Brachial Plexus Anatomy & Injuries

• Academic year: 2024-2025
• Year: 1
• Semester: 2
• Module: Locomotor system (Ics) 105
• Topic: Anatomy of the brachial plexus and its injuries
• Presented by Dr. Eman Ramadan, Assistant Prof of Anatomy & Embryology, Zagazig University
• Department of Anatomy & Embryology

Objectives

• Define the brachial plexus.
• Identify the site and formation of the brachial plexus.
• Classify the brachial plexus as roots, trunks, divisions, and cords.
• Illustrate the branches of the cords.
• Differentiate between the common injuries of the brachial plexus.

Introduction

• The brachial plexus is the nerve plexus of the upper limb
• It provides motor and sensory supply to the upper limb
• The trapezius muscle, and the upper medial side of the arm are not supplied by the brachial plexus.

Brachial Plexus Site

• The brachial plexus originates in the posterior triangle of the neck, between the scalenus anterior and scalenus medius muscles
• It descends through the cervico-axillary canal to the axilla

Cervico-axillary Canal

• Connects the axilla to the root of the neck.
• Allows passage of nerves and vessels to and from the upper limb.
• Anteriorly: the middle third of the clavicle.
• Posteriorly: the superior border of the scapula.
• Medially: the outer border of the first rib.

Formation of Brachial Plexus

• Formed by the ventral rami of the lower four cervical nerves (C5, C6, C7, C8)
• Formed by the larger part of the ventral ramus of the 1st thoracic nerve (T1)

Ventral Rami Origin

• Ventral rami form from the nerve trunk of the spinal nerve.

Variations in Brachial Plexus Formation

• A prefixed plexus can occur when fibers from C4 join the brachial plexus
• A post-fixed plexus can occur when fibers from T2 join the brachial plexus

Stages of the Brachial Plexus

• Roots (ventral rami)
• Trunks
• Divisions
• Cords
• Branches

Location of Brachial Plexus Components

• Roots and trunks lie in the posterior triangle of the neck above the clavicle; this is the supraclavicular part
• Divisions lie in the cervico-axillary canal behind the clavicle; this is the retroclavicular part
• Cords and branches lie in the axilla below the clavicle; this is the infraclavicular part.

Roots

• Ventral rami of the lower four cervical nerves (C5, C6, C7, C8) and the larger part of the ventral ramus of the 1st thoracic nerve (T1).

Trunks and Divisions

• The ventral rami of C5 and C6 unite to form the upper trunk.
• The ventral ramus of C7 alone forms the middle trunk.
• The ventral rami of C8 and T1 unite to form the lower trunk.
• Each trunk divides into anterior and posterior divisions.

Cords

• There are three cords: medial, lateral, and posterior
• The anterior divisions of the upper and middle trunks unite to form the lateral cord
• The anterior division of the lower trunk alone forms the medial cord
• The posterior divisions of the three trunks unite to form the posterior cord

Branches from Roots

• Branches to the scalene muscles arise from C5,6,7,8
• Branches to the longus coli muscle arise from C5,6,7,8
• The root to the phrenic nerve arises from C5
• The dorsal scapular nerve (nerve to rhomboids) arises from C5
• The long thoracic nerve to the serratus anterior muscle arises from C5, 6, 7

Branches from Trunks

• The upper trunk is the only trunk that gives branches
• The nerve to the subclavius arises from C5,6
• The suprascapular nerve arises from C5,6

Branches from the Lateral Cord

• The lateral pectoral nerve arises from C5, 6, 7
• The lateral root of the median nerve arises from C5, 6, 7
• The musculo-cutaneous nerve arises from C5, 6, 7

Branches from the Medial Cord

• Medial pectoral nerve (C8, T1)
• Medial cutaneous nerve of the arm (C8, T1)
• Medial cutaneous nerve of the forearm (C8, T1)
• Medial root of median nerve (C8, T1)
• Ulnar nerve (C7, 8, T1)

Branches from the Posterior Cord

• Upper subscapular nerve (C5,6)
• Lower subscapular nerve (C5,6)
• Nerve to latissimus dorsi (C,6,7,8)
• Axillary nerve (C5,6)
• Radial nerve (C5,6,7,8 & T1)

Erb's Point

• It is the region of the upper trunk of the brachial plexus where six nerves meet
• The 5th and 6th cervical roots join to form the upper trunk
• The upper trunk gives off the suprascapular nerve and nerve to subclavius
• The upper trunk divides into anterior and posterior divisions

Interactive Questions

• Which nerve originates from the medial cord of the brachial plexus? The answer is the ulnar nerve
• An Injury of the lower trunk of the brachial plexus leads to which deformity? The answer is claw hand

Brachial Plexus Injuries

• Upper lesions of the brachial plexus involve Erb's Palsy and upper trunk injury
• Lower lesions of the brachial plexus involve Klumpke's paralysis and lower trunk injury

Causes of Upper Lesion of Brachial Plexus Injury

• In infants during a difficult delivery
• In adults after a blow to or fall on the shoulder
• Severe head traction during labor can damage the upper trunk

Muscles Affected in Upper Lesions (Erb's Palsy)

-C5 and C6 supply the following muscles -Supraspinatus and infraspinatus through the suprascapular nerve -Deltoid and teres minor through the axillary nerve -Biceps, brachialis, and coracobrachialis through the musculocutaneous nerve (C5, 6, 7).

Deformity in Upper Lesions

• Paralysis of the supraspinatus and deltoid leads to loss of abduction of the shoulder
• The arm hangs by the side.
• Paralysis of the flexors of the arm (brachialis, coracobrachialis, and biceps) leads to loss of flexion of the elbow, hence the elbow is extended
• Paralysis of the biceps leads to loss of supination of the forearm, hence it is pronated.
• The arm is adducted, pronated, medially rotated, and hanging by the side
• This is known as "Waiter's tip position".

Lower Lesions of the Brachial Plexus (Klumpke's Palsy)

• Occurs from a person falling from a height and grasping something to save their life
• Can also occur from a baby's upper limb being pulled excessively during delivery

Muscles Affected in Lower Lesions

• Fibers of C8 and T1 supply the small muscles of the hand.
• Action of lumbricals and interossei is mainly flexion of the metacarpophalangeal (MPJ) and extension of the interphalangeal joints (IPJ) of the medial four fingers (writing position).

Deformity in Lower Lesions

• The reverse occurs by the unopposed action of the extensor digitoreum.
• This leads to hyperextension of the metacarpophalangeal joints.
• The unopposed flexor digitorum superficialis and profundus lead to flexion of the interphalangeal joints of the medial four fingers
• Known as Complete Claw Hand

Comparison of Upper and Lower Lesions of Brachial Plexus

• Upper Type (Erb's Palsy):
  • Level of Lesion: C5,6 upper trunk
  • Cause: Difficult labor
  • Accidents on the same shoulder
  • Motor Loss: Proximal muscles
  • Sensory Loss: Lateral side of arm and forearm
  • Deformity: Waiter's tip position
  • Features: Arm hangs by the side, is medially rotated, and pronated
• Lower Type (Klumpke's Paralysis):
  • Level of Lesion: C8, T1 lower trunk
  • Cause: Person falls from a height then catches their fall, or from a difficult labor
  • Motor Loss: Distal muscles of the hand
  • Sensory Loss: Medial side of arm and forearm
  • Deformity: Complete claw hand
  • Features: Extension of MPJ and flexion of IPJ