Muscles of the Posterior Forearm Flashcards
What are the muscles in the posterior compartment of the forearm commonly known as?
The extensor muscles
What is the general function of the muscles of the posterior compartment of the forearm?
To produce extension at the wrist and fingers
What are the extensor muscles innervated by?
The radial nerve
What can the muscles of the posterior forearm be divided into?
Two layers, deep and superficial
What divides the layers of muscles in the posterior forearm?
A layer of fascia
How many muscles are in the superficial layer of the posterior forearm?
6
What are the muscles of the superficial layer of the posterior forearm?
Brachioradialis Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris
What muscles share a common tendinous origin at the lateral epicondyle?
Extensor carpi radialis longus
Extensor digitorum
Extensor digiti minimi
Extensor carpi ulnaris
Why is the brachioradialis a paradoxical muscle?
Because its origin and innervation are characteristic of an extensor muscle, but its actually a flexor at the elbow
When is the brachioradialis most visible?
When the forearm is half pronated, and flexing elbow against resistance
Where are the radial artery and nerve found in the distal forearm?
Sandwiched between the brachioradialis and the deep flexor muscles
What is the innervation of the brachioradialis?
Radial nerve (C5, C6, C7)
What is the arterial supply of the brachioradialis?
Radial recurrent artery
What is the main action of the brachioradialis?
Relatively weak flexion of the forearm, maximal when the forearm is in mid-pronated position
Where are the extensor carpi radialis muscles situated?
On the lateral aspect of the posterior forearm
What are the extensor carpi radialis muscles able to do due to their position?
Produce abduction as well as extension at the wrist
What is the innervation of the ECRL?
Radial nerve (C6, C7)
What is the arterial supply of the ECRL?
Radial artery
What is the innervation of the ECRB?
Deep branch of radial nerve (C7, C8)
What is the arterial supply of the ECRB?
Radial artery
What is the main action of the extensor carpi radialis muscles?
Extend and abduct the hand at the wrist joint
ECRL active during fist clenching
How is the function of the extensor digitorum tested?
The forearm is pronated, and the fingers extended against resistance
What is the innervation of the extensor digitorum?
Deep branch of radial nerve (C7, C8)
What is the arterial supply of the extensor digitorum?
Recurrent interosseous artery
Posterior interosseous artery
What is the action of the extensor digitorum?
Extends medial four digits primarily at metacarpophalangeal joints, secondarily at interphalangeal joints
What is true in some people regarding the extensor digiti minimi?
This muscle and the extensor digitorum muscle are fused together
Where does the extensor digiti minimi (EDM) lie?
Medially to the extensor digitorum
What is the innervation of the EDM?
Deep branch of radial nerve (C7, C8)
What is the arterial supply of the EDM?
Posterior interosseous artery
What is the main action of the EDM?
Extends 5th digit primarily at metacarpophalangeal joint, secondarily at interphalangeal joint
Where is the extensor carpi ulnaris (EDU) found?
On the medial aspect of the posterior forearm
What is the EDU able to do due to its position?
Produce adduction as well as extension at the wrist
What is the innervation of the ECU?
Deep branch of the radial nerve (C7, C8)
What is the arterial supply of the ECU?
Ulnar artery
What is the main action of the ECU?
Extends and adducts the hand at the wrist joint
Active during fist clenching
What does lateral epicondylitis refer to?
Inflammation of the periosteum of the lateral epicondyle
What is the peak age of onset of lateral epicondylitis?
40-50 years
What is lateral epicondylitis caused by?
Repeated use of the superficial extensor muscles, which stains their common tendinous attachment of the lateral epicondyle
How many muscles are in the deep compartment of the posterior forearm?
5
What muscles are in the deep compartment of the posterior forearm?
Supinator Abductor pollicis longus Extensor pollicis brevis Extensor pollicis longus Extensor indicis
What do the deep muscles of the posterior forearm do?
Act on the thumb and index finger, with the exception of the supinator
Where does the supinator lie?
On the floor of the cubital fossa
What does the supinator have?
Two heads
What passes between the two heads of the supinator?
The deep branch of the radial nerve
What is the innervation of the supinator?
Deep branch of radial nerve (C7, C8)
What is the arterial supply to the supinator?
Recurrent interosseous artery
What is the main action of the supinator?
Supinates forearm- rotates radius to turn palm anteriorly or superiorly (if elbow are flexed)
Where is the abductor pollicis longus?
Immediately distal to the supinator muscle
What does the tendon of the abdutor pollicis longus contribute to?
The lateral border of the anatomical snuffbox
What is the innervation of the APL?
Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve
What is the arterial supply of the APL?
Posterior interosseous artery
What is the main action of the APL?
Abducts the thumb and extends it at the carpometacarpal joint
Where can the extensor pollicis brevis be found?
Medially and deep to the abductor pollicis longus
What does the tendon of the EPB contribute to?
The lateral border of the anatomical snuffbox
What is the innervation of the EPB?
Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve
What is the arterial supply of the EPB?
Posterior interosseous artery
What is the main action of the EPB?
Extends proximal phalanx of thumb at metacarpophalgeal joint
Extends carpometacarpal joint
How does the extensor pollicis longus different from the EPB?
It has a larger muscle belly
Where does the tendon of the EPL travel?
Medially to the dorsal tubercle at the wrist
What does the tendon of the EPL act to do?
Uses the dorsal tubercle as a ‘pulley’ to increase the force exerted
What does the tendon of the EPL form?
The medial border of the anatomical snuffbox
What is the innervation of the EPL?
Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve
What is the arterial supply of the EPL?
Posterior interosseous artery
What is the main action of the EPL?
Extends distal phalanx of thumb at interphalangeal joints
Extends metacarpophalangeal and carpometacarpal joints
What does the extensor indicis proprius allow?
The index finger to be independent of the other fingers during extension
What is the innervation of the EIP?
Posterior interosseous nerve (C7, C8), a continuation of the deep branch of the radial nerve
What is the arterial supply of the EIP?
Posterior interosseous artery
What is the main action of the EIP?
Extends 2nd digit (enabling independent extension)
Helps extend hand at wrist
What is wrist drop a sign of?
Radial nerve injury that has occurred proximal to the elbow
What are the common characteristic sites of damage with wrist drop?
Axilla
Radial groove of humerus
What causes wrist drop?
The radial nerve innervates all muscles in the extensor compartment of the forearm. In the event of a radial nerve lesion, these muscles areparalysed. The muscles that flex the wrist are innervated by themedian nerve, and thus are unaffected. The tone of the flexor muscles produces unopposed flexion at the wrist joint – wrist drop.
