A3 - Forearm Flashcards
What are the bones of the forearm?
the radius and ulna
What are the 3 articulations of the radius and ulna?
- proximally with the humerus at the elbow joint
- proximally with each other at the superior (proximal) radioulnar joint
- distally with each other at the inferior (distal) radioulnar joint
What does the radius articulate with distally?
the carpal bones to form the radiocarpal joint (wrist)
What is the interosseous membrane and what does it connect?
it is a thin, fibrous sheet that connects the medial border of the radius and the lateral border of the ulna
Label the components of the forearm
Label the components of the radius and the ulna
What are the 2 movements possible at the superior/inferior radioulnar joints?
supination and pronation
What is supination?
the action of turning the palm up to face you
(the palm and the pads of the fingers are visible)
What is the main muscle involved in supination of the forearm?
Supinator - this is a posterior forearm muscle
What is the second muscle involved in supination of the forearm?
Biceps brachii - an anterior arm muscle
using biceps increases the power of supination when the elbow is flexed
What is pronation?
the act of turning your palm down to face the ground
e.g. when typing at a keyboard
What are the 2 anterior forearm muscles involved in pronation?
- pronator teres
- pronator quadratus
Label the muscles involved in supination and pronation
Where is supinator located?
What is its origin?
It is in the posterior compartment of the forearm
It originates from:
- supinator crest of the ulna
- lateral epicondyle of the humerus
- ligaments associated with the elbow joint
What is the insertion of supinator?
it attaches to the shaft of the radius superior to the oblique line
Where are pronator teres and pronator quadratus located?
in the anterior compartment of the forearm
What is the origin and insertion of the pronator teres?
it runs from the medial epicondyle of the humerus to midway along the lateral surface of the radius
What is the insertion and the origin of the pronator quadratus?
It extends between the anterior surfaces of the distal ends of the radius and ulna
Label the 3 muscles involved in supination and pronation
Why is the cubital (antecubital) fossa clinically important?
- it contains several important neurovascular structures
- superficial veins overlying the cubital fossa are routinely used for venepuncture and intravenous cannulation
What are the 3 main contents of the cubital fossa?
- tendon of biceps brachii muscle
- brachial artery
- median nerve
What is the superior border of the cubital fossa?
a hypothetical line between the medial and lateral epicondyles of the humerus
What is the lateral border of the cubital fossa?
medial border of brachioradialis muscle
What is the medial border of the cubital fossa formed from?
lateral border of the pronator teres muscle
What forms the floor of the cubital fossa?
brachialis muscle
Label the borders of the cubital fossa
Label the muscles, arteries and nerves surrounding the antecubital fossa
At the level of the cubital fossa, which artery bifurcates?
What does it split into?
The brachial artery bifurcates into the radial and ulnar arteries
Label the vessels and nerves
Why must care be taken when inserting a needle into one of the superficial veins of the cubital fossa?
the brachial artery and the median nerve lie deeper than the superficial veins
How do the superficial veins drain the upper limb?
the basilic vein joins with the brachial vein to form the axillary vein
the cephalic vein drains into the axillary vein
as it passes under the clavicle, it becomes the subclavian vein
How can the muscles of the anterior compartment of the forearm be divided into 3 groups?
- superficial
- intermediate
- deep
What are the superficial muscles of the anterior compartment of the forearm?
- flexor carpi radialis
- flexor carpi ulnaris
- palmaris longus
- pronator teres
What are the deep muscles of the anterior compartment of the forearm?
- flexor digitorum profundus
- flexor pollicis longus
- pronator quadratus
What are the intermediate muscles of the anterior compartment of the forearm?
flexor digitorum superficialis
What is the alternative name for the anterior compartment of the forearm?
flexor compartment
all the muscles flex the wrist, fingers and thumb
Where is the common flexor origin?
What is significant about it?
all of the superficial flexors arise from the common flexor origin
this is the medial epicondyle of the humerus
Label the superficial flexors of the forearm
- flexor carpi ulnaris
- palmaris longus
- flexor carpi radialis
- pronator teres
Identify the locations of the 4 superficial flexors
What is the role of pronator teres?
it is a pronator and a weak flexor of the forearm
What is the function of flexor carpi radialis and flexor carpi ulnaris?
They both flex the wrist
FCR ABducts the wrist
FCU ADducts the wrist
What is the function of palmaris longus?
It flexes the wrist
What are the innervations of the superficial flexors?
FCU is innervated by the ulnar nerve
FCR, PL and PT are innervated by the median nerve
What are the distal insertions of palmaris longus and pronator teres?
PL - palmar aponeurosis of the hand
PT - lateral surface of midshaft of radius
What are the distal insertions of flexor carpi radialis and flexor carpi ulnaris?
FCR - base of metacarpals II and III
FCU - pisiform bone
Label the 4 superficial flexors of the forearm
What does the flexor digitorum superficialis give rise to?
it gives rise to 4 tendons
these travel through the carpal tunnel and under the flexor retinaculum and into the 4 fingers
Why are the distal insertions of the FDS tendons clinically important?
- essential for normal function of the fingers and hand
- vulnerable when the hand and/or fingers are injured
What happens to the FDS tendons at the base of the proximal phalanx?
the tendon of the FDS splits into 2 parts
these ultimately attach to the margins of the middle phalanx
What does flexor digitorum superficialis flex?
the metacarpophalangeal joint and proximal interphalangeal joint of each finger
(and the wrist joint)
What is flexor digitorum superficialis innervated by?
the median nerve
Where do the deep flexors of the arm originate from?
the shaft of the radius and ulna and the interosseous membrane
Where do the tendons of FDP insert?
the distal phalanges of the 4 fingers
What does FDP flex?
the distal interphalangeal joints of the fingers
(as well as the metacarpophalangeal joints of the fingers and the wrist joint)
What is the innervation of FDP?
Lateral half:
median nerve
Medial half:
ulnar nerve
What nerves innervate the flexors of the forearm?
FCU and the medial half of FDP are innervated by ulnar nerve
All the others are innervated by the anterior interosseous nerve (branch of median nerve)
What is the role of flexor pollicus longus?
it flexes the interphalangeal joint and metacarpophalangeal joint of the thumb
Label the muscles of the anterior compartment
Label the muscles of the anterior compartment
Where does pronator quadratus insert?
What is its role?
distal anterior surface of the radius
it is involved in pronation of the forearm
What is an alternative name for the muscles of the posterior forearm?
the “extensor compartment”
this is divided into superficial and deep extensors
What are the 5 superficial extensors of the forearm?
- extensor carpi radialis longus (ECRL)
- extensor carpi radialis brevis (ECRB)
- extensor digitorum (ED)
- extensor carpi ulnaris (ECU)
- extensor digiti minimi (EDM)
Where is the common extensor origin?
most of the superficial extensors originate from the lateral epicondyle of the humerus
Which of the superficial extensors are the principal extensors of the wrist?
- extensor carpi radialis brevis
- extensor carpi radialis longus
- extensor carpi ulnaris
Label the superficial extensors of the forearm
What nerves innervate the superficial extensors of the forearm?
posterior interosseous nerve:
- extensor carpi ulnaris
- extensor digiti minimi
- extensor digitorum
deep branch of radial nerve:
- extensor carpi radialis brevis
radial nerve:
- extensor carpi radialis longus
What is the insertion of extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB)?
ECRL:
dorsal surface of base of metacarpal II
ECRB:
dorsal surface of base of metacarpals II and III
What is the insertion of extensor digitorum?
4 tendons which insert via extensor hoods into the bases of middle and distal phalanges of the 4 fingers
What is the insertion of extensor digitorum minimi?
the extensor hood of the little finger
What is the insertion of extensor carpi ulnaris?
the tubercle on the base of the medial side of metacarpal V
Where do the tendons of extensor digitorum and extensor digiti minimi travel to?
Where do they insert?
ED gives rise to tendons that travel to digits 2-5
EDM tendon travels to digit 5
The tendons pass beneath the extensor retinaculum and insert onto the extensor expansion (or ‘hood’)
What is the role of the EDM and ED tendons?
When are they vulnerable?
They extend the wrist and fingers
They are vulnerable when the dorsal aspect of the hand and/or fingers are injured
What is the role of the extensor expansion (hood)?
It keeps the extensor tendons in the midline of the digits
It acts as an insertion point for the tendons of some of the small muscles in the hand
Label the components of the extensor hood
Where is brachioradialis found?
Where does it originate from and extend to?
it is a superficial posterior compartment muscle
it originates from the supracondylar ridge of the humerus
it extends to the distal radius
What is the role of brachioradialis?
it returns the forearm to the mid-prone position from either full supination or pronation
it contributes to flexion at the elbow joint
Why is brachioradialis NOT involved with flexion or extension of the wrist?
it does not cross the wrist joint
Which muscle is shown in the diagram?
brachioradialis
Where do the deep extensors of the forearm arise from?
the shaft of the radius and ulna and the interosseous membrane
What are the roles of the deep extensors of the forearm?
abduction and extension of the thumb
extension of the index finger
What are the 4 deep extensors of the forearm?
- extensor indicis (EI)
- extensor pollicis longus (EPI)
- extensor pollicis brevis (EPB)
- abductor pollicis longus (APL)
How would injury to the deep extensors affect movement of the hand?
Injury to the EI tendon would affect movement and function of the index finger
Injury to the EPL, EPB or APL tendons would impair movement and function of the thumb
What nerves innervate the deep extensors of the forearm?
They are all innervated by the posterior interosseous nerve
Label the deep extensors of the forearm
What is the distal insertion and action of extensor indicis (EI)?
distal insertion - extensor hood of index finger
action - extends the index finger
What is the distal insertion and action of extensor pollicis longus?
distal insertion - dorsal surface of base of distal phalanx of the thumb
action - extends the interphalangeal joint of the thumb
(can also extend carpometacarpal and metacarpophalangeal joints of thumb)
What is the distal insertion and action of extensor pollicis brevis (EPB)?
distal insertion - dorsal surface of base of proximal phalanx of thumb
action - extends metacarpophalangeal joint of thumb
(can also extend carpometacarpal joint of thumb)
What is the distal insertion and action of abductor pollicis longus (APL)?
distal insertion - lateral side of base of metacarpal I
action - abducts carpometacarpal joint of the thumb
acts as accessory extensor of thumb
What is the anatomical snuffbox and its boundaries?
it is a distinctive depression in the wrist between the tendons of:
- abductor pollicis longus
- extensor pollicis longus
- extensor pollicis brevis
What bone lies in the floor of the anatomical snuffbox?
the scaphoid bone
this is a carpal (wrist) bone
Which artery and vein can be palpated in the anatomical snuffbox?
the radial artery and cephalic vein
Label the components of the anatomical snuffbox
