Lecture 4: The forearm and wrist Flashcards
Where is the forearm?
The forearm houses the muscles which flex and extend the wrist, fingers and thumb. ‘Long’ tendons travel to the fingers and thumb > injury to the nerves which innervate the forearm muscles impair hand function
Where is the forearm?
The forearm houses the muscles which flex and extend the wrist, fingers and thumb. ‘Long’ tendons travel to the fingers and thumb > injury to the nerves which innervate the forearm muscles impair hand function
What is commonly fractured?
The distal radius
Is the ulna involved in the wrist?
No
What is the articulation in the wrist?
Articulation between the distal radius, scaphoid, and lunate
What type of joint is the Condyloid synovial joint?
Condyloid synovial joint (modified ball and socket)
Which ligaments strengthens the Condyloid synovial joint anteriorly and posteriorly?
Radiocarpal ligaments
Which side is the radius of the forearm?
Thumb side
What side is the Ulna of the forearm?
The medial side
What does the Ulna and radius bones articulate with?
Humerus at the elbow
How many bones does the radius articulate with at the wrist joint?
The radius articulates with 2 carpal bones at the radiocarpal (wrist) joint
Where does the ulna and radius articulate with each other?
Articulate with each other at the proximal and distal radioulnar joints (=pronation and supination
What connects the Ulna and the radius?
A strong interosseous membrane connects them. The IOM has holes in it for the passage of vessels
What can the wrist be referred to as?
Carpus
What does the carpus consist of?
= 8 small bones, arranged in 2 rows, that lie distal to the radius and ulna
What are the bones of the Hand?
Distal phalanges
Intermediate phalanges
Proximal phalanges
Metacarpals
Carpals
What are the joints of the hand?
Joints:
Distal interphalangeal (DIPJ)
Proximal interphalangeal (PIPJ)
Interphalangeal joint (IPJ) of the thumb
Metacarpophalangeal (MCPJ)
Carpometacarpal (CMCJ)
What muscles move the wrist?
Muscles in the forearm that cross the wrist = move the wrist
What else does the muscles in the forearm move?
The forearm also contains muscles that move the elbow, proximal radioulnar joint, thumb, and fingers
Where are the two muscle compartments in the forearm?
Anterior and Posterior
What do the muscles anteriorly in the forearm do?
Muscles in the anterior compartment flex (bend) the wrist (and digits)
What do the muscles posteriorly in the forearm do?
Muscles in the posterior compartment extend (straighten) the wrist (and digits)
What are the movements in the wrist?
Flexion and extension
Abduction and adduction
What are the movements in the wrist?
Flexion and extension
Abduction and adduction
How many layers of muscles are there in the anterior forearm?
3
What are most muscles in the anterior forearm innervated by?
Most are innervated by the median n. (C6-T1); a couple by the ulnar n. (C8-T1)
Insert on metacarpals or bones of the digits
General rules of the anterior forearm?
originate from the medial epicondyle of the humerus: the ‘common flexor origin’
flex either the wrist, thumb, or fingers
those that flex the thumb and fingers also contribute to flexion at the wrist
How many muscles pronate the forearm?
Two muscles pronate the forearm
The insertion points of tendons are key for clinical practice
How many muscle layers are there in the anterior superficial forearm?
4
What are the muscles in the anterior superficial layers of the forearm?
1 pronator = pronator teres
3 wrist flexors:
Flexor carpi radialis (flexor of the wrist, radial side)
Flexor carpi ulnaris (flexor of the wrist, ulnar side)
Palmaris longus
What are the muscles in the anterior superficial layer of the forearm innervated/ supplied by?
All supplied by the median n. except flexor carpi ulnaris (= ulnar nerve)
What lies withing the anterior middle layer of the forearm?
1 muscle with 4 tendons
= Flexor digitorum superficialis
Where does the anterior middle layer insert on?
Inserts on the middle phalanx of digits 2-5
What does the muscles in the anterior middle layer of the forearm do?
Flexes the fingers at the proximal interphalangeal joint
Because it crosses the wrist en-route to the fingers, it contributes to wrist flexion
How many muscles are in the anterior deep layer of the forearm?
3 muscles
What are the 3 muscles in the anterior deep layer of the forearm?
Flexor digitorum profundus
Flexor pollicis longus
Pronator quadratus
What does the flexor digitorum profundus do?
has 4 tendons = inserts on the distal phalanx > flexes the distal interphalangeal joint
What does the Flexor pollicis longus do
inserts on the distal phalanx > flexes the interphalangeal joint
Because these 2 cross the wrist, they can flex it
What does the Pronator quadratus do?
attachment to the distal radius and ulna > pronates the forearm
How many layers of muscles are in the posterior forearm?
2
One muscle supinates the forearm
One muscle abducts the thumb
What are the muscles of the posterior forearm innervated by?
All innervated by the radial n. (C5-T1)
Insert on the metacarpals or bones of the digits
What are the general rules for the posterior muscles of the forearm?
originate from the lateral epicondyle of the humerus: the ‘common extensor origin’
extend either the wrist, thumb or fingers
those that extend the thumb and fingers contribute to extension at the wrist,
How many muscles are in the posterior superficial layer of the forearm?
6
What are the muscles are in the posterior superficial layer of the forearm?
3 wrist extensors:
Extensor carpi radialis longus > 2nd MC
Extensor carpi radialis brevis > 3rd MC
Extensor carpi ulnaris > 5th MC
2 finger extensors:
Extensor digitorum = 4 tendons
Extensor digiti minimi = 1 tendon to little finger
What is the extensor expansion?
4 extensor tendons flatten to form extensor expansions/hoods
Triangular aponeurosis which wraps around dorsum and sides of fingers
What does the extensor expansion do?
Ensures extensor tendons stay within midline of finger
Where is the site of insertion for the extensor expansion?
Site of insertion for lumbricals and interossei muscles (next lecture)
How many muscles in the posterior deep layer of the forearm?
5
What are the muscles in the posterior deep layer of the forearm?
Supinator = of proximal RUJ
1 finger extensor:
Extensor indicis
2 thumb extensors:
Extensor pollicis longus > distal phalanx
Extensor pollicis brevis > proximal phalanx
1 thumb abductor
Abductor pollicis longus > 1st MC
What are the radial and ulnar arteries?
The radial and ulnar arteries are the terminal branches of the brachial. They course down the forearm to the wrist
What are the interosseous arteries?
The interosseous arteries are branches of the ulnar > supply the anterior and posterior forearm, respectively
Where do the median and ulnar nerves travel?
The median and ulnar nerves travel into the hand – only the median travels through the carpal tunne
Where do the deep and superficial branches of the radial nerves travel?
Down the forearm in the posterior compartment
What do deep veins in the forearm follow?
The arteries
What are the 2 major veins of the forearm?
cephalic and basilic – both drain the hand and important clinically for venepuncture / IV access
Where does the Cephalic vein form?
Anatomical snuffbox
Where does the basilic vein drain?
The basilic drains medial aspect of the dorsum of the hand
Where does the cephalic and basilic vein communicate?
Usually communicate in the cubital fossa via the median cubital vein
Superficial veins are variable!
What is Carpal tunnel syndrome?
Long flexor tendons and the median n. travel through the carpal tunnel
Median n. can be compressed by any condition that reduces space in the carpal tunnel
The skin and muscles that are innervated by median n. branches distal to the carpal tunnel are affected
What is the carpal tunnel?
The carpal tunnel = passageway in the wrist: the ‘floor’ is the arch of the carpus; roof is a fibrous sheet (flexor retinaculum)
What are the sensory symptoms of carpal tunnel syndrome?
Sensory symptoms (pain, pins and needles, tingling) in the areas of skin innervated by the median n.
Weakness in the hand muscles innervated by the median n. > the small muscles of the thumb
If not treated what are the consequences of carpal tunnel syndrome?
If CTS is not recognised and treated (by cutting ‘releasing’ the flexor retinaculum) permanent atrophy and weakness of the small thumb muscles results
