Brachial Plexus Flashcards
What is the generic route of the brachial plexus?
- Runs from ventral rami of C5-T1 spinal roots emerging between anterior (attaches to rib 1) and medial scalene muscles (sits posterior of the anterior one) with the subclavian artery anterior
- Posterior neck triangle
- Mid point of clavicle and posteriorly
- Descends inferiorly and laterally to reach the upper limb running with and wrapping round the axillary artery
What is the point of having a plexus?
Nerves grow into the anterior and posterior condensations of mesoderm in the limb which means damage to a spinal nerve wont leave the entire limb paralysed
What muscle is just below the clavicle?
Subclavius
What occurs at the carotid artery bifurcation?
Baroreceptors present then artery splits into external and internal carotid arteries
What forms the posterior and anterior axillary folds?
Anterior: pectoralis major and minor
Posterior: latissimus dorsi and teres major
What is the axilla region? What does it contain?
Region superior to armpit connecting the neck to the upper limb bordered by pectoral girdle muscles and thoracic cage filled with fat with a tail of the breast extending into this region - it contains Neurovasculature of the upper limb (axillary artery and plexus sits in axillary sheath) and important lymph node groups
What can removal of lymph nodes lead to?
Lymphoedema
What areas do the axillary lymph nodes drain?
Anterior thoracic wall and breast
Posterior thoracic wall
Upper limb
Where can you palpate the subclavian artery?
Posterior to medial clavicle
What does the circumflex humoral run with and where is it?
Runs with axillary nerve + 5cm inferior to acromion
Describe the structure of brachial plexus from the neck to the upper limb.
- Roots (Rats): C5-T1 (C4 and T2 can sometimes be involved)
- Trunks (That): Upper (U), Medial (M) and Lower (L)
- Divisions (Do): anterior + posterior branch from each of the 3 trunks
- Cords (Cartwheels): lateral (2 x A from U and M), posterior (3 x P from U, M and L) and medial (A from L) in relation to axillary artery
- Branches (Badly):
- Lateralt -> musculocutaneous and median
- Posterior -> radial and axillary
- Medial -> median and ulnar
How can the musculocutaneous nerve be damaged? What is the consequence?
MoA: Direct damage is rare unless there is penetrating injury because its well protected by regional musculature
Consequence: Weakness/loss and paraesthesia/LOS of anterior arm compartment muscles so flexion of shoulder/elbow and supination of forearm (biceps brachii)
How can the axillary nerve be damaged? What is the consequence?
MoA: Dislocation of shoulder or # of surgical neck of humerus
Consequence: Weakness/loss and paraesthesia/LOS of deltoid muscles and teres minor
How can the median nerve be damaged? What is the consequence?
MoA: Stab or laceration to medial arm, anterior wrist or in tarsal tunnel
Consequence: Weakness/loss and paraesthesia/LOS of most anterior compartment forearm muscles, thenar muscles (base of thumb on palmar side of hand) and lumbricals 1 and 2 (go to 2nd and 3rd digit) i.e. intrinsic hand muscles
How can the radial nerve be damaged? What is the consequence?
MoA: # of humeral shaft through spiral groove, # of head/neck of radius, dislocation of head of radius from radio-ulna joint or compression at axillary region as posterior interosseous branch will be injured
Consequence: Weakness/loss and paraesthesia/LOS of posterior arm and posterior forearm compartment muscles
How can the ulna nerve be damaged? What is the consequence?
MoA: # of medial humeral epicondyle or injury to anterior wrist
Consequence: Weakness/loss and paraesthesia/LOS of most small intrinsic muscles of the hand
What are the 3 legs of the characteristic M seen of the brachial plexus in dissections?
Upper: Musculocutaneous
Medial: Median
Lower: Ulna
What nerve comes off of the posterior cord behind the axillary artery?
Axillary n.
What are the spinal root values of the nerves of the brachial plexus?
Musculocutaneous (C5-7) Axillary (C5-6) Median (C5-T1) Radial (C5-T1) Ulnar (C8-T1)
How can you damage the C5 root and upper brachial trunk?
Penetrating neck injury
If you could open an interval between the long and lateral tricep muscle heads, what would you see?
Radial nerve in the spiral groove on the back of the humerus
What are the smaller nerves of the brachial plexus formed by spinal nerves C5-6 primarily? What would happen if they was lost?
- Lateral pectoral: loss of clavicular head of pectoralis major
- Suprascapular: supraspinatus and infraspinatus (rotator cuffs) would be lost so shoulder lateral rotation and stability would be compromised
- Dorsal scapula: rhomboid function would be lost and levator scapulae would be affected too
How could the T1 root of the brachial plexus become compromised? What would be the consequence?
Sits superficial in thoracic cavity so is susceptible when there is lung apex pathology e.g. Pancoast tumour - most nerves end up in hand with ulna and radial n. so one of the first signs of a Pancoast tumour may be wasting of small hand muscles where the patient cannot perform dextrous movements with hands as well anymore
What is the nerve root of long thoracic nerve? What does it innervate and what would be the mechanism and consequence of damage?
Long thoracic n. (C5-7) supplies the serratus anterior and is vulnerable to damage stab injuries or interventions in the axillary region such as thoracostomy/thoracotomy if incision is too far posterior in the axillary region causing scapula ‘wings’
What does the medial pectoral nerve innervate?
Sternal head of pectoralis major and pectoralis minor
What does the upper subscapular nerve supply?
Subscapularis
What does the thoracodorsal nerve supply?
Latissimus dorsi
What does the lower subscapular nerve supply?
Subscapularis and teres major
What does the medial cutaneous nerves of the arm and forearm do?
Skin sensation
What is the large vein that sits near axillary artery that can be cannulated?
Axillary vein (will show dilations where valves are)
What muscle does the musculocutaneous nerve run through?
Coracobrachialis
Give the spinal root values of the muscles innervated by the radial nerve (C5-T1).
Brachioradialis (elbow flexor), radial wrist extenson and posterolateral dermatomes: C5-6
Triceps and digit extensors: C7-8
What are the borders of posterior triangle of the neck? What is palpable here?
- SCM
- Trapezius
- Clavicle
Upper part (C5-6) of brachial plexus
Why do limbs take on a different resting position when parts of the brachial plexus are damaged? Give an example.
Muscles innervated by the damaged part of the brachial plexus become weakened and waste whilst the remaining functional muscle groups pull the limb into a different resting position e.g. if the forearm supinators are lost via C5-6 loss, the pronator muscles will be unopposed leading to resting pronation of the forearm
What is Erb’s palsy?
C5-6 upper root/trunk damage of brachial plexus by forced separation of neck from shoulder via trauma (landing on shoulder), child-birth or stab wounds/lacerations that either stretch the roots or avulse them completely. This results in ‘waiters tip’ appearance of upper limb where the limb is medially rotated due to loss of lateral rotators, pronation due to loss of supinators and the limb hangs limp. The deltoid muscle will be wasted due to axillary nerve loss.
What is Klumpke’s palsy?
C8-T1 lower root damage/compression of the brachial plexus causing either stretch or complete avulsion as a result of upward traction of upper limb, cancer at lung apex (e.g. Pancoast tumour) or compression via a cervical rib. This will cause a claw hand deformity where the metacarpophalangeal joints (knuckles) are extended and interphalangeal joints are flexed constantly.
