Forearm and Hand

Anterior aspect of forearm-Superficial muscles –All of them originate from medial epicondyle of the humerus.

a) Pronator teres – Inserts to lateral surface of radius. Pronator of forearm.

b)Flexor carpi radialis – inserts into base of 2nd and 3rd metacarpal bones. Flexor of the wrist.

c) Palmaris longus – inserts into distal half of flexor retinaculum and apex of palmar aponeurosis. Flexor of the wrist. Can tense the palmar aponeurosis.

d)Flexor carpi ulnaris – inserts to base of 5th

metacarpal bone. Flexor of the wrist and an adductor of the wrist.

e) Flexor digitorum superficialis – It ends in 4 tendons. One for each of the four medial fingers. Inserted onto the middle phalanx. Flexor of the wrist, MPJ, PIPJ.

All are supplied by medial nerve, except flexor carpi ulnaris, which is supplied by ulnar nerve.

Deep muscles –a)Flexor digitorum profundus – Powerful bulky muscle of forearm. Has 4 tendons. Origin is from ulnar bone and interosseous membrane. Inserts onto base of distal phalanx. Flexor of the DIP, PIP, MPJ and wrist.

b)Flexor policis longus- origin from radius bone and interosseous membrane. Inserts onto distal phalanx of the thumb. Flexor of the distal phalanx of the thumb.

c) Pronator quadratus – Origin from shaft of ulnar lower ¼. Inserts into anterior border of radius. It is a pronator of the forearm.

FPL. PQ and lateral ½ of FDP are supplied by anterior interosseous branch of median nerve. Medial ½ of FDP is supplied by ulnar nerve.

Posterior aspect of forearm-Superficial muscles –They originate from lateral epicondyle of the humerus.

a) Anconeus – Inserts onto ulnar. Week extensor of elbow. Nerve -Radial

b)Brachioradialis – Inserts onto lateral side of radius. Supinates pronated forearm. Pronates supinated forearm. Nerve- Radial

c) Extensor carpi radialis longus – Inserts onto base of 2nd metacarpal bone. Extensor of wrist, abductor of wrist. Nerve - Radial

d)Extensor carpi radialis brevis – Bases of 2nd and 3rd metacarpal bones. Nerve – posterior interosseous nerve. Extensor of wrist.

e) Extensor digitorum – Tendon of muscle splits into 4 parts and inserts into 4 medial fingers. Tendon for each digit divides into 3 slips. Intermediate slip to the base of middle phalanx. Collateral slips

unite and inserted onto the base of distal phalanx. Nerve – posterior interossseous nerve. Extensor of IPJ, MPJ and wrist joints.

f) Extensor digiti minimi – Inserts into base of middle and distal phalanx of 5th digit. Nerve – posterior interosseous nerve. Extensor of IPJ, MPJ and wrist.

g) Extensor carpi ulnaris - Inserts onto base of medial side of fifth metacarpal bone. Nerve – posterior interosseous nerve. Extensor and adductor of the wrist.

Deep muscles –

Supinator – origin from humerus and ulnar. Inserts onto radius. Supinates the forearm.

Abductor pollicis longus – origin from ulnar, radius and interosseous membrane. Inserts onto lateral side of base of first metacarpal. Abductor and an extensor of the thumb.

Extensor pollicis longus – origin from ulnar and interosseous membrane. Inserts onto base of distal phalanx of the thumb. Helps in extension of the thumb in all joints.

Extensor pollicis brevis – origin from radius and interosseous membrane. Inserts into base of proximal phalanx. Extends the proximal phalanx.

Extensor indicis – origin from ulnar and interosseous membrane. Inserts by joining the tendon of extensor digitorum. Extensor of index finger.Nerve supply is by posterior interosseous nerve.

Extensor indicis and extensor digiti minimi reinforces the extensor digitorum longus on the medial side.Extensor tendons are inserted into the base of proximal phalanx. From this insertion tendons spread distally as the extensor expansion, which is attached by a central slip to the middle phalanx and by two lateral slips to the distal phalanx.

Intrinsic muscles of the hand-a) Dorsal and palmar interossei – They arise from

sides and fronts of metacarpals respectively.b)Lumbricals – Arise from flexor tendons.

These muscles which arising from palmar aspect of the hand and inserted along the dorsal aspect of the fingers flex the MPJ and extend the IPJ.Palmar interossei causes adduction of the fingers (PAD). Dorsal interossei causes abduction of the fingers (DAB).

The fifth finger of the hand receive two further intrinsic muscles. They’re the flexor digiti minimi and opponens digiti minimi. These muscles form the hypothenar eminence. These muscles origin from hook of hamate and flexor retinaculum and are supplied by ulnar nerve.

Muscles acting on the thumb-Long muscles- FPL – inserted into distal phalanx.EPL – inserted into the distal phalanx.EPB – inserted into the proximal phalanx.APL – inserted into the metacarpal.

Elbow joint –Synovial joint.Articular surfaces –Capitulum of humerus – radial head – ball and socketTrochlear of humerus - trochlear notch of ulnar – hinge jointHead of radius – radial notch of ulnar – pivot joint.Capsule – Attached around articular surfaces. Thin anteriorly and posteriorly to allow flexion and extension. Thickened on either side to form the medial and lateral collateral ligaments.

Movements –Flexion and extension at humero-ulnar and humero-radial joints.Flexion – biceps, brachialis, brachioradialis and forearm flexor muscles.Extension – triceps, anconeus

Pronation and supination at the proximal radio ulnar joint.Pronators – pronator teres, pronator quadratus, flexor carpi radialisSupinators – supinator, biceps, extensor pollicis longus, abductor pollicis longus.

Short muscles of the hand-Adductor pollicis (AP) – inserted into base of proximal phalanx. Origin – capitate and 2nd and 3rd metacarpal bones.Flexor pollicis brevis (FPB)- inserted into base of proximal phalanx. Origin – trapezium, flexor retinaculum, trapezoidAbductor pollicis brevis(APB)- inserted into base of proximal phalanx. Origin – scaphoid, trapezium and flexor retinaculum.Opponens pollicis(OP) – inserted to the first metacarpal. Origin from trapezium and flexor retinaculum. These muscles are called the muscles of thenar eminence. All of them are supplied by median nerve except the adductor pollicis.All intrinsic muscles of the hand are supplied by ulnar nerve except the radial two lumbricals and FPB, APB and OP.

Arrangement of structures in palmar aspect of hand-Skin – Thick, immobile and creased. Supplied by spinal nerves C6,7,8.Superficial fascia – Has dense fibrous bands, which binds skin to the deep fascia. These divide subcutaneous fat into small tight compartments.Deep fascia – Is specialized to form flexor retinaculum, palmar aponeurosis and fibrous flexor sheaths in the tendons.

Flexor retinaculum – It is a strong fibrous band, which bridges the anterior concavity of the carpus and converts it into a tunnel.Medial attachments – pisiform and hook of hamate. Lateral attachments – scaphoid and trapezium.Structures passing superficial to it – Palmaris longus, palmar cutaneous branches of median and ulnar nerves, ulnar nerve and vessels.Structures passing deep to it – median nerve, tendons of FDS, FDP, FPL, FCR ulnar and radial bursae.Applied anatomy -Surface marking is important.Carpal tunnel syndrome – This syndrome consists of sensory and motor symptoms caused by compression of median nerve in the carpal tunnel. Causes could be arthritis of wrist, fracture or dislocation of lunate, myxoedema, acromegaly, obesity etc.

Palmar aponeurosis – It is a part of deep fascia. Triangular in shape. Apex blends with the flexor retinaculum. Base is directed distally. Opposite the heads of metacarpals of four medial fingers it divides into four slips. Each slip divides into two parts and are continuous with fibrous flexor sheaths. It is attached to the sides of proximal and middle phalanges. Digital vessels, nerves and lumbricals emerge through the interval between the slips. From the lateral and medial margins of palmar aponeurosis, the lateral and medial palmar septa passes backwards and divide the palm into compartments. Function – Fixes the skin of palm and improves the grip. Protects underlying tendon vessels and nerves. Applied anatomy –Duputrens contracture – results from fibrous contraction of the palmar fascia, particularly of the 4th

and 5th fingers. Contracture of this fascia results in longitudinal thickening in the palm together with flexion of MPJ and PIPJ.

Fibrous flexor sheaths of the fingers –Made up of deep fascia. They are thick and arched. Attached to the sides of phalanges and across the base of distal phalanx. Proximally it is continuous with a slip of palmar aponeurosis. These are thick opposite the phalanges and thin opposite the joints to permit free flexion. This osteofascial tunnel contains a long flexor tendon enclosed in a digital synovial sheath. The sheath holds the tendons in position during flexion of the digits.

Extensor retinaculum – Formed by deep fascia on the back of the wrist. They hold the extensor tendons in place. It is an oblique band directed downwards and medially.Medial attachment – styloid process of ulnar, triquetral and pisiform.Lateral attachment – lower part of anterior border of radius.This sends fibrous septa to posterior surface of lower end of radius and form osteofascial compartments. Each compartment is lined by a synovial sheath, which, is reflected onto the contained tendons.APL, EPB – C1ECRL, ECRB – C2EPL – C3ED,EI, AI artery, PI nerve – C4EDM – C5ECU – C6

Spaces of the hand –Can get infected and distended with pus and cause pain.

a) Superficial pulp space of the fingers – Tips of fingers and thumb are composed entirely ofsubcutaneous fat broken up and packed betweenfibrous septa, which pass from the skin down to the periosteum of the terminal phalanx. The tightpacking of this compartment is responsible forsevere pain of a septic finger. Blood vessels to theshaft of the terminal phalanx traverse this space. Ateach of the skin creases of the fingers, the skin is bound down to the underlying flexor sheath so that

the pulp over each phalanx is in a separate compartment.

Infection of this space can cause thrombosis of blood vessels traversing this space and cause necrosis of diaphysis of the bone. Infection of one space can spread to another space along the neurovascular digital bundles.

b)Synovial tendon sheaths of the fingers – Fibrous sheaths of the fingers are lined by synovial membrane, which is reflected around each tendon. Tendons of 2nd, 3rd and 4th fingers have synovial sheaths which are closed off proximally at the metacarpal head. c) Radial bursa – This is the synovial sheath of the long flexor tendon of the thumb which, extend proximally through the palm deep to flexor retinaculum to about 2.5cm above the wrist.

d) Ulnar bursa – It is the synovial sheath of the fifth finger. It also extends proximally about 2.5cm above the wrist. In the palm it encloses all the finger tendons. It is an expanded synovial sheath.

In 50% of cases radial and ulnar bursae communicate. They can be infected by an entry of a splinter or from a neglected pulp space infection.

e) Mid palmar space – Lies posterior to flexor tendons and ulnar bursa in the hand and anterior to the 3rd, 4th and 5th

metacarpals with there attached interossei.

f) Thenar space – It is the space superficial to the 2nd and 3rd metacarpals and the adductor pollicis.

These spaces can get infected by a penetrating wound or from a long standing tendon sheath infection. Blood supply-

Radial artery –Commences at the radial neck by lying on biceps tendon. In the upper half it is overlapped by brachioradialis muscle. In the middle third of the forearm radial nerve lies along lateral side of the artery. Distally in the forearm it lies between brachioradialis and flexor carpi radialis. Distally to the radial pulse it gives off a branch to assist in the forming of superficial palmar arch. Then passes below tendons of anatomical snuff box and pierces the first dorsal interosseous muscle and adductor pollicis, between first and second metacarpals and form the deep palmar arch with the deep branch of ulnar artery.

Ulnar artery –Larger than radial artery. From its commencement it passes beneath the muscles of common flexor origin and

lies upon flexor digitorum profundus overlapped by flexor carpi ulnaris. At the beginning median nerve is separated from ulnar artery by the deep head of pronator teres muscle. In the distal two-thirds of the forearm ulnar nerve accompanies artery on its medial side. In the distal half of the forearm it becomes superficial between the tendons of flexor carpi ulnaris and tendons of flexor digitorum superficialis. It then crosses the flexor retinaculum and forms the superficial palmar arch with the superficial branch of radial artery. There is a rich anastomosis of arteries around all major joints.

Palpation of arterial pulses are important.

Veins of upper limb –Superficial veins –Dorsal venous network on back of the hand – lateral cephalic and medial basilic vein.

Cephalic vein – Posterior to radial styloid – anterior aspect of the forearm – lateral border of biceps – pierces the deep fascia in the groove between pectoralis major and deltoid – pierces the clavi pectoral fascia – axillary vein.

Basilic vein – Posterior medial aspect of forearm – anterior aspect just below the elbow – pierces the deep fascia at about

middle of the upper arm – edge of posterior axillary fold it is joined by venae comitantes of brachial artery to form the axillary vein.

Median cubital vein – Links cephalic and basilic veins just distal to the elbow. It lies on bicipital aponeurosis. Most prominent superficial vein in the body. Can be used in phlebotomy.

Deep vena comitantes accompany all main arteries in pairs.

Nerves of the forearm and Hand-

Radial nerve – C5,6,7,8T1Posterior cord – between long and medial heads of triceps – spiral groove on back of humerus between medial and lateral heads of triceps – lower third of humerus – pierces lateral intermuscular septum – anterior compartment of the arm – lies between brachialis and brachioradialis – lateral epicondyle – gives off posterior interosseous nerve which, winds around the radius within the supinator muscle and be distributed to extensor muscles of the forearm. Radial nerve – superficial radial nerve – deep to brachioradialis – above the wrist – emerges beneath the muscle – divides into cutaneous nerves to posterior aspect of radial three and a half digits.Radial nerve supplies – Triceps, anconeus brachioradialis and ECR.Posterior interosseous nerve –

Remaining extensor muscles , supinator and APLCutaneous supply – Back of arm, forearm, radial side of dorsum of the hand.Damage to radial nerve – Main trunk – wrist dropPosterior interosseous nerve – ECR is spared therefore wrist extension can be done.Cutaneous loss – dorsum of hand between 1st and 2nd

metacarpals.

Ulnar nerve – C7,8T1 Medial cord – medial to axillary and brachial – pierces medial intermuscular septum – descend on anterior face of triceps – passes posterior to medial epicondyle – enters the forearm – posterior to flexor carpi ulnaris – radial side of flexor carpi ulnaris tendon – about 5cm above the wrist gives off dorsal cutaneous branch to supply dorsal aspect of ulnar 1 ½ of fingers. – then crosses flexor retinaculum superficially – divide into superficial and deep terminal branches.Superficial terminal branch – anterior aspect of ulnar 1 ½ of fingers.Deep terminal branch – hypothenar muscles and intrinsic muscles of the hand.

Ulnar nerve supplies – FCU, medial ½ of FDP, hypothenar muscles, interossei, 3rd and 4th lumbricals and AP. Cutaneous supply to medial side both aspects of hand and 1 ½ fingers.Damage to ulnar nerve –Lacerations of wrist – claw hand, wasting of interosseiInjured at the elbow (medial epicondyle fracture) – radial deviation of wrist, clawing of 4th and 5th fingers will be less.When hand is laid flat on a surface abduction and adduction of the fingers will be lost.Sensory loss over ulnar side 1 ½ fingers.

Median nerve –Union of branches from medial and lateral cords anterior to third part of axillary artery – lateral aspect of brachial artery – mid humerus – crosses superficial to the artery to lie on its medial side – enters the forearm between two heads of pronator teres – gives off anterior interosseous branch and passes on the deep aspect of FDS attached to it – at the wrist lies on the medial side of FCR – passes deep to flexor retinaculum – hand. Median nerve supplies –All muscles on flexor aspect of forearm except FCU and medial ½ of FDP, thenar eminence, radial two lumbricals.Cutaneous supply – skin of radial side of palm, palmar and variable degree of dorsal aspect of radial 3 ½ digits.

Damage to medial nerve –Lacerations of the wrist – wasting of thenar muscles, loss of opponence of thumb, loss of sensation over thumb, adjacent radial 2 ½ fingers, radial 2/3 of palm of the hand.Divided at the elbow – Pronation of forearm is impaired, wrist flexion is weak and there is ulnar deviation.

Volkmann’s contracture – Ischaemia and subsequent fibrosis and contraction of long flexor and extensor muscles of forearm. There is flexion at the wrist, extension at MPJ and flexion at IPJ.