S8) The Forearm Flashcards
Describe the structure, location and function of the ulna
- Structure: long bone in the forearm
- Location: lies medially, parallel to the radius
- Function: stabilising bone, pivots with the radius to produce movement
Describe the articulations of the ulna
- Proximal: articulates with trochlea of humerus at the elbow joint and head of the radius at proximal radio-ulnar joint
- Distal: radius at the distal radio-ulnar joint
Identify the important anatomical landmarks in the proximal region of the ulna
Describe the structure and purpose of the olecranon, ulna tuberosity and coronoid process
- Olecranon – a large projection of bone that extends proximally, forming part of trochlear notch
- Coronoid process – a ridge of bone projecting outwards anteriorly, forming part of the trochlear notch
- Tuberosity of ulna – a roughening immediately distal to the coronoid process
Describe the structure and purpose of the trochlear and radial notch
- Trochlear notch is formed by the olecranon and coronoid process and articulates with the trochlea of the humerus
- Radial notch is located on the lateral surface of the trochlear notch and articulates with the head of the radius
Describe the structure of shaft of the ulna
The ulnar shaft is triangular, with three borders and three surfaces and decreases in width distally
The shaft of the ulna has three surfaces.
Identify and describe them
- Anterior – site of attachment for the pronator quadratus muscle distally
- Posterior – site of attachment for many muscles
- Medial – unremarkable
The shaft of the radius has three borders.
Identify and describe them
- Posterior – palpable along the entire length of the forearm posteriorly
- Interosseous – site of attachment for the interosseous membrane
- Anterior – unremarkable
Identify the important anatomical landmarks in the distal region of the ulna
Describe the structure, location and function of the radius
- Structure: long bone in the forearm
- Location: lies laterally, parallel to ulna
- Function: pivots around the ulna to produce movement at the radio-ulnar joints
The radius articulates in four places.
Identify and describe them
- Elbow Joint – articulation between radial head and capitulum of humerus
- Proximal Radioulnar Joint – articulation between the radial head and radial notch of the ulna
- Distal Radioulnar Joint – articulation between ulnar notch of radius and ulnar head
- Wrist Joint – articulation between the distal radius and carpal bones
Identify the important anatomical landmarks in the proximal region of the radius
Describe the structure of the radial head, neck and radial tuberosity.
- Head of radius – disk shaped structure with a concave articulating surface and forms the proximal radioulnar joint
- Neck – narrow area of bone, which lies between the radial head and radial tuberosity
- Radial tuberosity – a bony projection
What holds the radial head in place during movement?
- The radial head is held in place by the annular radial ligament, which forms a collar around the joint
- The is lined with a synovial membrane, reducing friction during movement
Describe the structure of the shaft of the radius
- It is triangular in shape, with three borders and three surfaces and expands in diameter distally
- The lateral surface has a small roughening for the attachment of the pronator teres muscle
Identify the important anatomical landmarks in the distal region of the radius
Describe the structure and purpose of the styloid process, ulnar notch and scaphoid and lunate facets
- Styloid process – distal projection of lateral side of radial shaft
- Ulnar notch – concavity on medial surface which articulates with the head of ulna, forming the distal radioulnar joint
- Scaphoid and lunate facets – articulate with the scaphoid and lunate carpal bones to form the wrist joint
The radioulnar joints are two locations in which the radius and ulna articulate in the forearm.
Describe their anatomical position and articulation
- Proximal radioulnar joint is an articulation between the head of the radius, and the radial notch of the ulna (located near the elbow)
- Distal radioulnar joint is an articulation between the head of the ulna and the ulnar notch of the radius (located proximal to wrist joint)
What type of joint are the radioulnar joints?
The radioulnar joint is a pivot type synovial joint
Identify the movements possible at the radioulnar joints and the muscles responsible
- Pronation produced by the pronator quadratus and pronator teres
- Supination produced by the supinator and biceps brachii
The articular disk is a fibrocartilaginous ligament present in the distal radioulnar joint.
What are its functions?
- Binds the radius and ulna together, and holds them together during movement at the joint
- Separates the distal radioulnar joint from the wrist joint
What are three major functions of the interosseous membrane?
- Holds the radius and ulna together during pronation and supination
- Acts as a site of attachment for muscles of the forearm
- Transfers forces from the radius to the ulna
Identify the 3 types of muscles in the anterior compartment of the forearm
- Superficial muscles
- Intermediate muscles
- Deep muscles
Identify the superficial muscles in the anterior compartment of the forearm
- Flexor carpi ulnaris
- Flexor carpi radialis
- Palmaris longus
- Pronator teres
What is a common characteristic of all superficial muscles in the anterior compartment of the forearm?
They all originate from a common flexor tendon, which arises from the medial epicondyle of the humerus
State the function and innervation of the flexor carpi ulnaris muscle
- Function: wrist flexion and adduction
- Innervation: ulnar nerve
State the origin and attachment of the flexor carpi ulnaris muscle
- Origin: medial epicondyle
- Attachment: pisiform carpal bone
State the function and innervation of the palmaris longus muscle
- Function: wrist flexion
- Innervation: median nerve
State the origin and attachment of the palmaris longus muscle
- Origin: medial epicondyle
- Attachment: flexor retinaculum of the wrist
State the function and innervation of the flexor carpi radialis muscle
- Function: wrist flexion and abduction
- Innervation: median nerve
State the origin and attachment of the flexor carpi radialis muscle
- Origin: medial epicondyle
- Attachment: base of metacarpals II and III
State the function and innervation of the pronator teres muscle
- Function: pronation of the forearm
- Innervation: median nerve
State the origin and attachment of the pronator teres muscle
- Origin: medial epicondyle and coronoid process of the ulna
- Attachment: laterally on mid-shaft of the radius
Which muscle is in the intermediate compartment of the anterior forearm?
Flexor digitorum superficialis
Why is the flexor digitorum superficialis a good anatomical landmark in the forearm?
The median nerve and ulnar artery pass between its two heads, and then travel posteriorly
State the function and innervation of the flexor digitorum superficialis muscle
- Function: MCPJ flexion, PIPJ flexion (4 fingers), wrist flexion
- Innervation: median nerve
State the origin and attachment of the flexor digitorum superficialis muscle
- Origin:
I. One head – medial epicondyle of the humerus
II. Other head – radius
- Attachment: four tendons travel through the carpal tunnel and attach to the middle phalanges of the four fingers
Identify the deep muscles in the anterior compartment of the forearm
- Flexor digitorum profundus
- Flexor pollicis longus
- Pronator quadratus
State the function and innervation of the flexor digitorum profundus muscle
- Function: DIPJ flexion (only muscle), MCPJ flexion
- Innervation:
I. Ulnar nerve – medial half
II. Median nerve – lateral half
State the origin and attachment of the flexor digitorum profundus muscle
- Origin: ulna and associated interosseous membrane
- Attachment: splits into four tendons, passes through the carpal tunnel and attaches to distal phalanges of four fingers
State the function and innervation of the flexor pollicis longus muscle
- Function: IPJ flexion, MCPJ flexion
- Innervation: median nerve
State the origin and attachment of the flexor pollicus longus muscle
- Origin: anterior surface of the radius and surrounding interosseous membrane
- Attachment: base of the distal phalanx of the thumb
State the function and innervation of the pronator quadratus muscle
- Function: pronates the forearm
- Innervation: median nerve
State the origin and attachment of the pronator quadratus
- Origin: anterior surface of the ulna
- Attachment: anterior surface of the radius
Describe the general structure, function and innervation of the extensor muscles of the posterior forearm
- Structure: superficial and deep layers (separated by a layer of fascia)
- Function: produce extension at the wrist and fingers
- Innervation: radial nerve
Identify the superficial muscles in the posterior compartment of the forearm
- Brachioradialis
- Extensor carpi radialis longus
- Extensor carpi radialis brevis
- Extensor digitorum
- Extensor digiti minimi
- Extensor carpi ulnaris
- Anconeus
What is a common characteristic of the extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum and extensor digiti minimi muscles?
They all originate from the same extensor tendon, which arises at the lateral epicondyle of the humerus
State the function and innervation of the brachioradialis
- Function: elbow flexion
- Innervation: radial nerve
State the origin and attachments of the bracioradialis muscle
- Origin: proximal aspect of the lateral supracondylar ridge of humerus
- Attachment: distal end of the radius (before the radial styloid process)
State the function and innervation of the extensor carpi radialis muscles
- Function: wrist extension, wrist abduction
- Innervation: radial nerve
State the origin and attachments of the extensor carpi radialis muscles
- Origin:
I. ECRL – supracondylar ridge
II. ECRB – lateral epicondyle
- Attachment: metacarpal bones II and III
State the function and innervation of the extensor digitorum muscle
- Function: finger extension at the MCPJs and IPJs (not thumb)
- Innervation: radial nerve
State the origin and attachment of the extensor digitorum muscle
- Origin: lateral epicondyle
- Attachment: extensor hood of each finger
State the function and innervation of the extensor digiti minimi muscle
- Function: little finger extension, contributes to wrist extension
- Innervation: radial nerve
State the origin and attachment of the extensor digiti minimi muscle
- Origin: lateral epicondyle of the humerus
- Attachment: extensor hood of the little finger (with extensor digitorum tendon)
State the function and innervation of the extensor carpi ulnaris muscle
- Function: wrist extension, wrist adduction
- Innervation: radial nerve
State the origin and attachment of extensor carpi ulnaris
- Origin: lateral epicondyle of the humerus
- Attachment: base of metacarpal V
Describe the structure, function and innervation of the anconeus muscle
- Structure: blended with the fibres of the triceps brachii (two muscles can be indistinguishable)
- Function: extends and stablises the elbow joint
- Innervation: radial nerve
State the origin and attachment of the anconeus muscle
- Origin: lateral epicondyle
- Attachment: posterior and lateral part of the olecranon
Identify the deep muscles of the posterior compartment of the forearm
- Supinator
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus
- Extensor indicis
Describe the structure, function and innervation of the supinator muscle
- Structure: floor of the cubital fossa, two heads – deep branch of the radial nerve passes between
- Function: supination
- Innervation: radial nerve
State the origin and attachment of the supinator muscle
- Origin:
I. One head – lateral epicondyle of the humerus
II. Other head – posterior surface of the ulna
- Attachment: posterior surface of the radius
Describe the structure, function and innervation of the abductor pollicis longus muscle
- Structure: tendon contributes to lateral border of anatomical snuffbox
- Function: thumb abduction
- Innervation: radial nerve
State the origin and attachment of the abductor pollicis longus muscle
- Origin: interosseous membrane and adjacent posterior surfaces of the radius and ulna
- Attachment: lateral side of the base of metacarpal I
Describe the structure, function and innervation of the extensor pollicis brevis muscle
- Structure: tendon contributes to lateral border of anatomical snuffbox
- Function: thumb extension at the MCPJs and CMCJs
- Innervation: radial nerve
State the origin and attachment of the extensor pollicis brevis muscle
- Origin: posterior surface of the radius and interosseous membrane
- Attachment: base of the proximal phalanx of the thumb
Describe the structure, function and innervation of the extensor pollicis longus muscle
- Structure: tendon forms medial border of anatomical snuffbox
- Function: thumb extension at CMCJs, MCPJs, IPJs
- Innervation: radial nerve
State the origin and attachment of the extensor pollicus longus muscle
- Origin: posterior surface of the ulna and interosseous membrane
- Attachment: distal phalanx of the thumb
State the function and innervation of the extensor indicis proprius
- Function: index finger extension (independent)
- Innervation: radial nerve
State the origin and attachment of the extensor indicis proprius
- Origin: posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus
- Attachment: extensor hood of the index finger
Identify the nerves of the forearm
Describe the arterial supply of the forearm
- Radial artery supplies the posterior aspect of the forearm
- Ulnar artery supplies the anterior aspect of the forearm
The two arteries anastomose in the hand, by forming two arches, the superficial palmar arch, and the deep palmar arch
Identify the veins of the forearm
What is a Colles’ fracture?
A Colles’ fracture is a distal radius fracture caused by a direct blow to the palmar forearm or falling onto extended wrists leading to dorsal displacement
What is a Smith’s fracture?
A Smith’s fracture is a distal radius fracture caused by a direct blow to the dorsal forearm or falling onto flexed wrists leading to palmar displacement
