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Brachial Plexus Advanced lecture - Usmle Fast Track mode ( not for beginners ) Dr Bhanu prakash
Brachial Plexus Advanced Lecture
The brachial plexus and the subclavian artery traverse the posterior triangle of the neck and the interscalene triangle
Interscalene triangle: formed by the 1st rib, scalenus anterior, and scalenus medius.
Scalenus anticus syndrome: neurologic and/or vascular impairment of the upper limb due to narrowing of the interscalene triangle and consequent compression of the brachial plexus and subclavian artery
The brachial plexus and the subclavian vessels are protected from the sharp ends of a fractured clavicle by the subclavius
The clavicle is the most frequently fractured bone in the body.
Subclavius: a muscle innervated by the ‘nerve to the subclavius’ which branches from the superior trunk of the brachial plexus.
Use the mnemonic “Real Texans Drink Cold Beer” to remember the proximal-to-distal organization of the brachial plexus: Roots → Trunks → Divisions → Cords → Branches
5 Roots: ventral rami of C5, C6, C7, C8, T1
3 Trunks:
- Superior (upper) trunk (C5, C6)
- Middle trunk (C7)
- Inferior (lower) trunk (C8,T1)
6 Divisions: an anterior and posterior division for each of the 3 trunks
3 Cords (named according to their anatomic relationship to the axillary artery):
- posterior cord → axillary nerve, radial nerve
- lateral cord → musculocutaneous nerve, part of median nerve
- medial cord → ulnar nerve, part of median nerve
5 terminal Branches: axillary, radial, musculocutaneous, median, ulnar nerves
Erb’s palsy (Waiter’s tip): lesion of the upper trunk (C5-C6) of the brachial plexus.
Injury to roots C5 and C6 affects the deltoid, rotator cuff, elbow flexors, wrist and hand extensors
Latissimus dorsi is innervated by the middle subscapular (thoracodorsal) nerve, which is mostly derived from C7 ∴ not affected in Erb’s palsy
Because the deltoid and rotator cuff muscles are paralyzed due to injury of C5 and C6, the action of latissimus dorsi on the shoulder (extension, adduction, medial rotation) is unopposed ∴ the arm hangs by the side (adduction) and is internally (medially) rotated
Klumpke’s palsy: lesion of the lower trunk (C8-T1) of the brachial plexus.
Affects the wrist flexors and the intrinsic muscles of the hand (thenar/hypothenar muscles, volar and dorsal interossei, and lumbricals)
Injury of C8-T1 may also involve the sympathetic trunk/ganglia → Horner’s syndrome:
(1) Miosis
(2) Anhidrosis
(3) Ptosis
Winged Scapula: lesion of the long thoracic nerve
Serratus anterior is innervated by the long thoracic nerve, formed by ventral rami of spinal nerves C5, C6, C7
Actions of serratus anterior:
- upward rotation of the scapula: serratus anterior is responsible for shoulder abduction above the horizontal plane - “C5, 6, 7 points to heaven”
- protraction and depression of the scapula
Lesion of the long thoracic nerve (eg, status post mastectomy with axillary lymph node dissection) → paralysis of serratus anterior →
(1) inability to raise the arms above the horizontal (90°)
(2) medial winging of the scapula (inferior scapular angle is rotated medially and lifted superiorly and away from the posterior thoracic wall), which may be accentuated by having the patient push against a wall with flat palms
Compare:
Lesion of accessory nerve (CN 11) (eg, radical neck dissection) → paralysis of trapezius →
(1) drooping of the shoulder
(2) lateral scapular winging (inferior scapular angle is rotated laterally and lifted superiorly and away from the posterior thoracic wall), which may be accentuated during resisted abduction. usmle videos pathology usmle step 1 pharmacology
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