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Brachial Plexus Examination

Clinical Examination of the Brachial Plexus by Mr CY Ng


BRACHIAL PLEXUS ANATOMY:

Brachial Plexus Anatomy - Sarah Hart
SEQUENCE (MNEMONIC): Robert Taylor Drinks Cold Beer = Rami, Trunks, Divisions, Cords & Branches


POSITIONS:

  • The roots and trunks lie in the posterior triangle of the neck
  • The divisions are deep to the clavicle 
  • The cords are posterior to the pectoralis minor 
  • Terminal branches begin in the axilla.
ROOTS (5)
  • Are formed by the ventral rami of spinal nerves C5-C8 and T1.
TRUNKS (3)
  • The 5th and 6th cervical roots join to form the upper trunk.
  • The 7th cervical root forms the middle trunk.
  • The 8th cervical and 1st thoracic roots join to form the lower trunk.
DIVISIONS (6)
Each trunk divides into an anterior and a posterior division.

CORDS (3)

  • The three posterior divisions join to form the posterior cord.
  • The anterior divisions of the upper and middle trunk unite to form the lateral cord.
  • The anterior division of the lower trunk continues alone as the medial cord.
BRANCHES
  • Branches come from the rami, the trunks and the cords; usually no branches originate from the divisions.
  • The upper trunk is formed by fusion of ventral rami C5 and C6, therefore it carries nerve fibers from C5 and C6. The middle trunk carries only C7 fibers. The lower trunk carries both C8 and T1 fibers as a result of the fusion of ventral rami of C8 and T1.
  • Since the posterior divisions of all the trunks (upper, middle and lower) join to form the posterior cord, it carries fibers from C5, 6, 7, 8 and T1. The lateral cord is formed from anterior divisions of the upper (C5, 6) and middle (C7) trunks. Therefore, it carries fibers from C5, 6 and 7. The medial cord is formed from the anterior division of only the lower trunk, thus it carries fibers from C8 and T1.
  • The fibers carried in any named branch will be determined by which part of the plexus they originate from and what fibers that particular part is carrying. Any combination of fibers carried in a part can be carried by a branch from that region. (Example: the posterior cord carries C5, 6, 7, 8 and T1 but the axillary nerve carries only C5 and C6 fibers.)
Branches from Roots of the plexus
  • Branch to the phrenic nerve (C5)
  • Dorsal scapular nerve (C5) innervates rhomboideus major and minor and gives a branch to levator scapulae.
  • Long thoracic nerve (nerve to the serratus anterior) (C5,6,7) may be involved in supraclavicular and axillary wounds, neck blows or compression resulting from carrying excess weight on the shoulder. Paralysis of the serratus anterior causes "winging" of the scapula when the arm is flexed and pressed against a fixed object. There is also difficulty in abducting the shoulder above the horizontal position due to a decreased ability to rotate the glenoid fossa upward.
Branches from Trunks
  • Nerve to the subclavius (C5,6) from the upper trunk
  • Suprascapular nerve (C5,6) from the upper trunk innervates supraspinatus and infra-spinatus.
Branches from Divisions
  • Usually none
Branches from Cords
  • Lateral Cord
    • Lateral pectoral nerve (C5,6,7) innervates pectoralis major (clavicular or upper head) and pectoralis minor.
    • Lateral root of the median nerve (C6,7) contributes to the median nerve.
  • Posterior Cord
    • Upper subscapular nerve (C5,6) innervates the upper part of the subscapularis.
    • Thoracodorsal nerve or nerve to the Latissimus dorsi (C5,6,7) innervates the latissimus dorsi.
    • Lower subscapular nerve (C5,6) innervates the lower part of the subscapularis and the teres major.
  • Medial Cord
    • Medial pectoral nerve (C8,T1) innervates pectoralis major and pectoralis minor.
    • Medial cutaneous nerve to the arm (medial brachial cutaneous) (C8,T1) innervates the medial portion of the arm.
    • Medial cutaneous nerve to the forearm (medial antebrachial cutaneous) (C8,T1) innervates the medial half of the forearm.
    • Medial root of the median nerve (C8,T1) contributes to the median nerve.
Terminal Branches (5)
  • Musculocutaneous nerve (C5,6,7)
  • Median nerve (C6,7,8,T1)
  • Ulnar nerve (C8,T1)
  • Radial nerve (C5,6,7,8,T1)
  • Axillary nerve (C5,6)
 *Note that all branches from the medial cord carry C8,T1 fibers, and that the higher spinal segments in the brachial plexus (C5-C6) tend to innervate muscles more proximal on the upper extremity whereas the lower segments (C8,T1) tend to innervate more distal muscles such as those in the hand. (T1).

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