BRACHIAL PLEXUS Abraham A.A. Osinubi MBBS (Ibadan) M.Sc. Anatomy (Lagos) Ph.D. Anatomy (Lagos) FACE (USA)

Definition The brachial plexus is a somatic nerve plexus formed by intercommunications among the ventral rami of the lower four cervical nerves (C 5 - C 8) and the greater part of ventral ramus of first thoracic nerve (T 1)

Functions 1. The plexus is responsible for the motor innervation to all of the muscles of the upper limb with the exception of the trapezius & levator scapula

2. The brachial plexus supplies all of the cutaneous innervation of the upper limb with the exception of the area of the axilla (supplied by the intercostobrachial nerve) an area just above the point of the shoulder (supplied by supraclavicular nerves) the dorsal scapular area which is supplied by cutaneous branches of dorsal rami

The brachial plexus communicates with the sympathetic trunk by communicantes that join all the roots of the plexus and are derived from the middle & inferior cervical sympathetic ganglia & the first thoracic sympathetic ganglion

Variations Prefixed Brachial Plexus Postfixed Brachial Plexus Occurs when the C 4 ventral ramus contributes to the brachial plexus Contributions to the plexus usually come from C 4 - C 8 + T1 is reduced Postfixed Brachial Plexus Occurs when the T 2 ventral ramus contributes to the brachial plexus Contributions to the plexus usually come from C 6 - T 2 + contribution of C5 is reduced

Formation

Roots The ventral rami of spinal nerves C5 to T1 are referred to as the roots of the plexus Lie behind scalenus anterior muscle

Trunks Shortly after emerging from the intervertebral foramina , the 5 roots unite to form 3 trunks The ventral rami of C5 & C6 unite to form the Upper Trunk The ventral ramus of C7 continues as the Middle Trunk The ventral rami of C8 & T 1 unite to form the Lower Trunk Emerge from lateral border of scalenus anterior & cross post triangle

Divisions Each trunk splits into an anterior & a posterior division The anterior divisions usually supply flexor muscles The posterior divisions usually supply extensor muscles Behind the clavicle

Cords The anterior divisions of the upper & middle trunks unite to form lateral cord The anterior division of lower trunk forms the medial cord All 3 posterior divisions from each of 3 cords all unite to form posterior cord The cords are named according to their position relative to the axillary artery At the outer border of first rib

Terminal Branches (I) (n=5). Mixed nerves containing sensory & motor axons Musculocutaneous n. Derived from lateral cord (C5,6,7) Innervates muscles in flexor compartment of arm Carries sensation from lat (radial) side of forearm

Terminal Branches (II) Median n. Derived from lateral & medial cords Lat root= C6,7; Med root= C8,T1 Motor innervation-most of flexor muscles in forearm & intrinsic muscles of thumb (thenar m.) Sensory innervation from lateral (radial) 3½ digits Ulnar n. Derived from the medial cord C7,C8,T1 Motor innervation mainly intrinsic muscles of hand Sensory innervation- medial (ulnar) 1½ digits

Terminal Branches (III) Axillary n. Derived from the posterior cord C5,6 Motor innervation- deltoid & teres minor Sensory innervation- skin just below the point of the shoulder Radial n. Derived from the posterior cord C5-C8,T1 Called “Great Extensor Nerve”: innervates extensors of elbow, wrist & fingers Sensory innervation- dorsum of the hand on the radial side

BRANCHES

Nerves to scaleni & longus colli (C5-8) Branch to phrenic n (C5) From the Roots Dorsal Scapular nerve Derived from C5 Motor nerve to the Rhomboideus major & minor muscles Long Thoracic nerve Derived from C5,6,7 Innervates the serratus anterior muscle Nerves to scaleni & longus colli (C5-8) Branch to phrenic n (C5)

From the Upper Trunk Nerve to subclavius muscle (C5,6) Suprascapular nerve (C5,6) Innervates supra & infraspinatus muscles

From the Lateral Cord Lateral pectoral nerve (C5,6,7) innervates pectoralis major (clavicular or upper head) & pectoralis minor Lateral root of the median nerve (C6,7)

Medial pectoral nerve (C8,T1) innervates pectoralis major & minor From the Medial Cord Medial pectoral nerve (C8,T1) innervates pectoralis major & minor Medial cutaneous nerve of the arm (medial brachial cutaneous) (C8,T1) innervates the medial portion of the arm Medial cutaneous nerve of the forearm (medial antebrachial cutaneous) (C8,T1) innervates the medial half of the forearm Medial root of the median nerve (C8,T1) contributes to the median nerve

Note The medial & lateral pectoral nerves often join together to act as a single nerve innervating both the pectoralis major & minor muscles

Applied & Clinical Anatomy

Shoulder ABD & LAT/ROT – C5 ADD & MED/ROT – C6,7,8 FLEX & EXT- C6,7,8 Elbow FLEX- C5,6 EXT- C7,8 Supination (Med n) & Pronation (M-C n) C6,7 Wrist FLEX- C6,7 EXT- C6,7 Fingers Hand (Intrinsic muscles)- T1

NERVE Long Thoracic (C5,6,7) MOTOR DEFICITS Winged Scapula- Serratus Anterior SENSORY None Suprascapular (C5,6 ) Difficult to initiate shoulder abduction – Supraspinatus Axillary (C5,6) Difficult abducting arm to horizontal – Deltoid Lateral side of arm; below point of shoulder Loss of shoulder roundness – Deltoid Musculocutan. (C5,6,[7]) Very weak flexion of elbow joint- Biceps & Brachialis Lateral forearm Weak supination of sup radioulnar joint –Biceps

NERVE Radial (C5 - T1) MOTOR DEFICITS Drop Wrist – Extensor carpi radialis longus & brevis, Ext. carpi ulnaris SENSORY DEFICITS Posterior aspect of arm & forearm; Radial 2/3 of dorsum of hand & proximal parts of dorsal surfaces of lateral 3½ fingers Difficulty making a fist - synergy between wrist extensors and finger flexors

Median (C5 - T1) at Elbow Pronation of radioulnar joints-Pronator teres & quadratus Radial portion of palm; palmar surface & tips of radial 3½ digits Weak wrist flexion - Fl. Carpi radialis Weakened opposition of thumb - thenar muscles “Ape Hand”- thumb hyper extended and adducted - thenar muscles “Papal Hand” Loss of flexion of I.P. joints of thumb & fingers 2 & 3 - Fl. pollicis longus; Fl. digit. superficialis, Fl. digit profundus (C5 – T1) at Wrist Palmar surface & tips of radial 3½ digits

Ulnar (C8, T1) at Elbow “Clawing” of fingers 4 & 5- M.P. joints hyper extended; P.I.P. Flexed - Interossei & Lumbricals Ulnar and dorsal aspect of palm and of ulnar 1½ digits Loss of abduction & adduction of M.P joints of fingers –Interossei Thumb - abducted and extended - adductor pollicis Loss of flexion of D.I.P. joints of fingers 4 & 5 - Fl. digit profund. at Wrist Loss of abduction & adduction of M.P joints of fingers – Interossei Thumb - abducted & extended - adductor pollicis

UPPER AND LOWER ROOT LESIONS

Lesion Motor Deficits Sensory Deficits Nerves Erb’s Palsy (C5,6) Loss of abduction, flexion & rotation at shoulder; Weak shoulder extension – deltoid, rotator cuff Posterior & lateral aspect of arm - axillary n. Axillary, Suprascapular, Upper & Lower subscapular Very weak elbow flexion and supination of radioulnar joint – biceps brachii & brachialis Radial side of Forearm- m/c n. Thumb & 1st finger –Superf br. of radial; digital brs–Median n. Musculocutaneous; Radial n. brs. to supinator & brachioradialis muscles Susceptible to shoulder dislocation - loss of rotator cuff muscles “Waiter’s Tip”position- arm add, elbow ext, wrist flex

Loss of opposition of thumb -Thenar muscles Sensory Deficits Lesion Klumke’s Palsy (C8,T1) Motor Deficits Loss of opposition of thumb -Thenar muscles Sensory Deficits Ulnar side of Forearm & Hand & ulnar 1½ digits Nerves Thenar branch of Median Loss of adduction of thumb - Adductor pollicis Ulnar nerve Loss of abduction and adduction of M.P. joints; flexion at M.P. & extension of I.P. joints. Lumbricals & interossei Ulnar & Median Very weak flexion of P.I.P. & D.I.P. joints. Fl. Digit. Super. & Profund.

There are 4 types of nerve injuries: Avulsion: the nerve is torn from the spine. Rupture: the nerve is torn but not where it attaches to the spine. Neuroma: the nerve has tried to heal itself, but scar tissue has grown around the injury. The scar tissue puts pressure on the injured nerve. As a result, the nerve cannot conduct signals to the muscles. Praxis: the nerve has been damaged but not torn. These injuries heal on their own. If your patient has praxis, you should see improvement within 3 months.

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