15. SGT03 - The brachial plexus PDF

Preview

Summary

SGT03 - The brachial plexus...

Description

SGT 03: The brachial plexus and nerve distribution in the upper limb LO: Describe the boundaries and contents of the axilla, including the major vessels and relevant parts of the brachial plexus The Axilla  The axilla is the area that lies underneath the glenohumeral joint, at the junction of the upper limb and the thorax.  It is a passageway for neurovascular and muscular structures to enter and leave the upper limb. Borders of the Axilla  The overall 3D shape of the axilla is a pyramid.  It consists of four sides, an open apex and base: o Apex (axillary inlet) is formed by the:  lateral border of the first rib  superior border of scapula  the posterior border of the clavicle. o Lateral wall is formed by the  intertubercular groove of the humerus. o Medial wall consists of  the serratus anterior  the thoracic wall (ribs and intercostal muscles). o Anterior wall contains the  pectoralis major and underlying pectoralis minor  the subclavius muscles. o Posterior wall – formed by the  Subscapularis  teres major  latissimus dorsi.

Contents of the Axilla  Axillary artery (and branches): o The main artery supplying the upper limb. o It is commonly referred as having three parts:  one medial to the pectoralis minor  one posterior to pectoralis minor  one lateral to pectoralis minor o The medial and posterior parts travel in the axilla.  Axillary vein (and tributaries): the main vein draining the upper limb.  Brachial plexus (and branches) o NB: Axillary nerve leaves axilla via quadrangular space  Axillary lymph nodes:  Short head of Biceps brachii & coracobrachialis – these muscle tendons move through the axilla, where they attach to the coracoid process of the scapula.

LO: Describe the anatomy of the brachial plexus from its origin in the neck to its terminal branches. LO: Describe the origin, course and function of the axillary, radial, musculocutaneous, median and ulnar nerves in the upper limb LO: Name the major muscles and muscle groups that the axillary, radial, musculocutaneous, median and ulnar nerves supply, together with their sensory distribution. Brachial Plexus  The brachial plexus is a collection of spinal nerves that supply the skin and musculature of the upper limb.  It begins at the neck, passes through the axilla, and runs through the entire upper extremity.  The plexus is formed by the ventral rami of C5, C6, C7, C8 and T1.  The brachial plexus is divided into five parts; roots, trunks, divisions, cords and branches o Good mnemonic: Read That Damn Cadaver Book

Roots  The ‘roots’ refer to the anterior rami of spinal nerves C5, C6, C7, C8, and T1 that comprise the brachial plexus.

The spinal nerves pass between the anterior and medial scalene muscles to enter the base of the neck.

Trunks  At the base of the neck, the roots of the brachial plexus converge to form three trunks. o Superior trunk – a combination of C5 and C6 roots. o Middle trunk – continuation of C7. o Inferior trunk – combination of C8 and T1 roots. Divisions  Each trunk divides into two branches within the posterior triangle of the neck.  One division moves anteriorly (toward the front of the body)  The other division moves posteriorly (towards the back of the body).  Thus, they are known as the anterior and posterior divisions.  We now have three anterior and three posterior nerve fibres.  These divisions leave the posterior triangle and pass into the axilla. Cords  Once the anterior and posterior divisions have entered the axilla, they combine together to form three cords, named by their position relative to the axillary artery.  The lateral cord is formed by: o The anterior division of the superior trunk o The anterior division of the middle trunk  The posterior cord is formed by: o The posterior division of the superior trunk o The posterior division of the middle trunk o The posterior division of the inferior trunk  The medial cord is formed by: o The anterior division of the inferior trunk.  The cords give rise to the major branches of the brachial plexus. Major Branches  In the axilla and the proximal aspect of the upper limb, the three cords give rise to five major branches: The Musculocutaneous nerve, the Axillary nerve, the Median nerve, the Radian nerve and the Ulnar Nerve.  These nerves continue into the upper limb to provide innervation to the muscles and skin present. Musculocutaneous Nerve  Roots: C5, C6, C7. o Branch of the lateral cord  Anatomical Course: o Pierces coracobrachialis and passes down the anterior compartment of arm beneath biceps muscle. It continues into the forearm to become the lateral cutaneous nerve.  Motor Function: It innervates muscles in the anterior compartment of the arm  the brachialis, biceps brachii and coracobrachialis muscles  Sensory Functions: Gives off the lateral cutaneous nerve which innervates the skin of the lateral forearm

Region of sensory Innervation by Radial Nerve

Axillary Nerve  Roots: C5 and C6. o Direct continuation of the posterior cord  Anatomical Course: o passes beneath shoulder joint into the posterior compartment of arm and wraps around surgical neck of humerus  Motor Functions: Innervates the teres minor and deltoid muscles.  Sensory Functions: Gives off the superior lateral cutaneous nerve of arm, which innervates the inferior region of the deltoid (“regimental badge area”).

The sensory innervation of the axillary nerve. Known as the regimental badge area.

Median Nerve  Roots: C6 – T1. (+ C5 in some individuals). o Derived from medial and later cords  Anatomical Course o Runs down the arm with brachial artery, passes down through the cubital fossa into the anterior compartment of the forearm where it then divides into three terminal branches.  Motor Functions: o Innervates the flexor and pronator muscles in the anterior compartment of the forearm (except the flexor carpi ulnaris and part of the flexor digitorum profundus  innervated by the ulnar nerve) o Innervates the thenar muscles (associated with thumb) and the two lateral lumbricals muscles associated with the index and middle fingers.  Sensory Functions: o Palmar cutaneous branch innervates the lateral part of the palm, (does not pass through carpal tunnel) o Digital cutaneous branch which innervates the palmar surface and tips of the lateral three and a half digits.

Cutaneous innervation of the branches of the median nerve.

Radial Nerve  Roots: C5 – T1. o Continuation of the posterior cord  Anatomical Course: o Winds around radial groove of humerus and then passes into the posterior compartment of the forearm.  Motor Functions: o Innervates the muscle of the posterior compartment of the arm  the triceps brachii o Innervates the muscles in the posterior compartment of the forearm (which are primarily, extensors of the wrist and fingers).  Sensory Functions: There are four branches of the radial nerve that provide cutaneous innervation to the skin of the upper limb: o Lower lateral cutaneous nerve of arm – Innervates the lateral aspect of the arm. o Posterior cutaneous nerve of arm – Innervates the posterior surface of the arm.

Posterior cutaneous nerve of forearm – Innervates a strip of skin down the middle of the posterior forearm. o Superficial branch – innervates lateral 2/3 dorsum of the hand and the dorsal surface of the lateral three and half digits Sensory Summary: Innervates the posterior aspect of the arm and forearm, and the posterolateral aspect of the hand. o



Ulnar Nerve  Roots: C8 and T1. o Continuation of the medial cord  Anatomical Course o Runs down arm with brachial artery, passes behind medial epicondyle into forearm, then travels down anterior compartment of the forearm with ulnar artery to enter palm of the hand.  Motor Functions: o Innervates two of the muscles in the anterior compartment of the forearm (flexor carpi ulnaris and medial half of flexor digitorum profundus) o Innervates muscles in the hand (apart from the thenar muscles and two lateral lumbricals).  Sensory Functions: There are three branches of the ulnar nerve that are responsible for its sensory innervation. o Palmar cutaneous branch – innervates the medial 1/3 of the palm.

Dorsal cutaneous branch – innervates the dorsal surface of the medial one and a half fingers, and the associated dorsal hand area. o Superficial branch – innervates the palmar surface of the medial one and a half fingers. Sensory Summary: Innervates the anterior and posterior surfaces of the medial one and half fingers, and associated palm area. o



Cutaneous innervation of the ulnar nerve

M-Shape - Brachial Plexus 

The important structure to look for is an ‘M’ shape. This is formed by the musculocutaneous, median, and ulnar nerves, usually superficial to the axillary artery.

LO: Predict the consequences of injury to these nerves and describe how to test their functional integrity Upper brachial plexus Injury

  

Erb’s palsy refers to an injury to the upper roots of the brachial plexus (typically C5-6). It most commonly occurs as a result of a stretching injury during a difficult vaginal delivery. Consequences: o Loss of sensation over the lateral aspect of upper limb (C5-6 dermatomes) o Paralysis/weakening muscles supplies by nerves made up of roots C5-C6  Waiter’s Tip Position

Lower brachial plexus Injury  Klumpke’s palsy is an injury of the lower roots of the brachial plexus (C8-T1).  It is also most commonly associated with a difficult vaginal delivery  Consequences: o Loss of sensation along the medial side of upper limb (C8-T1 dermatome) o Paralysis/weakening of muscles supplies by nerves made up of roots C8-T1.  Clawed hand.

Injuries to Branches of the Brachial Plexus  An injury to one of the branches of brachial plexus will usually result in the weakening/paralysis of the muscles that are innervated by that specific nerves.

As a result, you may not be able to carry out the actions of which theses muscles play a major part. You will also get a loss of sensation to the region that was supplied by the nerve that has been injured o



Special Deformities  Median nerve injury: o Will result in the presentation of the Hand of Benediction on attempted finger flexion.  The patient cannot flex their index or middle fingers, resulting in unopposed extension of those two fingers.  Ulnar nerve injury: o Will result in the presentation of claw hand deformity on attempted finger extension  The patient cannot extend the IPJs of their ring or little fingers.  This results in fixed flexion of the IPJs and hyperextension of the MCPJs of these two fingers. o The clawed appearance is most pronounced when the nerve is injured at the wrist.  Radial nerve injury: o Will result in the presentation of wrist drop deformity at rest and on attempted wrist extension  The patient cannot extend their wrist/fingers, resulting in unopposed wrist flexion....