April 18, 2023 Theme III - Scientific Basis of Clinical Practice

A plexus is a network of intersecting (intermingle but don’t join) nerves. Ventral rami (not T2-T12) merge with one or more adjacent anterior rami to form major somatic plexuses in which fibers intermingle and form a new set of multisegmental peripheral nerves, which contain fibers from multiple spinal nerves. Most nerves in the upper limb arise from the brachial plexus, protected proximally by the cervico-axillary canal and the axillary sheath. It is a complex network of merging and separating nerves, 5Rm3Ts6Dm3Cs3B, formed by the union of ventral rami C5-T1, which constitute the roots of the plexus. Almost all branches (terminal outgrowths) arise in the axilla, after the plexus has crossed the first rib.

ROOTS (emerge from intervertebral foramina, pass between anterior and middle scalene with subclavian artery)

C5Dorsal scapular nerve

arises superiorly - rhomboids

C6 C7 C8 T1

Long thoracic nerve leaves posteriorly – serratus anterior

TRUNKS (inferior trunk passes through subclavian artery groove posterior to scalene tubercle on first rib)

Superior trunkSubclavian nerve inferiorly - subclaviusSuprascapular nerve (runs through foramen of superior transverse scapular ligament, then along spine and winds around lateral border for i/spinatous) – supraspinatous, infraspinatous

Middle trunk Inferior trunkWith subclavian artery, traverses groove posterior to scalene tubercle of first rib

DIVISIONS (divisions pass through cervicoaxillary canal, under coracoid process, merging to cords occurs infraclavicularly). Anterior divisions supply flexor compartments, posterior divisions supply extensor compartments.

Anterior Posterior Anterior Posterior Posterior Anterior

CORDS (surround the axillary artery posteriorly, medially, and laterally)

Lateral cord - LML Posterior cord - ULTRA Medial cord - MMMMU

BRANCHES

Terminal branches are MARMU: Musculocutaneous C5-C7 Axillary C5-C6 Radial all Median all Ulnar C7-T1

Lateral pectoral nerve passes costacoracoid membrane to reach deep surface of pectoral muscles

Musculocutaneous nerve pierces coracobrachialis, descends between biceps brachii and brachialis, continues as lateral cutaneous nerve of forearm

Lateral branch of median nerve merges with medial root lateral to axillary artery, passes slightly medially in cubital fossa

Radial nerve passes posterior to humerus in radial groove,

Upper subscapular nerve passes posteriorly to enter subscapular fossa

Thoracodorsal nerve runs inferolaterally to apical part of latissimus dorsi

Lower subscapular nerve

Axillary nerve

Medial branch of the median nerve merges with lateral root

Ulnar nerve

Medial pectoral, medial brachial/anterbrachial cuteneous

Pectoralis major, pectoralis minor

Biceps brachii, brachialis, coracobrachialis

Muscles of anterior compartment, some of palm

Post compartment of forearm, skin

Subscapularis Latissimus dorsi

Subscapularis, teres major

Deltoid, teres minor, shoulder joint

Muscles of anterior compartment, some of palm

Flexor carpi ulnaris, most palm muscles

BRACHIAL PLEXUS

April 18, 2023 Theme III - Scientific Basis of Clinical Practice

Recall that injection of anaesthesia into or around the axillary sheath (proximal artery, vein, nerve) combined with an occlusive tourniquet produces upper limb nerve block, in which sensation is blocked to all deep muscles of the upper limb and the skin distal to the elbow.

Brachial plexus injuries influence movements and cutaneous sensation in the upper limb, resulting in paralysis and anaesthesia. These may be the result of

April 18, 2023 Theme III - Scientific Basis of Clinical Practice

Recall that injection of anaesthesia into or around the axillary sheath (proximal artery, vein, nerve) combined with an occlusive tourniquet produces upper limb nerve block, in which sensation is blocked to all deep muscles of the upper limb and the skin distal to the elbow.

Brachial plexus injuries influence movements and cutaneous sensation in the upper limb, resulting in paralysis and anaesthesia. These may be the result of

A, C – Excessive increase in neck/shoulder angle cause

B – Waiter’s tip position

D, E – Upper limb pulled superiorly cause

F – Claw hand