ClavicleDr Henry Knipe◉ and Dr Ayush Goel et al.

The clavicle (or informally collar bone) is the only long bone that lies horizontally in human skeleton. 

Gross anatomyOsteology

The clavicle is roughly "S-shaped" with a flattened, concave, lateral one-third and a thickened, convex, medial two-thirds. One the inferior surface of lateral third is the conoid tubercle for the attachment of the conoid ligament and lateral to this is the trapzeoid line for attachment of the trapezoid ligament. On the inferior surface of the medial clavicle is the costal tuberosity and groove for subclavius for the attachment of sternocostal ligament and subclavius muscle respectively. 

The female clavicle is shorter, thinner and less curved than the male clavicle. 

Articulations

The clavicle articulates with acromion at the acromioclavicular joint laterally and thesternum at the sternoclavicular joint medially.

Attachments

muscles: pectoralis major, sternocleidomastoid (clavicular head), deltoid,trapezius, subclavius

ligamentous: acromioclavicular ligament, coracoclavicular ligament, sternoclavicular ligaments

DevelopmentOssification

It is the first bone to start ossification at around 5th-6th weeks of gestation but finishes around 21-25 years of age. The lateral end has intramembranous ossification. See main article: ossification centres of the pectoral girdle. 

Variant anatomy forked clavicle

supraclavicular foramen : the clavicle may be pierced by a branch of supraclavicular nerve

coracoclavicular joint

Radiographic appearancePlain films

On a chest x-ray image, the clavicles are superimposed over the apex of both the lungs and obscure the subtle lesions. An apical or lordotic view may then provide greater detail of the lung apices.

Chest x-rays are correctly aligned if the medial ends of clavicles are equidistant from spinous process of vertebrae at the T4/5 level. 

The conoid tubercle (also known as the coracoid tuberosity) is a bony prominence on the inferior surface of the lateral third of the clavicle. 

It marks the insertion of the conoid ligament (which along with the trapezoid ligament) forms part of the coracoclavicular ligament complex.

Coracoclavicular jointDr Dalia Ibrahim and Dr Frank Gaillard◉ et al.

The coracoclavicular joint is a normal variant of the pectoral girdle, where the conoid tubercle of the clavicle appears enlarged or elongated, with a flattened inferior surface where it approximates the coracoid process of the scapula to form an articulation. 

EpidemiologyMore common in Asians than in Africans or Europeans with a prevalence of ~10% (range 0.5-20%) with equal male:female distribution 1-2,4. 

Gross anatomyThe coracoclavicular joint represents a true synovial articulation between the conoid tubercle of the clavicle and the superior surface of coracoid process of the scapula. This accessory articulation may be found either unilaterally or bilaterally. 

Sternoclavicular jointDr Henry Knipe◉ et al.

The sternoclavicular joint is a diarthrodial synovial articulation between the medialclavicle, manubrium and the first costal cartilage that joins the upper limb with the axial skeleton. 

Gross anatomyThere are two non-congruent articular surfaces forming a saddle-type joint 3:

medial clavicle: larger of the two

clavicular notch of the sternum: smaller of the two

The articular surfaces are covered with fibrocartilage (rather than hyaline cartilage is in most other synovial joints). The joint space is divided into two separate recesses by a fibrocartilage articular disc 1, 2. 

Ligaments

Because of the non-congruent articular facets much the joint stability comes from surrounding ligaments 3, 4: 

anterior and posterior sternoclavicular ligament; thickenings of the joint capsule

interclavicular ligament: between superomedial ends of the clavicles

costoclavicular ligament

Special structures

articular disc 

o flat and oval in shape

o made of fibrocartilage (like the mensici of the knee and labrum of the hipand shoulder)

o attached to the joint capsule anteriorly and posteriorly, first costal cartilage inferiorly and the

clavicle superiorly

Relations

anteriorly: sternocleidomastoid muscle 3

posteriorly: sternohyoid muscle, sternothyroid muscle, brachiocephalic veins, origin of the great vessels 2

Blood supply arterial: internal thoracic and suprascapular arteries 5

Nerve supply medial supraclavicular and subclavian nerves 5

Variant anatomy ~2.5% of the population have an inferior facet for articulation with the first rib 3

perforation of the articular disc, meaning the joint recesses are in communication 3

Related pathology sternoclavicular joint dislocation

site of septic arthritis, especially in intravenous drug users 4

SAPHO syndrome

ScapulaDr Yuranga Weerakkody◉ and Dr Tim Luijkx et al.

The scapula (plural: scapulae) is a roughly triangular shaped bone of the pectoral girdle with several articulations connecting to the humerus and clavicle. 

Gross anatomyOsteology

The main part of the scapula, the body, consists of a somewhat triangular-shaped flat blade, with an inferiorly pointing apex, referred to as the inferior angle as well as lateral and superior angles. The scapula is described as having superior, medial, and lateral borders. 

Posteriorly, the scapula is divided into a supraspinous fossa and infraspinous fossa by the scapular spine. Anteriorly, on the costal surface, is the shallow subscapular fossa. 

Laterally is the glenoid fossa, anteriorly is the coracoid process and superiorly is the acromion that is continuous with the scapular spine and arcs anteriorly over the humeral head. The suprascapular notch lies immediately medial to the base of the coracoid process. The spinoglenoid notch lies posteriorly behind the neck.

Articulations

coracoid process: clavicle (forming the acromioclavicular joint)

glenoid cavity: humeral head (forming the glenohumeral joint)

Attachments

Musculotendinous

supraspinous fossa: supraspinatus muscle

infraspinous fossa: infraspinatus muscle, teres minor muscle

subscapular fossa: subscapularis muscle, serratus anterior

acromion: acromial part of deltoid muscle, trapezius

scapular spine: spinous part of deltoid muscle, trapezius

lateral border (margo lateralis): teres minor muscle, teres major muscle

vertebral border (posterior): levator scapulae, rhomboid minor muscle, rhomboid major muscle

inferior angle: teres major muscle, latissimus dorsi (small slip)

supraglenoid tubercle: long head of biceps muscle

infraglenoid tubercle: long head of triceps muscle

Ligamentous

transverse scapular ligament: crosses suprascapular notch, with the suprascapular nerve below (within the resulting foramen) and the suprascapular vessels above

coracoacromial ligament

coracoclavicular ligament

coracohumeral ligament

glenohumeral ligaments: upper, middle, and lower bands

acromioclavicular ligament (weak)

Blood supplyThe scapula is a site of arterial anastomosis between many arteries. This aims to ensure an adequate supply of blood to the upper limb, but has added benefit of adequate supply to the bone itself.

suprascapular artery

dorsal scapular artery

branches of subscapular artery (i.e. circumflex scapular artery)

Variant anatomy Sprengel deformity

DevelopmentSee "ossification centres of the pectoral girdle" for information on the scapular ossification centres.

Anterior compartment of the armDr Henry Knipe◉ and Dr Elena Trajcevska et al.

The anterior compartment of the arm is one of the two compartments of the arm.

A sheath of deep fascia surrounds the arm, the brachial fascia. Two intermuscular septae (medial and lateral) extend from it to attach to the humerus at the medal condylar ridge and lateral supracondylar ridge, respectively. These septae divide the arm into its anterior and posterior compartments.

MusclesThree flexors:

biceps brachii

brachialis

coracobrachialis

Biceps brachiiDr Henry Knipe◉ and Dr Jeremy Jones◉ et al.

The biceps brachii muscle (also known simply as biceps) is a two-headed muscle in the anterior compartment of the arm that flexes at the elbow and supinates the forearm.

origin

o short head: coracoid process (of the humerus)

o long head: supraglenoid tubercle of the scapula

insertion: radial tuberosity of the proximal radius

innervation: musculocutaneous nerve

action

o shoulder joint

long head: arm abduction

short head: arm adduction and ventral flexion

o elbow joint

supination of the pronated forearm

flexion of the supinated forearm

BrachialisDr Henry Knipe◉ and Dr Jeremy Jones◉ et al.

The brachialis muscle (brachialis) is one of the three muscles of the anterior compartment of the arm.  It is only involved in flexion at the elbow and therefore the strongest flexor at the elbow, c.f. biceps brachii which is also involved in supination because of its insertion on the radius.

origin: lower portion of the medial surface of the humerus

insertion: ulna tuberosity and coronoid process of the ulna

innervation: musculocutaneous nerve and radial nerve (proprioceptive branch)

action: flexion at the elbow

CoracobrachialisDr Jeremy Jones◉ et al.

The coracobrachialis muscle (or more simply coracobrachialis) is one of the three muscles of the anterior compartment of the arm that acts to perform flexion at the elbow. It sit beneath biceps brachii.

origin: coracoid process of scapula

insertion: via a flat tendon onto the midportion of the medial surface ofhumerus

innervation: musculocutaneous nerve (C6 and C7)

action: ventral shoulder flexion and shoulder adduction

Blood supply brachial artery

Brachial arteryDr Henry Knipe◉ et al.

The brachial artery is the main supply of arterial blood to the arm, forearm and hand. 

Summary origin: continuation of the axillary artery distal to teres major

location: medial upper arm

supply: muscles of the arm, forearm and hand

main branches: profunda brachii

terminal branches: radial and ulnar arteries

Nerve supplyPrimarily by the musculocutaneous nerve (C5,6), although the radial nerve (C7) does supply a small lateral part of brachialis.

Radial nerveDr Yuranga Weerakkody◉ and Dr Henry Knipe◉ et al.

The radial nerve is one of five main branches of the brachial plexus. It provides motor and sensory innervation to the arm and forearm and sensory innervation to the hand. 

Summary origin: one of the two posterior cords of the brachial plexus

course: posteromedially with the axillary vessels, behind the humerus, then anteriorly towards the elbow where it divides into superficial and deep branches

terminal branches: posterior interosseous (deep) and superficial radial nerves

motor: wrist and finger extension

sensory: dorsal aspect of the thumb, index and middle fingers

Gross anatomyOrigin

The radial nerve is one of two terminal branches of the posterior cord of the brachial plexus. It receives contributions from C8-T1 nerve roots.

Course

The radial nerve lies posterior to the axillary artery in the axilla and enters the posterior compartment of the arm under teres major muscle. 

In the posterior compartment of the arm, it winds it way around the spiral groove of the humerus, accompanying profunda brachii artery. It pierces the lateral intermuscular septum to enter the anterior compartment of the arm, then passes to the forearm by coursing anterior to the lateral epicondyle at

the level of the elbow joint. It enters the cubital fossa, where it divides into superficial and deep branches. 

The superficial branch courses towards the wrist lateral to the radial artery and enters the hand, dividing into the dorsal digital cutaneous branches. 

The deep branch gives off the posterior interosseous nerve, which passes between the heads of the supinator muscle to enter the posterior compartment of the forearm and it terminates at the level of the wrist joint. 

Branches and supply

muscular twigs in the arm - triceps brachii and anconeus muscles

superficial branch of the radial nerve - supplies cutaneous sensation to the dorsal aspect of the hand and dorsal aspect of the first to third digits and the dorsal lateral aspect of the fourth finger

deep branch of the radial nerve

o posterior interosseous nerve - extensor muscles in the forearm as well as brachioradialis

articular twigs to the elbow and wrist joints

Related pathologyRadial nerve pathology is complex and can occur at any level (axillary, spiral groove, radial tunnel, posterior interosseous, superficial radial):

radial tunnel syndrome

radial nerve palsy

radial nerve entrapment

Posterior compartment of the armDr Elena Trajcevska et al.

The posterior compartment of the arm is one of the two compartments in the arm.

The arm is separated into its anterior and posterior compartments by two intermuscular septae (medial and lateral).

MusclesOne extensor:

triceps brachii

anconeus

articularis cubiti

Triceps brachiiDr Henry Knipe◉ et al.

Triceps brachii (also known as simply the triceps) is a three-headed muscle in the posterior compartment of the arm.

origin:

o long head: infraglenoid tubercle of the scapula

o medial head: posterior humerus, superior to the radial groove

o lateral head: posterior humerus, inferior to the radial groove

insertion: olecranon of the ulna

innervation: radial nerve

actions:

o extensor of the elbow joint

o assists in extension of the shoulder joint (long head only)

AnconeusDr Matt A. Morgan◉ and Dr Henry Knipe◉ et al.

The anconeus is a small muscle in the posterior compartment of the arm. It has little functional significance but should be differentiated from the variably present anconeus epitrochlearis. 

Articularis cubitiDr Henry Knipe◉ et al.

The articularis cubiti is a muscle in the posterior compartment of the arm:

origin: posterior surface of the distal humerus

insertion: posterior surface of the elbow   joint capsule

innervation: radial nerve

action: tenses the posterior elbow joint capsule during elbow extension

Summary origin: lateral epicondyle of the humerus

insertion: olecranon of the humerus

innervation: radial nerve

action: elbow extension (weak)

Blood supply profunda brachii artery

ulnar collateral arteries

Nerve supply

radial nerve  (C7, 8)

Anterior compartment of the forearmDr Jeremy Jones◉ and Dr Henry Knipe◉ et al.

The forearm is divided in the anterior compartment and the posterior compartmentby the deep fascia, lateral intermuscular septum and the interossseous membrane between the ulna and radius. 

MusclesThe eight muscles located in the anterior compartment of the forearm can be divided into three layers - superficial, intermediate and deep. 1

Superficial layer

pronator teres

flexor carpi radialis  (FCR)

flexor carpi ulnaris  (FCU)

palmaris longus

Deep layer

flexor digitorum profundus

flexor pollicis longus

pronator quadratus

Pronator teresDr Henry Knipe◉ et al.

Pronator teres is a two-headed flexor and pronator of the forearm found in its anterior compartment. 

origin

o humeral head - medial epicondyle of the humerus

o ulnar head - coronoid process of the ulna

insertion - lateral surface of the middle-third radius

innervation - median nerve

action - weak flexor at the elbow joint; strong pronator of the forearm joints

Flexor carpi radialis

Dr Tim Luijkx and Dr Henry Knipe◉ et al.

Flexor carpi radilalis (FCR) is a muscle found in the first layer of the anterior compartment of the forearm.

Summary origin: medial epicondyle of the humerus

insertion: base of the 2nd and 3rd metacarpals

innervation: median nerve (C6-7)

action: It is flexor and adductor of the wrist joint

Intermediate layer

flexor digitorum superficialis  (FDS)

Deep layer

flexor digitorum profundus  (FDP)

flexor pollicis longus  (FPL)

pronator quadratus

Blood supply arterial supply - ulna artery, radial artery

Nerve supplyThe median nerve supplies the anterior compartment musculature except the ulna (medial) part of FDP and FCU, which are supplied by the ulna nerve. 

Median nerveDr Yuranga Weerakkody◉ and Dr Mohammad Taghi Niknejad et al.

The median nerve is one of the five main nerves originating from the brachial plexus and provides motor and sensory innervation to parts of the forearm and hand. 

Summary origin:

o lateral root - lateral cord of the brachial plexus

o medial root - medial cord of the brachial cord

course: laterally to the axillary artery, descends in the arm between biceps brachii and triceps brachii muscles, courses through the forearm with the ulna nerve and vessels before entering the carpal tunnel to the hand

major branches: anterior interosseous nerve, palmar cutaneous branch, motor branch in the hand

motor supply: flexor compartment of the foreman, thenar and intrinsic hand muscles

sensory supply: palmar aspect of the thumb, index, middle and radial half of the ring fingers

Anatomy

Origin

The median nerve is formed from a lateral root from the lateral cord and a medial root from the medial cord of the brachial plexus. It forms from nerve roots originating at C5-T1. 

Course

In the axilla, the median nerve lies lateral to the axillary artery. It enters the arm from axilla at the inferior margin of the teres major muscle and descends medially between biceps brachii and triceps brachii. 

In the cubital fossa, the median nerves lies medial to the brachial artery and the biceps brachii tendon. 

The median nerve enters the forearm between the two heads of pronator   teres muscle and gives off the anterior interosseous nerve. It courses towards the wrist with the ulnar nerve and ulnar vessels (deep to flexor digitorum superficialis) and enters the hand through the carpal tunnel (the only nerve to traverse the carpal tunnel), passes deep to the flexor retinaculum at the wrist. On entering the palm, it gives off motor and cutaneous branches. 

Branches

anterior interosseous nerve  - supplies all the flexor muscles of  the  forearm apart from flexor carpi ulnaris and  the ulnar half of flexor digitorum profundus

motor branch in the hand -  supplies thenar muscles and the radial two lumbricals

palmar cutaneous branch - cutaneous innervation to the palmar aspect of the thumb, index and middle fingers and the radial half of the ring finger

articular branches to the elbow, wrist, carpal and phalangeal joints

Variant anatomy high division or bifid median nerve

median nerve (normal or bifid) may be accompanied by a persistent median artery of the forearm

accessory branches arising proximal or distal to the carpal tunnel

variant course of thenar branch 5

Related pathology entrapment syndromes of the median nerve

o anterior interosseous nerve syndrome

o pronator teres syndrome

o carpal tunnel syndrome

Ulnar nerveDr Yuranga Weerakkody◉ and Dr Henry Knipe◉ et al.

The ulnar nerve is one of the terminal branches of the brachial plexus and has motor and sensory supply to the forearm and hand.

Gross anatomyOrigin

The ulnar nerve originates as a terminal branch of the medial cord of the brachial plexus with nerve root fibres from C8-T1.

Course

Arm

In the arm, the ulnar nerve runs medial to the axillary artery and subsequently the brachial artery on the coracobrachialis muscle in the anterior compartment.  The nerve passes to the posterior compartment through the medial intermuscular septum distally running with the superior ulnar collateral artery. Further on, it runs between medial head of triceps brachii muscle and the medial intermuscular septum to pass posterior to the medial humeral epicondyle in the superficial condylar groove (cubital tunnel).

Forearm

The ulnar nerve enters the forearm from the arm via the two heads of flexor carpi ulnaris (FCU) muscle. It subsequently lies superficial to flexor digitorum profundus and deep to FCU and medial to the ulnar artery.  At the wrist, the ulnar nerve runs lateral to the tendon of FCU,

Hand

The ulnar nerve enters the hand superficial to the flexor retinaculum and inside Guyon's canal. Then it divides into its terminal branches at the level of the pisiform bone.

Prior to passing the flexor retinaculum at the wrist, the ulnar nerve gives off the dorsal cutaneous branch. 

BranchesTerminal branches

palmar cutaneous branch

branch to palmaris brevis

superficial terminal branch

deep terminal branch

SupplyThe ulnar nerve has both sensory and motor supply:

motor - forearm flexors, intrinsic hand muscles

sensory -

o articular innervation to elbow, wrist, carpal and phalangeal joints

o cutaneous innervation to ulnar aspect of the hand, 5th finger, medial 4th finger

Related pathology ulnar nerve impingement

o cubital tunnel syndrome

Flexor carpi ulnarisDr Tim Luijkx and Dr Henry Knipe◉ et al.

Flexor carpis ulnaris (FCU) is a muscle of the first layer of the anterior compartment of the forearm.

Summary origin

o humeral head: medial epicondyle of the humerus

o ulnar head: olecranon of the ulna

insertion: base of 5th metacarpal; hook of hamate, piriformis

innervation: ulna nerve (C8-T1)

action: flexion and abduction of the wrist joint

Palmaris longusDr Henry Knipe◉ et al.

Palmaris longus is a superifical, weak flexor of the wrist located in the anterior compartment of the forearm.

Palmaris longus is often absent, more commonly unilaterally absent than bilaterally. There is ethnic variation in prevalence of absence:

absence in ~3% of Asians

absence in ~5% of African-Americans

absence in ~12-16% of Whites (Caucasians and Hispanics)

Due to its long tendon and short muscle belly, palmaris longus is often used as a donor tendon and its absence is not associated with any functional deficit 2.

Summary origin - medial epicondlye of the humerus

insertion - palmar aponeurosis

innervation - median nerve

action - weak flexor of the wrist and elbow; tightens palmar aponeurosis during power grip

Flexor digitorum superficialisDr Tim Luijkx and Dr Henry Knipe◉ et al.

Flexor digitorum superficialis (FDS) is a muscle in the second layer of the anterior compartment of the forearm that splits into four tendons, passes under theflexor   retinaculum  and through the carpal tunnel, to insert into the middle phalanx of the 2nd-4th digits. 

Summary origin

o humeroulnar head: medial epicondyle of the humerus  and coronoid process of the ulna

o radial head: diaphysis of the radius

insertion: via four tendons into the volar aspect of the middle phalanges of digits 2-4 (index, middle, ring and little fingers)

innervation: median nerve (C7-T1)

action: flexion of the proximal interphalangel joint

Flexor digitorum profundusDr Tim Luijkx and Dr Henry Knipe◉ et al.

Flexor digitorum profundus (FDP) makes up the third layer of the anterior compartment of the forearm along with flexor pollicis longus.

Summary origin: proximal, anterior surface of ulna and adjacent interosseous membrane

insertion: volar surface of distal phalanges 2-5 

innervation

o ulna part (third and fourth digits): ulnar nerve

o radial part (second and third digits): median nerve

action: flexion at the distal interphalangeal, proximal interphalangeal and wristjoints

Flexor pollicis longusDr Tim Luijkx and Dr Henry Knipe◉ et al.

Flexor pollicis longus (FPL) is one of the two muscles that make up the third layer of the anterior compartment of the forearm along with the flexor digitorum profundus. It is a deep muscle under abductor pollicis brevis muscle.

Summary origin: mid-anterior surface of the radial shaft and adjacent interosseous membrane; frequently

the FPL arises from the lower part and slip of coronoid process of ulna by a rounded bundle of muscular fibers and even medial epicondyle of humerus

insertion: volar surface of the distal 1st phalanx (thumb)

innervation: median nerve (C6-C7)

action: flexion of 1st interphalangeal joint

Pronator quadratusDr Tim Luijkx and Dr Henry Knipe◉ et al.

Pronator quadratus is the most distal muscle that makes up the fourth layer of the anterior compartment of the forearm.

Summary 

origin: anterior surface of distal quarter of ulnar shaft

insertion: anterior surface of distal quarter of radial shaft

innervation: median nerve (C7-T1)

action: pronates forearm

Posterior compartment of the forearmDr Henry Knipe◉ et al.

The posterior compartment of the forearm is divided from the anterior compartment of the forearm by deep fascia, the lateral deep intermuscular septum and the interosseous membrane between the radius and the ulna. 

MusclesThe posterior compartment of the forearm contains 11 muscles, divided into deep and superficial layers.

Superficial

brachioradialis

extensor carpi radialis longus

extensor carpi radialis brevis

extensor digitorum

extensor digiti minimi

extensor carpi ulnaris

Deep

supinator

extensor pollicis longus

extensor pollicis brevis

abductor pollicis longus

extensor indicis

The anconeus   is sometimes considered part of the posterior compartment of the forearm rather than part of the posterior compartment of the arm.

Blood supply arterial supply - anterior and posterior interosseous arteries (branches of theulna artery via the

common ulna artery)

Nerve supply all muscles in the extensor compartment are supplied by the radial nerve