Pectoral Region, Axilla, Brachial Plexus, and Upper Arm

Pectoral Region, Axilla, Brachial Plexus, Upper Arm

Introduction

glenoid labrum: fibrous CT lip which surrounds the cartilage of the glenoid fossa and provides increased stability

cubital fossa (antecubital fossa): hollow area on the anterior surface of the elbow

axilla: in the shape of a four sided pyramid; conduit for vessels and nerves from trunk to arm; also fat and lymph nodes

compartments of arm: divided by intermuscular septae

anterior: primarily flexion and pronation (palms towards posterior)

posterior: primarily extension and suponation (palms towards anterior)

Cutaneous Innervation

dermatomes: areas of skin which receive sensory innervation from a single spinal segment

C5, 6: lateral side of arm

C8-T1: medial side of arm

C6: thumb

C7: middle finger

C8: little finger

named nerve domains: areas of skin innervated by a single named nerve (may cross lines of dermatomes)

axillary: lateral side of deltoid

median: tip of index finger

radial: dorsal first web space

ulnar: tip of little finger

musculocutaneous: lateral aspect of arm

Surface Anatomy

anterior axillary fold: formed by lateral border of pectoralis major

acromion process

posterior axillary fold: formed by lateral border of latissimus dorsi and teres major

greater tubercle of humerus

Structures in Pectoral Region and Axilla

walls of the axilla

base: skin and fascia (armpit)

anterior: pectoralis major and minor; clavicle

posterior: scapula and subscapular m

medial: ribs, intercostal muscles, serratus anterior m

lateral: intertubercular groove of the humerus

pectoralis major

origin: sternal half of clavicle; sternum; cartilages of true ribs; aponeurosis of external obliques

insertion: lateral lip of bicipital groove of humerus

innervation: medial and lateral pectoral nerves

action: adducts arm; draws arm forward; rotates arm medially

pectoralis minor

origin: outer surface of upper margins of ribs 3-5

insertion: coracoid process

innervation: medial pectoral

action: lowers lateral angle of scapula; pulls shoulder forward

biceps brachii muscle

origin - short head: coracoid process

origin - long head: supraglenoid tuberosity

insertion: radial tubercle; to origins of forearm flexors via lacertus fibrosis

action: flexes and suponates forearm; flexes arm when forearm is fixed

innervation: musculocutaneous

subclavius muscle

origin: upper border of first rib and cartilage

insertion: groove under surface of clavicle

innervation: 5^th and 6^th cervical

coracobrachialis muscle

origin: tip of coracoid process

insertion: middle of medial border of humerus

innervation: musculocutaneous

action: flexion and adduction of arm

long throacic nerve: supplies serratus anterior

medial pectoral nerve: supplies pectoralis minor and pectoralis major

lateral pectoral nerve: supplies pectoralis major

Arteries and Veins

subclavian artery: branch of brachialcephalic trunk; runs under clavicle; changes name along course through arm

axillary artery: subclavian changes name after it passes first rib; three parts:

first part: first rib to superior border of pec minor; one branch

superior thoracic artery: supplies first 2-3 intercostal spaces

second part: runs behind pectoralis minor; two branches

thoracoacromial trunk: four branches (California Police Department - CaPD) – clavicular, axillary, pectoral, deltoid

lateral thoracic artery runs with long thoracic nerve; supplies serratus anterior

third part: inferior border of pec minor to inferior margin of teres major; three branches

anterior circumflex humoral: smaller branch; anastamosis with posterior circumflex

posterior circumflex humoral: larger branch; anastamosis with anterior circumflex

subscapular: decends inferiorly; bifurcates

thoracodorsal: supplies lattisums dorsi

circumflex scapular: runs to the posterior aspect of the scapula; teres minor, infraspinatus

brachial artery re-naming of axillary artery after the inferior margin of the teres major

axillary vein: continuous with basilic vein; inferior margin of teres major to first rib (subclavian v.)

basilic vein: originates from complex system in distal arm; runs along medial aspect of arm

cephalic vein:originates from complex system in distal arm; runs along lateral aspect of arm and in deltopectoral triangle

vena comitantes: generic name for veins which follow arteries; carry same name as the artery

axillary sheath: covers axillary artery, vein, and brachial plexus

quadrangular space: formed by teres major and minor, long and lateral heads of the triceps; posterior humeral circumflex artery and axillary nerve run through here

triangular space: formed by teres major and minor; circumflex scapular artery runs deep to space

triangular interval: formed by lateral and long heads of triceps; radial nerve and profunda brachii can be seen though here

Brachial Plexus

roots: ventral rami C5 - T1

long thoracic nerve: made up from branches of C5-C7

trunks: each trunk has into anterior and posterior branches which give rise to the cords

superior

suprascapular nerve: supraspinatus, infraspinatus

subclavian nerve subclavian muscle

middle

inferior

cords:

lateral

lateral pectoral nerve

medial

medial pectoral nerve

medial brachial cutaneous (sensory nerve)

medial antecubital cutaneous (sensory nerve)

posterior

upper subscapular nerve subscapularis

thoracodorsal nerve lattisimus dorsi

lower subscapular nerve subscapularis

terminal branches: (MUMRA)

anterior: musculocutaneous, ulnar, median

posterior: axillary, radial

plexus: network of nerves from different vertebral segments

there are 8 cervical spinal segments but only 7 cervical vertebrae due to the embryological fusion of the somites

the anterior-posterior divisions of the trunks gives rise to the anterior-posterior division of the arm

the brachial plexus runs between the scalene muscles and over the first rib Þ much potential for pinching

proximal-distal organization of innervation: proximal innervation comes from early spinal nerves; distal from late

musculocutaneous (C5-C7): muscles of brachium

median (C5-T1): muscles of antebrachium

ulnar (C8-T1): intrinsic muscles of hand

radial (C5-C8): muscles of posterior compartment; no muscles distal to the wrist!!!

Review of nerves (which ones give sensation where)

The UlnarÞ the tip of the pinkie

The medianÞ the tip of the index

The axillaryÞ the lateral aspect of the deltoid

The radialÞ dorsal 1^st web space

With fractures of the surgical neck of the humerus, motor function of the Radial nerve is tested by getting a thumb’s up, sensation by a pinprick in the webbing between the thumb and forefinger.

Upper brachial plexus injury (C5, C6) results in Erb’s Palsy ("waiter’s tip"), atrophy of the deltoid and internal rotation of arm, flexion of the wrist and loss of cutaneous sensation of the lateral aspect of the upper arm. This injury can be the result of stretching the neck of a baby during delivery or an accident that stops the shoulder from moving but not the head and trunk.

Lower Brachial plexus injury (C8, T1) results in a loss of fine motor control of the hand because of paralysis and anesthesia of the muscles and skin supplied by the ulnar nerve. This injury can result from pulling on a baby’s arm during a delivery.

Injury to the upper rami/roots results in proximal paralysis and anesthesia; Conversely injury to the lower rami/roots results in distal paralysis and anesthesia.

Bones of the Arm

Humerus – long bone of the upper arm, its head articulates with the scapula at the glenoid fossa. Close to the head are the greater and lesser tubercules, which are separated from each other by the bicipital groove (intertubercular sulcus). The diaphysis (shaft) of the humerus has on its posterior side a raised area where the Deltoid muscle inserts. This is known as the Deltoid tuberosity. At the distal end of the humerus the prominent medial epicondyle and lateral epicondyle flare to their respective sides. The ulnar nerve passes right behind the medial epicondyle. The trochlea is where the ulna articulates. The capitulum is on the lateral side and is where the head of the radius articulates. On the posterior side of the distal humerus the olecrannon fossa allows the olecrannon of the ulna to rest when the elbow is in extension.

Radius – the shorter of the two bones in the forearm has a proximal cylindrical head that articulates with the capitulum of the humerus, a smooth cylindrical neck, and an oval tuberosity distal to the neck where the biceps brachii inserts.

Ulna – the other forearm bone. The most proximal portion, the olecrannon can be felt as the bone of the elbow. The trochlear notch articulates with the trochlea of the humerus. The ulnar tuberosity is where the brachialis inserts.

Muscles of the Arm

biceps brachii, brachialis, coracobrachialis, triceps brachii, anconeus, brachioradialis, pronator teres, and Supinator

Pronator Teres

Origin: Humeral head from medial epicondylar ridge of the humerus and common flexor tendon. Ulnar head from the medial side of the coronoid process of ulna.

Insertion: Middle of the lateral surface of the radius

Function: pronates the forearm, assists in flexing the forearm

Nerve: Median

Artery: Anterior ulnar recurrent

Supinator

Origin: lateral epicondyle of humerus, lateral ligament of elbow, annular ligament of radius, supinator crest and fossa of the ulna

Insertion: lateral and anterior surface of radius in its upper 1/3^rd.

Function: supinates the forearm

Nerve: Deep branch of radial

Artery: radial recurrent, posterior interosseous of ulnar

Elbow – a collection of synovial joints (the Humero-Ulnar, Humero-Radial, and Proximal Radio-Ulnar joints) contained within a common joint capsule, functioning as a single hinge joint. The radius (on the thumbside of anatomical position) articulates with the ulna and capitulum and allows for pronation and supination. The joint capsule is weak but supported by medial and lateral collateral ligaments. The head of the radius is held in place by the annular ligament. (annulus~ring)

Supination, thumbs point laterally (like holding "soup"). Pronation, thumbs point medially ("pouring " out the soup)

Structures in the Arm

Collateral Circulation around the Elbow – the brachial artery is the main supply for the antebrachium and hand. In the cubital fossa it splits to form the ulnar and radial arteries. Collateral arteries from above the elbow anastomose with recurrent arteries from below the elbow to provide a rich blood supply for the elbow. This network can function as an additional source of blood for the forearm should the major arteries in the cubital fossa become compromised.

Cubital Fossa – the triangular, hollow area on the anterior surface of the elbow. Contains the Biceps Brachii tendon, the Brachial Artery and its bifurcation (Ulnar and Radial), the Brachial and the Median Cubital Veins, the Median and Radial Nerve.

Common site of venipuncture at Median Cubital Vein; stethoscope placement for taking bp

Boundaries: Proximal-line connecting Medial and Lateral Epicondyle

Lateral-medial surface of Brachioradialis
Medial-Lateral surface of Pronator Teres
Floor-Brachialis and Supinator
Roof-Skin, Superficial and Deep Fascia (including Bicipital Aponeurosis)

Biceps Brachii

Bicipital Aponeurosis – a triangular membranous band that runs from the biceps tendon across the cubital fossa and merges with the deep fascia over the flexor muscles in the medial side of the forearm. The proximal part can be felt where it passes obliquely over the brachial artery and median nerve. This protects the contents of the cubital fossa.

Brachialis muscle

Origin: lower 2/3^rds of the anterior surface of the humerus.

Insertion: Coronoid process and tuberosity of ulna

Function: flexes forearm

Nerve: Musculocutaneous, radial

Artery: radial recurrent, brachial

Musculocutaneous nerve – from the lateral cord; begins opposite the inferior border of the Pectoralis Minor, pierces the Coracobrachialis, and continues distally between the biceps and brachialis muscles, supplying those muscles. At the lateral border of the tendon of the biceps, it becomes the lateral antebrachial cutaneous nerve supplying skin of the forearm.

Lateral and Medial Antebrachial Cutaneous nerves- see above for lateral. Medial is one of the five branches off the medial cord of the brachial plexus. It supplies the skin over the medial arm and proximal forearm.

Median nerve – formed by both lateral and medial cords, the median nerve runs distally in the arm on the lateral side of the brachial artery until it reaches the middle of the arm where it crosses to the medial side and contacts the Brachialis muscle. The median nerve lies deep to the bicipital aponeurosis and median cubital vein when in the cubital fossa. The median nerve has no branches in the axilla or arm; it passes deep into the forearm, through the Pronator teres, to supply all but one and one half of the muscles in the forearm. It also supplies the articular branches to the elbow.

Brachioradialis muscle

Origin: proximal 2/3^rds of the lateral supracondylar ridge of the humerus, lateral intermuscular septum.

Insertion: lateral side of base of styloid process of radius

Function: flexes forearm after flexion has been started by biceps and brachialis; may also act as a semipronator and semisupinator

Nerve: radial

Artery: radial recurrent

Radial nerve – a direct continuation of the posterior cord; the largest branch of the brachial plexus, enters the arm posterior to the brachial artery, medial to the humerus and anterior to the long head of the triceps (the triangular interval). It passes inferolaterally with the profunda brachii artery around the body of the humerus in the radial groove. At the lateral border of the humerus the radial nerve pierces the lateral intermuscular septum and continues inferiorly between the brachialis and brachioradialis muscles to the level of the lateral epicondyle of the humerus where it divides into deep and superficial branches. Deep branch- supplies the Triceps, Brachioreadialis, and extensor muscles of the forearm. Superficial branch- supplies sensory fibers to the dorsum of the hand and digits.

Profunda Brachii artery – the most superior and largest branch of the brachial artery, accompanies the radial nerve in the radial groove. Posterior to the humerus it divides into anterior and posterior descending branches.

Spiral (Radial) groove – a shallow, oblique groove that extends inferolaterally on the posterior aspect of the humerus. The radial nerve travels in this groove between the lateral and medial heads of the triceps.

Coracobrachialis muscle – penetrated by the musculocutaneous nerve

Triceps Brachii muscle (Long, Lateral, and Medial heads)

Origin: Long head- from the infraglenoid tuberosity of scapula, Lateral head- from the posterior and lateral surfaces of humerus, medial head- from the lower posterior surface of humerus.

Insertion: Upper posterior surface of olecranon and deep fascia of forearm

Function: extends forearm; if arm is abducted, long heads aid in adducting it

Nerve: Radial

Artery: branch of profunda brachii

Anconeus muscle

Origin: lateral epicondyle of humerus, posterior ligament of elbow joint

Insertion: lateral side of olecranon and posterior surface of ulna

Function: assists triceps in extending forearm

Nerve: Radial

Artery: branch of profunda brachii

Brachial artery – the name for the artery that was the Axillary once the Axillary past distally to the Teres Major muscle.

Superior and Inferior Ulnar Collateral arteries- both arise from the brachial artery and anastomose with the posterior recurrent branch of the ulnar artery and themselves at the elbow.

Radial Recurrent artery – arises from the lateral side of the radial artery just distal to its origin, and ascends between the brachioradialis and the brachialis muscles. It supplies these muscles and the elbow joint and anastomoses with the radial collateral artery, a branch of the profundi brachii.

Radial artery – begins in the cubital fossa medial to the biceps tendon. This artery travels from the midpoint of the cubital fossa to the tip of the styloid process of the radius. The proximal portion of this artery is covered by the Brachioradialis muscle, the distal portion only by skin. Over the radius this artery is commonly used to measure the pulse rate.

Ulnar artery – like the Radial artery, this artery is also a terminal branch of the Brachial artery. The Ulnar artery begins just medial to the biceps tendon. With the median nerve the ulnar artery passes between the ulnar and radial heads of the flexor digitorum superficialis. About midway the between the elbow and wrist the ulnar artery crosses posterior to the median nerve to reach the medial side of the forearm.

Common Interosseous artery – a short branch of the ulnar artery, that arises in the distal part of the cubital fossa and divides in to the anterior and posterior interosseous arteries.