Updated: 10/27/2020

Brachial Plexus

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Topic
Overview
 

 
Introduction
  • Standard: C5, C6, C7, C8, T1 – 77% of patients
  • Prefixed: Prefixed (contributions from C3, C4) – 22% 
  • Postfixed (roots caudal to T1) – 1%
COMPOSITION: “Robert Turner Drinks Cold Beer”
  • Roots (5):  ventral rami of C5-T1, superior and posterior to subclavian
    • dorsal scapular nerve (C5): through levator scapula to supply levator scapula, rhomboid major & minor
    •  long thoracic nerve (C5, 6, 7): posterior to plexus onto thoracic wall to supply serratus anterior
  • Trunks (3): emerge from triangle formed by anterior scalene, middle scalene, first rib
    • superior (C5,6 roots)
      • suprascapular nerve (C5, 6): through suprascapular notch to supraspinatus, infraspinatus, AC and glenohumeral joints
      • nerve to subclavius (C5, 6)
      • Erb's palsy 
        • tear of upper trunk (C5-C6 roots) that is usually caused by traction during delivery or trauma later in life
        • leads to difficulty with abduction, lateral rotation, and flexion/supination
    • middle (C7)
    • inferior (C8, T1)
  • Divisions (6): 3 anterior, 3 posterior (each trunk gives 1 anterior and 1 posterior division)
  • Cords (3):
    • Posterior Cord:  formed from 3 posterior division
      •  upper subscapular nerve (C5, 6):  subscapularis
      •  lower subscapular nerve (C5,6):  subscapularis, teres major           
      •  thoracodorsal nerve (C6, 7, 8):  latissmus dorsi
    •  Lateral Cord:  ant divisions of superior & middle trunks (C5, 6, 7)
      • lateral pectoral nerve (C5, 6, 7):  supplies medial aspect of pectoralis major, communication with medial pectoral nerve
    • Medial Cord:  anterior division of inferior trunk (C8, T1)
      • medial pectoral nerve (C8, T1): pierces pec minor; supplies pec minor and lateral aspect of pec major
      • medial brachial cutaneous nerve (T1)
      • medial antebrachial cutaneous nerve (C8, T1)
      Branches (6) – 2 terminal branches from each cord
      • Posterior cord:
        • axillary nerve (C5, 6):  through quadrilateral space to teres minor, deltoid, major nerve supply to glenohumeral joint, superior lateral brachial cutaneous nerve
        • radial nerve (C5 – T1): runs with long head of triceps (triangular space) into radial groove on posterior humerus; supplies elbow & forearm extensors,  supinator; posterior brachial cutaneous, inferior lateral brachial cutaneous, posterior antebrachial cutaneous, superficial radial (post. radial hand)
      • Lateral cord:              
        • lateral cord of median nerve (C5 – C7): joins medial cord anterior to axillary artery then travels with artery: wrist flexors (except FCU, ulnar ½ FDP), pronators, radial two lumbricals, OP, APB, superficial head FPB); sensory distribution in hand 
        • musculocutaneous (C5, 6, 7):  most superficial branch, pierces coracobrachialis (1.5-9 cm from origin) to supply biceps, coracobrachialis, brachialis, ends as lateral antebrachial cutaneous nerve 
      • Medial cord:   
        • medial cord of median nerve (C8, T1):  see above
        • ulnar nerve (C8, T1) :  FCU, ½ FDP, adductor pollicus, deep head FPB, hypothenar, intrinics (except radial 2 lumbricals), sensory to hand
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(M1.AN.14.54) A 56-year-old woman is referred to a plastic surgeon for breast reconstruction approximately 18 months after undergoing right modified radical mastectomy for breast cancer. Physical exam demonstrates atrophy of the lower lateral pectoralis major muscle. Damage to which of the following nerves during mastectomy is the most likely cause of her atrophy? Tested Concept

QID: 106360
1

Long thoracic

31%

(30/96)

2

Intercostobrachial

4%

(4/96)

3

Medial pectoral

20%

(19/96)

4

Lateral pectoral

33%

(32/96)

5

Lateral intercostal

5%

(5/96)

M 1 D

Select Answer to see Preferred Response

(M1.AN.13.39) A 39-year-old male who recently presented with acetaminophen overdose was admitted to the MICU, where several attempts were made at obtaining intravenous access without success. The decision was made to place a right axillary arterial line, which became infected and was removed by the medical student while the patient was still intubated. It was later noticed that he had substantial swelling and bruising of the upper extremity. Given his sedation, a proper neuro exam was not performed at that time. Several days later, after the patient's liver function improved, he was successfully extubated. On exam, he complained of lack of sensation over the palmar and dorsal surface of the small finger and half of the ring finger, as well as weak digit abduction, weak thumb adduction, and weak thumb-index finger pinch of the affected extremity. What is the most likely cause and corresponding location of the injury? Tested Concept

QID: 106246
FIGURES:
1

Needle injury to ulnar nerve secondary to blind line placement

34%

(36/107)

2

Needle injury to median nerve secondary to blind line placement

7%

(8/107)

3

Compression of ulnar nerve secondary to coagulopathy

44%

(47/107)

4

Compression of median nerve secondary to coagulopathy

5%

(5/107)

5

Stretch injury to ulnar nerve secondary to frequent repositioning

5%

(5/107)

M 2 E

Select Answer to see Preferred Response

Evidence (2)
VIDEOS (1)
Topic COMMENTS (17)
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