Unit 9 Forearm
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Where is the forearm?
The region of the upper limb between the elbow joint and the wrist joint.
What two compartments is the forearm divided into?
Posterior and Anterior compartments
What separates the compartments?
- A lateral intermuscular septum
- An interosseus membrane
- The attachment of deep fascia along the posterior border of the ulna
What is contained in the anterior compartment?
Contains muscles that predominately flex the wrist and digits and pronate the forearm
What is contained in the posterior forearm?
- Contains muscles that predominately extend the wrist and digits and supinate the forearm
- Major nerve and vessels supply or pass through each compartment
Describe the shaft of the radius
- Narrow proximally
- In cross-section it appears triangular with three borders and three surfaces
What are the three borders of the radius?
Describe the distal extremity of the radius
- Two facets for articulation with 2 carpal bones
- -Facet for articulation with scaphoid
- -Facet for articulation with lunate
Describe the shaft of the ulna
- The shaft of the ulna is broad superiorly where it is continuous with the large proximal end and narrow distally to form a small distal head.
- Like the radius, the shaft of the ulna is triangular in corss-section and has three borders and three surfaces
What are the borders of the ulna?
Describe the distal extremity of the ulna
The distal end of the ulna is small and characterized by a rounded head and the ulnar styloid process
Describe the head of the ulna
Covered by articular cartilage
Describe the styloid process
Originates from the dorsomedial aspect of the ulna and projects distally
What are the members of the Radio-ulnar joint?
- Head of the ulna
- Ulnar notch on the radius
- Fibrous articular disc
What is the Radio-ulnar joint classified as?
Modified ovoid joint
What is the function of the Radio-ulnar joint?
Allows the distal end of the radius to move anteriomedially over the ulna producing pronation and supination
Radius rotates at the elbow and distal end of the radius moves over the ulna
Describe the joint actions of the proximal radio-ulnar joint during pronation/supination
- Superior articular surface of the radius head spins on the capitulum
- The articular surface on the side of the head slides against the radial notch of the ulna
Describe the joint actions of the distal radio-ulnar joint during pronation/supination
The ulnar notch slides anteriorly over the convex surface of the head of the ulna
What holds the ulna and radius together during pronation/supination?
- Annular ligament of radius (PRUJ)
- Interosseous membrane
- the articular disc (DRUJ)
What are the muscles of the superficial layer of the anterior compartment?
- Pronator teres
- Flexor carpi radialis
- Palmaris longus
- Flexor carpi ulnaris
Name the muscle of the intermediate layer of the anterior compartment
Flexor digitorum superficialis
Name the muscles of the deep layer of the anterior compartment
- Flexor digitorum profundus
- Flexor pollicis longus
- Pronator quadratus
Name the muscles of the superifical layer of the posterior compartment
- Extensor carpi radialis longus
- Extensor carpi radialis brevis
- Extensor digitorum
- Extensor digiti minimi
- Extensor carpi ulnaris
What are the muscles of the deep layer of the posterior compartment?
- Abductor pollicis longus
- Extensor pollicis longus
- Extensor pollicis brevis
- Extensor indicis
Where does the radial artery originate?
From the brachial artery in the cubital fossa
Where does the radial artery pass?
- Passes along the lateral aspect of the forearm traveling:
- -Proximal 1/3 just deep to the brachioradialis muscle
- -Middle 1/3 with the superficial branch of the radial nerve
- -Distal 1/3 superficially covered only by deep fascia, superficial fascia, and skin
What does the radial artery supply?
Supplies the lateral forearm and forms the deep arch of the hand
Where can the radial artery pulse be taken?
Can be palpated in the distal forearm by moving lateral to the tendon of the FCR muscles
What are the proximal branches of the radial artery?
Radial recurrent artery
What are the main branches of the radial artery?
Superificial palmar branch
Where does the superficial palmar artery enter the hand?
Enters the hand by passing through or superficial to the thenar muscles at the base of the thumb
What does the superifical palmar branch anastomose with?
superificial palmar arch form by the ulnar artery
What is the function of the ulnar artery?
Supplies the medial forearm
Describe the course of the ulnar artery
- Leaves the cubital fossa by passing deep to the pronator teres muscle and then passes through the forearm in the fascial plane between FCU and FDP.
- In the distal forearm it remains tucked under the FCU tendion and is not easily palpable
What are the main branches of the ulnar artery?
- Anterior ulnar recurrent artery
- Posterior ulnar recurrent artery
- Common interosseous artery
What is the function of the anterior interosseous artery?
- Supplies muscles of the deep layer of the anterior forearm and the radius and ulna
- Contributes to the vascular network around the carpal bones
What is the function of the posterior interosseous artery?
Passes dorsally over the proximal margin of the interosseous membrane into the posterior compartment of the forearm
What is the innervation of the anterior compartment?
- Median Nerve - all muscles but 1 1/2
- Ulnar nerve - only 1 1/2 muscles
What is the innervation of the posterior compartment?
What does the Median N supply?
Supplies all of the muscles in the anterior compartment of the arm except for FCU/ulnar 1/2 FDP
Where does the Median nerve pass?
- Passes between the two head of the pronator teres muscle
- Travels in the forearm on the deep surface of the FDS
- Leaves the forearm and enters the palm by passing through the carpal tunnel deep to the flexor retinaculum
What are the two branches of the median nerve?
- Anterior interosseous nerve
- Palmar cutaneous nerve
Describe the anterior interosseous nerve and its innervation
- Originates between the 2 heads of the pronator teres
- Passes distally down the forearm with the anterior interosseous artery
- Innervates the muscles in the deep layer
- Terminates as articular branches to joints of the distal forearm and wrist
Describe the palmar cutaneous nerve and its innervation
- Oringinates in the distal forearm immediately proximal to the flexor retinaculum
- Innervates the skin over the base and central palm
Where does the ulnar nerve pass?
- Enters the anterior compartment by passing posteriorly around the medial epicondyle of the humerus and between the humeral and ulnar heads of the FCU.
- Travels in the medial side of the forearm in the plane between the FCU and FDP muscles.
- The ulnar artery is lateral to the ulnar nerve in the distal 2/3 of the forearm
How does the ulnar nerve enter the hand?
Superficial to the flexor retinaculum and lateral to the pisiform bone through Guyon's canal
What are the branches of the Ulnar nerve in the forearm?
- muscular branch to FCU and FDP
- Palmar cutaneous branch
- Dorsal cutaneous branch
What does the Palmar Cutaneous branch originate and what does it supply?
- Originates in the middle forearm
- Supplies the skin on the medial side of the palm
Where does the Dorsal Cutaneous Branch originate and what does it innervate?
- Originates in the distal forearm and passes posteriorly deep to the tendon of the FCU
- Innervates the skin on the dorsomedial side of the hand and most skin on the dorsal surface of the medial 1 1/2 digits
Where does the Deep Branch of the Radial n. pass and what does it innervate?
- Passes between the two heads of the supinator
- Predominately motor - innervates muscles of the superficial layer
Where does the Superficial branch of the Radial nerve pass and what does it innervate?
- Predominately cutaneous
- It passes down the anterolateral aspect of the dorearm deep to the brachioradialis muscle
- About 2/3 of the way down the fore the nerve becomes lateral and dorsal to the brachioradialis
Where does the Posterior Interosseous nerve from the Radial nerve pass and what does it innervate?
- Deep Radial n. becomes the posterior interosseous n. after emerging from between the two heads of the supinator muscle
- Supplies the muscles in the deep layer
- Terminates as articular branches which pass deep to the extensor pollicis longus muscle to reach the wrist
Name the three cuntaneous innervations of the forearm and where the stem from
- Lateral antebrachial cutaneous n. - musculocutaneous n.
- Medial antebrachial cutaneous n. - medial cord of the brachial plexus
- Posterior antebrachial cutaneous n. - radial n.
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