Posterior forearm

Question 1

What are muscles in the posterior forearm commonly known as?

Answer 1

The extensor muscles

Question 2

What is the general function of the extensor muscles?

Answer 2

Tp produce extension at the wrist and fingers.

Question 3

What nerve innervates the extensor muscles?

Answer 3

Radial nerve

Question 4

Brachioradialis (attachments, actions, innervation)

Answer 4

Paradoxical muscles as its origin and innervation are characteristic of extensor muscles but, it is actually a flexor at the elbow.

Attachments: Origionates from the proximal aspect of the lateral supracondylar ridge of the humerus and attatches to the distal end of the radius, just before the styloid process.

Actions: Flexes at the elbow

Innervation: Radial nerve

Question 5

Extensor Carpi Radialis Longus and Brevis (attachments, actions, innervation)

Answer 5

Situated on the lateral aspect of the posterior forearm.

Attachments: The ECRL origionates from the supracondylar ridge while the ECRB origionates from the lateral epicondyle. Their tendon attatch to the metacarpal bones II and III.

Actions: Extends and abducts the wrist

Innervation: Radial nerve

Question 6

Extensor Digitorum (attachments, actions, innervation)

Answer 6

This is the main extensor of the fingers. To test the function of the muscle, the forearm is pronated and the fingers extended against resistance.

Attachments: Originates from the lateral epicondyle. The tedon continues into in the distal part of thr forearm, where is splits into fourm and inserts nto the extensor hood of each finger.

Actions: Extends medial four fingers at the MCP and IP joints.

Innervations: Radial nerve (deep branch)

Question 7

Extensor Digiti Minimi (Attachments, Actions, Innervation)

Answer 7

Origionates from the extensor digitorum muscle. In some people, there two muscles are fused together. Anatomically, the extensor digiti minimi lies medially to te extenor digitorum.

Attachments: Originates form the lateral epicondyle of the humerus. It attaches with the extensor digitorum tendon into the hood of the little finger.

Actions: Extends the little finger and contributes to extension at the wrist.

Innervation: Radial nerve (deep branch)

Question 8

Extensor Carpi Ulnaris (Attachments, Actions, Innervation)

Answer 8

It is located on the medial aspect of the posterior forearm.

Attachments: Origionates from the lateral epicondyle of the humerus and attaches to the base of metacarpal V.

Actions: Extension and adduction of wrist (due to its position)

Innervation: Radial Nerve (deep branch)

Question 9

Acroneus (Attachments, Actions, Innervation)

Answer 9

Situated medially and superiorly in the extensor campartment of the forearm. It is blended with fibres of the triceps brachii and the two muscles can be indistinguishable.

Attachments: Originates from the lateral epicondyle and attaches to the posterior and lateral part of the olecranon.

Actions: Extends and stabilises the elbow joint. Abducts the ulna during pronation of the forearm.

Innervation: Radial nerve.

Question 10

What is Lateral Epicondylitis?

Answer 10

Lateral epicondylitis (or tennis elbow) refers to inflammation of the periosteum of the lateral epicondyle.

The peak age of onset is 40-50yrs old

It is caused by repeated use of the superficial extensor muscles, which strains their commont tendinous attatchment to the lateral epicondyle.

Question 11

What are the deep muscles of the posterior forearm?

Answer 11

There are five muscles in the deep compartment of the posterior forearm:

• Supinator
• Abductor pollicis
• Pollicis longus
• Extensor pollicis brevis
• Extensor pollicis longus
• Extendor indicis

With the exception of supinator, there muscles act on the thumb and index finger.

Question 12

Supinator (Attachments, Actions, Innervation)

Answer 12

Supinator lies in the floor of the cubital fossa. It has two heads, which the deep branch of the radial nerve passes between.

Attchments: It has two heads of origin. One origionates from the lateral epicondyle of the humerus, the other from the posterior surface of the ulna. They insert together into the posterior surface of the radius.

Actions: Supinates the forearm

Innervation: Radial nerve (deep branch)

Question 13

Abductor Pollicis Longus (Attachments, Actions, Innervation)

Answer 13

It is situated immediately distal to the supinator muscle. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox.

Attachments: Origionates from the interosseous membrane and the adjacent posterior surfaces of the radius and the ulna. It attaches to the lateral side of the base of metacarpal I.

Actions: Abducts the thunb.

Innervation: Radial neve (Posterior interossous branch)

Question 14

Extensor Pollicis Brevis (Attachments, Actions, Innervation)

Answer 14

Located medially deep to the abductor pollicis longus. Lateral border to the anatomical snuffbox.

Attachments: Origionates from the posterior surface of the radius and interosseous membrane. It attaches to the base of the proximal phalanx of the thumb.

Actions: Extends at the metacarpophalangeal and carcometacarpal joints of the thumb.

Innervation: Radial nerve (Interosseous branch)

Question 15

Extensor Pollicis Longus (Attachments, Actions, Innervation)

Answer 15

• EPL has a large muscle belly than EPB.
• Its tendon travels medially to the dorsal tubercle at the wrist, using the tubercle as a pulley to increase the force exerted.
• The tendon of the extensor pollicis longus forms the medial border of the anatomical snuffbox in the hand.

Attachments: Originates from thhe posterior surface of the ulma and interosseous membrane. It attaches to the stal phalanx of the thumb.

Actions: Extends all joints of the thumb: carpomeracarpal, metacarpophalangeal and interphalangeal.

Innervation: Radial nerve (posterior interosseous branch)

Question 16

Extensor Indicis Proprius

Answer 16

This muscle allows the index finger to be independant of the other fingers during extension.

Attachments: Origionates from the posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus. Attaches to the extensor hood of the index finger.

Actions: Extends the index finger.

Innervation: Radial nerve (posterior interosseous branch)

Question 17

What is a wrist drop?

Answer 17

Wrist drop is a sign of radial injury that has occured proximal to the elbow.

There are two common characteristics sites of damage:

• Axilla - injured via humeral dislocations or fractures of the proximal humerus
• Radial groove of the humerus - injured via a humeral shaft fracture.

Radial nerve innervates all muscles in the extensor compartment of the forearm. In the event of a radial merve lesion, these muscles are paralysed. The muscles that flex the wrist are innervated by the median nerve and are thus unaffected. The tone of the flexor muscles produces upopposed flexion at the wrist joint - wrist drop.