Anterior compartment of forearm

Question 1

Outline the anterior compartment of the forearm.

Answer 1

• The flexor muscles in the forearm are arranged in 2 groups, superficial and deep.
• The 5 muscles of the superficial group cross the elbow joint, the 3 muscles of the deep group do not.
• The flexor compartment is much more bulky than the extensor compartment, for the necessary power of the grip.
• These 5 muscles are distinguished by the fact that they possess a common origin from the medial epicondyle of the humerus.
• 3 of the group have additional areas of origin.
• The common origin is attached to a smooth area on the anterior surface of the medial epicondyle.
• With the heel of the hand placed over the opposite medial epicondyle, palm lying on the forearm, the digits point down along the 5 superficial muscles:
• Thumb for pronator teres
• Index finger for flexor carpi radialis
• Middle finger for flexor digitorum superficialis
• Ring finger for palmaris longus
• Little finger for flexor carpi ulnaris

Question 2

Pronator teres:
* Origin
* Insertion
* Nerve supply
* Action

Answer 2

• Origin - humeral head - common origin and lower part of medial supracondylar ridge. Ulnar head - medial side of the coronoid process of the ulna.
• Insertion - middle of the lateral surface of the radius.
• Nerve supply - the first (highest) muscular branch of the median nerve (C6, 7).
• Action - pronates the forearm and is a weak. flexor of the elbow.

Question 3

Flexor carpi radialis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 3

• Origin - common origin (medial epicondyle).
• Insertion - bases of the second and third metacarpal bones.
• Nerve supply - Median nerve (C6, 7).
• Action - flexor and radial abductor of the wrist.
  It is an important stabiliser of the wrist in finger and thumb movements.

Question 4

Flexor digitorum superficialis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 4

• Origin - humeroulnar head - common origin, medial ligament of elbow joint and medial border of the coronoid process of the ulna. Radial head - anterior oblique line of shaft of radius.
• Insertion - middle phalanges of the fingers.
• Nerve supply - median nerve (C7, 8).
• Action - flexor of the PIPJ and secondarily of the MCP and wrist joints.
  It also assists in flexion of the elbow and wrist.

Question 5

Palmaris longus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 5

• Origin - common origin.
• Insertion - palmar Aponeurosis and Flexor Retinaculum at the wrist joint.
• Nerve supply - median nerve (C7, 8).
• Action - Weak flexor of the wrist. Anchors skin and fascia of the hand against shearing forces in a distal direction.

Question 6

Flexor carpi ulnaris:
* Origin
* Insertion
* Nerve supply
* Action

Answer 6

• Origin - humeral head
• common origin. Ulnar head - olecranon and posterior border of the ulna.
• Insertion - base of pisiform bone, hook of hamate and base of 5th metacarpal.
• Nerve supply - ulnar nerve (C7, 8)
• Action - flexor and ulnar adductor of wrist.

Question 7

Describe the boundaries and contents of the cubital fossa.

Answer 7

• Triangular area between pronator teres, brachioradialis and a line joining the humeral epicondyles.
• Roof - formed by the deep fascia of the forearm, reinforced on the medial side by the bicipital aponeurosis.
• In front of the bicipital aponeurosis lies the median cubital vein with the medial cutaneous nerve of the forearm; the apnoneurosis separates these structures from the underlying median nerve and brachial artery.
• Floor - formed formed in the main by the brachialis muscle and below by the supinator.
• Contents of the fossa (from medial to lateral side) - median nerve, brachial artery, tendon of biceps and farther laterally the radial nerve and its posterior interosseous branch, which are only seen when brachioradialis is retracted laterally.
• The artery is palpated here medial to the tendon to define the position for placing the stethoscope when taking the blood pressure.
• The posterior interosseous nerve gives branches to extensor carpi radialis brevis and supinator before disappearing from the fossa by passing between the 2 layers of the supinator muscle into the extensor compartment.
• The superficial branch of the radial nerve passes down the forearm under cover of the brachioradialis.

Question 8

What are the 3 deep muscles of the anterior compartment of forearm?

Answer 8

• Flexor digitorum profundus
• Flexor pollicis longus
• Pronator quadratus

Question 9

Flexor digitorum profundus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 9

• Origin - medial surface of the olecranon, from the upper 2/3rds of the anterior and medial surfaces of the ulna and from the interosseous membrane.
• Insertion - palmar surface of the base of the distal phalanx of digits 2nd to 5th.
• Nerve supply - medial half (associated with ring and little fingers) is innervated by ulnar nerve. Lateral half (associated with middle and index fingers) by anterior interosseous nerve (C8, T1) - motor branch of median nerve.
• Action - the chief gripping muscle. lt acts best when the wrist is extended. It is the sole flexors of DIPJ of digit 2nd to 5th. It also acts as a flexor of the wrist (midcarpal), MCPJ and PIPJ of the index, middle, ring, and little fingers along with flexor digitorum superficialis.

Question 10

Flexor pollicis longus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 10

• Origin - mid half of the anterior surface of the radius and adjacent half of the interosseous membrane.
• Insertion - base of distal phalanx of thumb.
• Nerve supply - anterior interosseus branch of the median nerve (C7, 8).
• Action - only flexor of the interphalangeal joint of the thumb, and carpometacarpal joints of the thumb and the wrist joint.

Question 11

Pronator quadratus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 11

• Origin - oblique ridge on the anterior surface of the distal fourth of the ulna.
• Insertion - lateral border and anterior surface of the distal fourth of the radius.
• Nerve supply - anterior interosseous branch of the median nerve (C7, 8).
• Action - contraction of this muscle pulls the distal end of the radius over the ulna, resulting in the pronation of the radioulnar joint. As a pronator, it is more powerful than pronator teres.

Question 12

Outline the radioulnar joints.

Answer 12

• The superior radioulnar joint is a uniaxial synovial pivot joint between the circumference of the head of the radius and the fibro-osseous ring formed by the annular ligament and the radial notch of the ulnar.
• The articular inner aspect of the annular ligament is lined by hyaline cartilage.
• The capsule and lateral ligament of the elbow joint are attached to the annular ligament and both joints share the same synovial membrane.
• The membrane lines the intracapsular part of the radial neck and is supported below by the quadrate ligament.
• The inferior radioulnar joint is a uniaxial synovial pivot joint between the convex head of the ulnar and the concave ulnar notch of the radius.
• A triangular, fibrocartilaginous articular disc is attached by its base to the lower margin of the ulnar notch of the radius and by its apex to a fossa at the base of the ulnar styloid.
• The proximal surface of the disc articulates with the ulnar head.
• The synovial membrane of the joint projects proximally, as the recessus sacciformis, posterior to the pronator quadratus and anterior to the interosseous membrane.