WINDSOR UNIVERSITY SCHOOL OF MEDICINE St.Kitts DEPARTMENT OF ANATOMY UPPER LIMB FOREARM Dr. SREEKANTH THOTA

FOREARM The forearm is the part of the upper limb that extends between the elbow joint and the wrist joint. As in the arm, the forearm is divided into anterior and posterior compartments

Compartments of forearm Muscles in the anterior compartment of the forearm flex the wrist and digits and pronate the hand. Muscles in the posterior compartment extend the wrist and digits and supinate the hand.

ANTERIOR COMPARTMENT OF THE FOREARM Muscles in the anterior (flexor) compartment of the forearm occur in three layers: 1. Superficial 2. Intermediate 3.Deep All muscles in the anterior compartment of the forearm are innervated by the median nerve, except for the flexor carpi ulnaris muscle and the medial half of the flexor digitorum profundus muscle, which are innervated by the ulnar nerve.

Superficial layer Four muscles in the superficial layer- 1.flexor carpi ulnaris 2.palmaris longus 3.flexor carpi radialis 4. pronator teres- All four muscles have a common origin from the medial epicondyle of the humerus, and, except for pronator teres, extend distally from the forearm into the hand

Intermediate layer Flexor digitorum superficialis

Deep layer 1.flexor digitorum profundus 2.flexor pollicis longus 3.pronator quadratus

Anterior Forearm Pronator Teres Pronates and flexes forearm at the elbow Flexor Carpi Radialis Flexes and abducts hand (at the wrist) Palmarus Longus Flexes hand at the wrist and tightens palmar aponeurosis Ulnaris Flexes and adducts hand at the wrist

Flexor Digitorum Superficialis Flexor Digitorum Profundus Flexes middle phalanges at the proximal interphalangeal joints of medial four digits; acting more strongly, it also flexes proximal phalanges at metacarpophalangeal joints and hand[wrist] Flexor Digitorum Profundus Flexes distal phalanges at distal interphalangeal joints of medial four digits; assist with flexion of hand Flexor pollicis Longus Flexes 1st digit (thumb) Pronator Quadratus Pronates forearm; deep fibers bind radius and ulna together

Arteries of the anterior compartment of the forearm. At the apex of the cubital fossa, Brachial artery divides into its two major branches, the radial and ulnar arteries.

Radial artery In the distal forearm, the radial artery can be located using the flexor carpi radialis muscle as a landmark. Radial artery lies immediately lateral to the large tendon of the flexor carpi radialis muscle.

Radial pulse The radial pulse can be felt by gently palpating the radial artery against the underlying muscle and bone.

Nerves Nerves in the anterior compartment of the forearm are the median and ulnar nerves, and the superficial branch of the radial nerve.

Median nerve The median nerve innervates the muscles in the anterior compartment of the forearm except for the flexor carpi ulnaris and the medial part of the flexor digitorum profundus (ring and little fingers). It leaves the forearm and enters the palm of the hand by passing through the carpal tunnel deep to the flexor retinaculum.

Branches of median nerve 1. Anterior interosseous nerve: innervates the muscles in the deep layer 2. A small palmar branch originates from the median nerve in the distal forearm immediately proximal to the flexor retinaculum. Innervates the skin over the base and central palm. This palmar branch is spared in carpal tunnel syndrome because it passes into the hand superficial to the flexor retinaculum of the wrist.

Cutaneous branches of median and ulnar nerve

Ulnar nerve In the forearm, the ulnar nerve innervates only the flexor carpi ulnaris muscle and the medial part (ring and little fingers) of the flexor digitorum profundus muscle. Branches in forearm: 1.Palmar branch originates in the middle of the forearm and passes into the hand to supply skin on the medial side of the palm

Radial nerve The radial nerve bifurcates into deep and superficial branches under the margin of the brachioradialis muscle in the lateral border of the cubital fossa. The deep branch is predominantly motor and passes between the two heads of the supinator muscle to access and supply muscles in the posterior compartment of the forearm. The superficial branch of the radial nerve is sensory.

POSTERIOR COMPARTMENT OF THE FOREARM

POSTERIOR COMPARTMENT OF THE FOREARM Muscles in the posterior compartment of the forearm occur in two layers: 1.Superficial 2.Deep layer The muscles are associated with: 1.Movement of the wrist joint 2.Extension of the fingers and thumb 3.Supination. All muscles in the posterior compartment of the forearm are innervated by the radial nerve.

Superficial layer Seven muscles 1.Brachioradialis 2.Extensor carpi radialis longus 3.Extensor carpi radialis brevis 4.Extensor digitorum 5.Extensor digiti minimi 6.Extensor carpi ulnaris 7.Anconeus

Posterior view

Brachoradialis The brachioradialis is a paradoxical muscle. Its origin and innervation are characteristic of a extensor muscle, but it is actually a flexor at the elbow. The muscle is most visible when the forearm is half pronated, and flexing at the elbow against resistance. In the distal forearm, the radial artery and nerve are sandwiched between the brachioradialis and the deep flexor muscles. Attachments: Originates from the proximal aspect of the lateral supraepicondylar ridge of humerus, and attaches to the distal end of the radius, just before the radial styloid process. Actions: Flexes Forearm(weak) Innervation: Radial nerve.

Brachioradialis

Extensor Carpi Radialis Longus and Brevis The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm. Due to their position, they are able to produce abduction as well as extension at the wrist. Attachments: The ECRL originates from the supracondylar ridge, while the ECRB originates from the lateral epicondyle. Their tendons attach to metacarpal bones II and III. Actions: Extends and abducts the wrist. Innervation: Radial nerve.

Extensor carpi radialis longus and brevis

Extensor Digitorum The extensor digitorum is the main extensor of the fingers. To test the function of the muscle, the forearm is pronated, and the fingers extended against resistance. Attachments: Originates from the lateral epicondyle. The tendon continues into in the distal part of the forearm, where it splits into four, and inserts into the extensor expansion of each finger. Actions: Extends medial four fingers at the MCP and IP joints. Innervation: Radial nerve.

Extensor digitorum

Extensor Digiti Minimi The extensor digiti minimi is thought to originate from the extensor digitorum muscle. In some people, these two muscles are fused together. Anatomically, the extensor digiti minimi lies medially to the extensor digitorum. Attachments: Originates from the lateral epicondyle of the humerus. It attaches, with the extensor digitorum tendon, into the extensor expansion of the little finger. Actions: Extends the little finger, and contributes to extension at the wrist. Innervation: Radial nerve.

Extensor digiti minimi

Extensor Carpi Ulnaris The extensor carpi ulnaris is located on the medial aspect of the posterior forearm. Due to its position, it is able to produce adduction as well as extension at the wrist. Attachments: Originates from the lateral epicondyle of the humerus, and attaches to the base of metacarpal V. Actions: Extension and adduction of wrist. Innervation: Radial nerve.

Tennis elbow(Lateral epicondylitis) It occurs at the common extensor tendon that originates from the lateral epicondyle. The acute pain that a person might feel occurs as one fully extends the arm.

Deep layer Five muscles 1-Supinator 2-Abductor pollicis longus 3-Extensor pollicis brevis 4-Extensor pollicis longus 5-Extensor indicis

Supinator The supinator lies in the floor of the cubital fossa. It has two heads, which the deep branch of the radial nerve passes between. Attachments: It has two heads of origin. One originates from the lateral epicondyle of the humerus, the other from the posterior surface of the ulna. They insert together into the posterior surface of the radius. Actions: Supinates the forearm. Innervation: Radial nerve.

Abductor Pollicis Longus The abductor pollicis longus is situated immediately distal to the supinator muscle. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox. Attachments: Originates from the interosseous membrane and the adjacent posterior surfaces of the radius and ulna. It attaches to the base of 1st metacarpal . Actions: Abducts the thumb. Innervation: Radial nerve.

Extensor Pollicis Longus & Brevis The tendon of the Extensor pollicis longus forms the medial border of the anatomical snuffbox in the hand. Attachments: Originates from the posterior surface of the ulna and interosseous membrane. It attaches to the base of the distal phalanx of the thumb. Actions: Extends distal phalanx of thumb at IP joint The Extensor pollicis brevis contributes to the lateral border of the anatomical snuffbox. Attachments: Originates from the posterior surface of the radius and interosseous membrane. It attaches to the base of the proximal phalanx of the thumb. Actions: Extends proximal phalanx of thumb at MCP joint Innervation for both: Radial nerve.

Extensor Indicis This muscle allows the index finger to be independent of the other fingers during extension. Attachments: Originates from the posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus. Attaches to the extensor expansion of the index finger. Actions: Extends the index finger &helps extend hand at wrist. Innervation: Radial nerve.

Extensor indicis

ANATOMICAL SNUFFBOX

ANATOMICAL SNUFFBOX Boundries Medially -Extensor pollicis longus tendon Laterally Abductor pollicis longus tendon Extensor pollicis brevis tendon Clinical importance 1- Scaphoid bone 2- Radial pulsation

Radial nerve The nerve of the posterior compartment of the forearm is the radial nerve . In the lateral wall of the cubital fossa, and before dividing into superficial and deep branches, the radial nerve innervates the brachioradialis and extensor carpi radialis longus muscles. Posterior interosseous nerve supplies the remaining muscles in the posterior compartment.

Posterior interosseous nerve

Radial Nerve Injury in the Forearm Injury to the deep branch of the radial nerve may occur when wounds of the forearm are deep (penetrating). Severance of the deep branch of the radial nerve results in an inability to extend the thumb and the metacarpophalangeal (MP) joints of the other digits.

Testing the radial nerve Integrity of the deep radial nerve may be tested by asking the person to extend the MP joints while the examiner provides resistance