Updated: 2/14/2018

Brachial Plexus

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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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Questions (5)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.AN.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? Review Topic

QID: 106360
1

Long thoracic

32%

(29/91)

2

Intercostobrachial

4%

(4/91)

3

Medial pectoral

20%

(18/91)

4

Lateral pectoral

34%

(31/91)

5

Lateral intercostal

4%

(4/91)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(M1.AN.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? Review Topic

QID: 106246
FIGURES:
1

Needle injury to ulnar nerve secondary to blind line placement

34%

(35/102)

2

Needle injury to median nerve secondary to blind line placement

8%

(8/102)

3

Compression of ulnar nerve secondary to coagulopathy

42%

(43/102)

4

Compression of median nerve secondary to coagulopathy

5%

(5/102)

5

Stretch injury to ulnar nerve secondary to frequent repositioning

5%

(5/102)

M1

Select Answer to see Preferred Response

PREFERRED RESPONSE 3
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