Brachial Plexus

What are the axillary folds?

Anterior - pectoralis major and minor Posterior - latissimus dorsi and teres major Anterior and posterior axillary lines run vertically down from the anterior and posterior axillary folds

What are the borders of the posterior triangle?

Anterior - sternocleidomastoid Posterior - trapezius Inferior - clavicle In base of posterior triangle is the middle and anterior scalene muscles from which the brachial plexus emerges.

Describe the embryology of the brachial plexus

Anterior and posterior condensations of mesoderm tissue in the limb bud. Lines of nerves from the brachial plexus travel into the condensations. Brachial plexus made up of ventral rami of C5-T1 spinal nerves which mix together to form the upper, middle and lower trunks. These then form the posterior (going into posterior condensation) and medial and lateral (going into anterior condensation) *cords*. At the end of these cords are the named nerves. Posterior condensation forms the muscles of the posterior compartments (and for anterior).

What structures are drained by the axilliary lymph nodes?

Anterior thoracic wall and breast Posterior thoracic wall Upper limb Removal of nodes can lead to lymphoedema of the upper limb

What are the relations of the brachial plexus?

Brachial plexus emerges from between the scalene muscles in the neck. These can compress the plexus leading to thoracic outlet syndrome. First rib is related to lower part of plexus - can be affected by fractures. Plexus is wound around the subclavian/axillary artery (becomes axillary after first rib). Clavicle sits close. The lung apex presses against the T1 root of the brachial plexus.

What is the origin and route of the axillary artery?

Brachiocephalic trunk Common carotid and right subclavian Axillary artery (at 1st rib) Brachial artery (below teres major) Rich anastomoses between subclavian and axillary arteries

What is the root value and innervation of the radial nerve?

C5-T1 Triceps Bracioradialis (elbow flexor) Radial wrist extensor Posterolateral dermatomes Digit extensors Not all muscle supplied by all spinal nerves

What does the lateral pectoral nerve supply?

Clavicular head of pectoralis major. C5/6

What is Erb's palsy?

Damage to C5 & C6 upper root or trunk damage. *Pronation of forearm, flexion of wrist, medial rotation of shoulder*. Limp and loss of shoulder contour - wasting of deltoid. Loss of supraspinatous and infraspinatous - medial shoulder rotation Loss of biceps brachii - probated forearm Partial wristdrop / flexion at rest - loss of ECR Anaesthesia over C5-6 dermatomes. Can be caused by forced separation of neck from shoulder, or stab wound to neck, or pulling head away from shoulders during birth.

What is Klumpke's palsy?

Damage to C8 & T1 lower root damage/compression. Wasting of hand small muscles, guttering, claw hand deformity (extension of knuckle joint and flexion of interphalangeal joints at rest). Clawing of digits 2-5 at rest due to unopposed action of MCP extensors and IP long flexors. Anaesthesia on medial elbow, forearm and arm. Can be caused by cancer at lung apex, compression via cervical rib or upward traction injury (sharp upward movement of upper limb).

What structure surrounds the brachial plexus?

Fibrous sheath (*axilliary sheath*), keeps it together. Sheath links back up to fascia surrounding deep neck muscles. Infection can track from neck to upper limb.

What lymph node groups are found in the axilla?

Humeral, Subscapular and Pectoral all drain into the Central which drains into the Apical. This drains to the Supraclavicular nodes.

What is the consequence of damage to the musculocutaneous nerve?

Loss of anterior arm compartment muscles. Sensory loss on lateral aspect of forearm. Direct damage is rare - well protected by overlying muscle groups and bony structures.

What is the consequence of damage to the axillary nerve?

Loss of deltoid and teres minor (increased chane of shoulder dislocation). Can happen in fractures of surgical neck of humerus. Difficulty moving shoulder. Square shaped shoulder due to deltoid wasting. Sensory loss on lateral aspect of deltoid (skin).

What is the consequence of median nerve damage?

Loss of most anterior compartment forearm muscles, thenar muscles and lumbricals 1 & 2. Can be damaged by puncture injuries to medial aspect of arm or anterior aspect of wrist.

What is the consequence of ulnar nerve damage?

Loss of most small muscles of hand. Runs behind medial humeral epicondyle (palpable of medial aspect of elbow). Can also be injured as it runs anteriorly to wrist.

What is the consequence of damage to the radial nerve?

Loss of posterior arm and forearm compartment muscles. Vulnerable to damage where it runs past humeral shaft (spinal groove). Posterior interosseus nerve branch of radial nerve runs close to head of radius - fracture/dislocation here can damage this nerve. Paralysis of posterior compartment of forearm.

What effect can a lung tumour have on the brachial plexus?

Pancoast tumour - at apex of lung. Wasting of small muscles of hands due to T1 root damage (median and ulnar nerves).

What are the different parts of the plexus?

Randy Travis Drinks Cold Beer Roots Trunks - upper, middle and lower. Stacked on top of each other. Divisions - anterior and posterior. Posterior divisions join together to form the posterior cord. Cords - lateral, posterior and medial. Named according to relation to axillary artery. Branches - medial and lateral cords give off branches that join and form median nerve. Branches form an M shape. Lateral leg is musculocutaneous nerve, middle is median and medial is ulnar. Posterior cords divide into radial and axillary nerves.

What is the benefit of a plexus?

Spinal nerves share neurons meaning damage to one spinal nerve won't lead to limb paralysis.

Where is the axilla?

Superior to armpit. Connects neck to upper limb. Borders: Lateral - humerus Medial - thoracic wall Anterior - pectoralis major & minor Posterior - latissimus dorsi Brachial plexus, upper limb blood vessels run through it. Also contains lymph nodes that drain upper limb, thoracic cage and breast tissue.

What is does the dorsal scapula nerve supply?

Supplies rhomboid muscles any levator scapulae. Rhomboid muscles move scapula back toward midline - retraction of the scapula. Comes of C5 root of plexus. Runs down back. C5/6

What does the long thoracic nerve supply?

Supplies soratus anterior muscle. Moves scapula and keeps it in contact with wall of thorax. Damage leads to winging of scapula (axillary surgery). Runs down lateral aspect of thorax.

What does the suprascapular nerve supply?

Supplies supraspinator and infraspinator. Damage compromises shoulder lateral rotation and stability. Higher risk of shoulder dislocation. Comes of proximal part of trunk of brachial plexus. C5/6

What is the function of the thenar muscles?

Thumb movement and opposition. Required for fine dexterous tasks.

What is Wallerian degeneration?

When a nerve fibre is cut or crushed the part of the axon separated from the neurons cell body degenerates distal to the injury