 root) and supraclavicular signs point above the cords
- Nerve conduction: an abnormal medial antebrachial cutaneous sensory response with abnormal ulnar and thenar motor responses localises to the medial cord or lower trunk
Anatomical variants
- The medial and lateral roots may join low in the arm, so the median nerve forms below the axilla
- Prefixed or postfixed plexuses shift its root content up (C7–C8) or down (T1–T2)
Development
It comes from the anterior division of the lower trunk (C8–T1), the segments of the postaxial (ulnar) border of the limb bud; hence its share of the ulnar side of the flexor compartment, the intrinsic hand muscles and the skin of the medial arm and forearm.
Memory aid
Medial cord branches, 'M4U': Medial pectoral, Medial cutaneous of the arm, Medial cutaneous of the forearm, Medial root of the median nerve, Ulnar nerve.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Which roots form the medial cord of the brachial plexus, and which motor fibres does it carry?
C8–T1 from the lower trunk; it carries the motor fibres for all the small hand muscles, ulnar and thenar alike.
What separates a medial cord lesion from an ulnar nerve lesion at the elbow?
Medial forearm numbness: the medial cord gives the medial cutaneous nerve of the forearm, which an ulnar lesion at the elbow spares.
Between which two structures does the medial cord of the brachial plexus lie in the axilla?
Between the second part of the axillary artery (lateral) and the axillary vein (medial), behind pectoralis minor.
Educational information, not medical advice. For any symptom, see a health professional.
Its names
- Official Latin (TA2)
- fasciculus medialis plexus brachialis TA2 6417
- Official Spanish (DeCS)
- Fascículo medial del plexo braquial
- English (TA2)
- Medial cord of the brachial plexus
Related
Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb, Brachial Plexus; Anatomy, Head and Neck: Brachial Plexus; Anatomy of the Human Body (20th ed.): The Branchial Region (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.
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Representative model, for educational purposes only.
