Brachial Plexus

Authors

Affiliations

Nathaniel Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Brachial Plexus¹

Brachial Plexus²

Anatomy

Nerve roots

The anterior divisions of 5 nerve roots compose the brachial plexus:

1. C5
2. C6
3. C7
4. C8
5. T1

Trunks

The brachial plexus nerve roots become 3 trunks:

1. Superior Trunk (C5, C6)²
2. Middle Trunk (C7)²
3. Inferior Trunk (C8, T1)²

Superior Trunk

• Nerve to Subclavius (C5, C6) originates from the Superior Trunk²
• The suprascapular nerve (C5, C6) originates from the Superior Trunk at Erb’s point².

Divisions

6 divisions are formed from the 3 trunks:

1. Anterior Division of the Superior Trunk
2. Posterior Division of the Superior Trunk
3. Anterior Division of the Middle Trunk
4. Posterior Division of the Middle Trunk
5. Anterior Division of the Inferior Trunk
6. Posterior Division of the Inferior Trunk

Cords

The divisions then combine to form 3 cords:

1. Lateral cord
2. Posterior cord
3. Medial cord

Note

These three cords are named for their geographical relationship to the axillary artery²

The medial and lateral pectoral nerves extend from the medial and lateral cords, respectively (see Fig. 3-9). They supply the pectoralis major and pectoralis minor muscles. The pectoralis major muscle has dual innervation.1 The lateral pectoral nerve (C5–7), which is more medial in the muscle, travels with the thoracoacromial vessels, and innervates the clavicular and sternal heads. The medial pectoral nerve (C8–T1) shares a course with the lateral thoracic vessels and provides innervation to the sternal and costal heads.1 The main trunk of these nerves can be found near the origin of the vascular supply of the muscle.

The thoracodorsal nerve, or middle subscapular nerve, which arises from the posterior cord of the brachial plexus with its motor fiber contributions from C6, C7, and C8 (see Fig. 3-9). This nerve courses along the posterior–lateral chest wall, along the surface of the serratus anterior, and deep to the subscapularis, giving rise to branches that supply the latissimus dorsi. ■ The lower subscapular nerve (C5–6) to the teres major and part of the subscapularis muscle (see Fig. 3-9). ■ Sensory branches of the medial cord (C8–T1 or T1 alone) comprise the medial cutaneous (antebrachial) nerve to the medial surface of the forearm and the medial cutaneous (brachial) nerve to the medial surface of the arm (see Fig. 3-9).1

Lateral Cord

• Contributions to the Medial Pectoral Nerve (C8, T1)²
• Contributions to the Lateral Pectoral Nerve (C5, C6, C7)²

Posterior Cord

• Upper Subscapular Nerve (C5, C6)²
• Thoracodorsal Nerve (Middle Subscapular Nerve) (C6, C6, C7, & C8)²
• Lower Subscapular Nerve (C5, C6)²

Medial Cord

• Contributions to the Medial Pectoral Nerve (C8, T1)²
• Contributions to the Lateral Pectoral Nerve (C5, C6, C7)²
• Medial cutaneous nerve of the arm (?var:ref-medial-cutaneous-nerve-of-the-arm.roots)²
• Medial cutaneous nerve of the forearm (?var:ref-medial-cutaneous-nerve-of-the-forearm.roots)²

Branches

1. Musculocutaneous nerve (C5, C6, C7)
2. Axillary nerve (C5, C6)
3. Radial nerve (C5, C6, C7, C8, T1)
4. Musculocutaneous nerve (C5, C6, C7)
5. Musculocutaneous nerve (C5, C6, C7)

Traumatic Injury

Traumatic injuries to the brachial plexus typically involve a combination of different injuries:²

1. Compression of spinal nerves²
2. Traction injuries of spinal roots and nerves²
3. Avulsions of spinal roots²

Note

If the rootlets are disconnected from the spinal cord via trauma, they generally exit the intradural space, but in some rare cases they can remain in the space²

Obstetric Lesions

The main cause of brachial plexus injuries are due to difficulties during childbirth².

Obstetric brachial plexus palsy is usually caused by stretch (neurapraxia or axonotmesis) and incomplete rupture more often than complete rupture or avulsion².

Upper Obstetrical Brachial Palsy

• Upper Obstetrical brachial palsy involves C5, C6, and usually C7 Nerve roots².
• Upper obstetrical brachial palsy is also called “Erb’s Palsy”²
• The majority of cases of obstetric brachial plexus palsy involve “Erb’s Palsy”².
• Erb’s Palsy lesions are always supraclavicular².

Lower Obstetrical Brachial Palsy

• Lower Obstetrical brachial palsy predominantly involves C8 and T1 nerve roots².
• Lower OBstetrical Brachial palsy is a rare birth injury²
• Lower Obstetrical brachial palsy is also known as “Klumpke’s Palsy” or “Dejerine-Klumpke Palsy”²

Total Obstetrical Brachial Palsy

Total Obstetrical brachial palsy predominantly involves C5, C6, C7, C8 and T1 nerve roots².

“Klumpke’s paralysis is characterized by paralysis and atrophy of the small hand muscles and flexors of the wrist (the so-called claw-hand). Prognosis of this type is more favorable. If the sympathetic rami of T1 are involved, Horner syndrome (ptosis, enophthalmos, facial reddening, and anhydrosis) may be present.25”²

Dysfunction

Brachial Plexus irritation

Tests and measures

• Stretch test
• Cervical Rotation Lateral Flexion Test
• Tinel’s Sign

References

1.

Gilroy AM, MacPherson BR, Wikenheiser JC, Voll MM, Wesker K, Schünke M, eds. Atlas of Anatomy. 4th ed. Thieme; 2020.

2.

Dutton M. Dutton’s Orthopaedic Examination, Evaluation, and Intervention. 5th ed. McGraw Hill Education; 2020.