Posterior forearm and upper limb joints

Question 1

What are the extensors?

Answer 1

The muscles in the posterior forearm are generally known as the extensors as they produce extension at the wrist and fingers. They are all innervated by the radial nerve. They are split into the superficial and deep layers.

Question 2

What are the major features of the brachioradialis?

Answer 2

PARADOXICAL - origin and insertion match the extensors, but acts as a flexor.
Superficial
Originates from lateral supracondylar ridge of the humerus.
Attaches at the distal end of the radius.
Acts to flex at the elbow.
Innervated by the radial nerve

Question 3

What are the major features of the Extensor Carpi radialis longus and brevis?

Answer 3

Superficial extensors
ECRL originates from the supracondylar ridge.
ECRB originates from the lateral epicondyle.
Attaches to metacarpal bones II and III.
Act to extend and abduct the wrist.
Innervated by the radial nerve.

Question 4

What are the major features of the Extensor digitorum?

Answer 4

Superficial
Main extensor of the fingers.
Originates from the lateral epicondyle.
Attaches to the extensor hood of each finger.
Acts to extend medial 4 fingers at the metacarpal and interphalangeal joints.
Innervated by the radial nerve.

Question 5

What are the extensor hoods?

Answer 5

The extensor digitorum gives rise to four tendons which insert into digits 2-5.
Each slip forms an expanded hood over the dorsum of the digit.
The expansion is attached to the base of the proximal phalanx before dividing into a central and two marginal slips.
The central slip is inserted onto the base of the middle phalanx. The marginal slips unite together and insert onto the base of the distal phalanx. The interossei and the lumbricals are inserted on the proximal part of the extensor expansion.

Question 6

What are the major features of the extensor digiti minimi?

Answer 6

Superficial extensor
Sometimes fused with the extensor digitorum.
Originates from the lateral epicondyle.
Attaches to the extensor hood of the little finger with the extensor digitorum tendon.
Acts to extend the little finger and contributes to extension at the wrist.
Innervated by the radial nerve.

Question 7

What are the major features of the extensor carpi ulnaris?

Answer 7

Superficial extensor
Originates from the lateral epicondyle of the humerus.
Attaches to the base of metacarpal V.
Acts to extend and adduct the wrist.
Innervated by the radial nerve.

Question 8

What are the major features of the aconeus?

Answer 8

Superficial
Can be blended with the fibres of the triceps brachii.
Originates from the lateral epicondyle of the humerus.
Attaches onto the olecranon of the ulna.
Acts to extend and stabilise the elbow joint, abducts the ulna during pronation of the forearm.
Innervated by the radial nerve.

Question 9

What are the major features of the supinator?

Answer 9

Deep
Lies in the floor of the cubital fossa.
It has two heads that the deep branch of the radial nerve passes through.
One head originates from the lateral epicondyle of the humerus, the other originates from the posterior surface of the ulna.
Insert onto the posterior surface of the radius.
Acts to supinate the forearm.
Innervated by the radial nerve.

Question 10

What are the major features of the Abductor pollicis longus?

Answer 10

Deep
Its tendon contributes to the lateral border of the anatomical snuffbox.
Originates from the interosseous membrane and posterior surfaces of the radius and ulna.
Attaches to the lateral side of metacarpal I.
Acts to abduct the thumb.
Innervated by the radial nerve.

Question 11

What are the major features of the Extensor pollicis brevis?

Answer 11

Deep
Its tendon contributes to the lateral border of the anatomical snuffbox.
Originates from the posterior radius and interosseous membrane.
Attaches to the base of the proximal phalanx of the thumb.
Acts to extend the thumb at the metacarpal and interphalangeal joints.
Innervated by the radial nerve.

Question 12

What are the major features of the Extensor pollicis longus?

Answer 12

Deep
Larger muscle belly than the extensor pollicis brevis.
Its tendon forms the medial border of the anatomical snuffbox.
Originates from the posterior surface of the ulna and interosseous membrane.
Attaches to the distal phalanx of the thumb.
Acts to extend all joints of the thumb: carpometacarpal, metacarpophalangeal and interphalangeal.
Innervated by the radial nerve.

Question 13

What are the major features of the Extensor Indicis Proprius?

Answer 13

Allows the index finger to be independent of the other fingers during extension.
Originates from the posterior surface of the ulna and interosseous membrane.
Attaches to the extensor hood of the index finger.
Acts to extend the index finger.
Innervated by the radial nerve.

Question 14

What is the anatomical snuffbox?

Answer 14

A space proximal to the thumb bounded medially by the extensor pollicis longus and laterally by the tendons of the abductor pollicis longus and the extensor pollicis brevis.
The scaphoid bone forms its floor.
The radial artery lies in it and the cephalic vein crosses it superficially.

Question 15

What is tennis elbow?

Answer 15

Damage to the common extensor origin (lateral epicondyle of the humerus) causes pain here.

Question 16

What is golfer’s elbow?

Answer 16

Damage to the common flexor origin (medial epicondyle of the humerus) causes pain here.

Question 17

What is Mallet’s finger?

Answer 17

Acute injury
Rupture of the insertion of the extensor tendon into the distal phalanx. Interphalangeal joint is held in flexion but can return to extension by being moved manually.

Question 18

What is Swan neck finger?

Answer 18

Chronic injury
Rupture of the insertion of the extensor tendon into the distal phalanx. Interphalangeal joint is held in flexion. The extensor tendon still attached to the middle phalanx will try and compensate by pulling harder and eventually the proximal interphalangeal joint will be held in extension.

Question 19

What is a Boutonniere deformity?

Answer 19

If the insertion of the extensor tendon onto the middle phalanx ruptures then the proximal interphalangeal joint will be held in flexion. The extensor tendon, which is still attached to the distal phalanx, will try and compensate by pulling harder and eventually the distal interphalangeal joint is held in extension. The proximal interphalangeal joint pokes through the gap in the extensor tendon a bit like a button, hence the name.

Question 20

How does the elbow flex and extend?

Answer 20

Flexion and extension movements of the forearm take place at the elbow joint.
The anterior compartment of the arm contains the flexor muscles (brachialis, biceps and brachioradialis) and the posterior compartment of the arm contains the extensor group (triceps).

Question 21

How does supination and pronation occur at the elbow?

Answer 21

At the superior radio-ulnar joint the radius is able to rotate to produce pronation and supination.
Pronation is produced by pronator teres and pronator quadratus.
Supination is weak when the elbow is in full extension and is produced by the supinator muscle. When the elbow is flexed to 90 degrees, biceps acts as a very powerful supinator.

Question 22

Why is radius able to rotate freely?

Answer 22

In the elbow joint, the upper surface of the head of radius articulates with the capitulum of the humerus and the trochlea of the humerus fits into the trochlear notch of the ulna.
The upper end of the radius is totally free of ligamentous attachments enabling the radius to rotate freely inside the annular ligament.

Question 23

Which bones articulate at the wrist joint?

Answer 23

At the wrist joint, the scaphoid, lunate and the triquetral bones articulate proximally with the distal end of the radius and the triangular fibrocartilage connecting the distal end of the radius and the ulna. The triangular fibrocartilage separates the wrist joint from the inferior radioulnar joint.