Cubital Fossa and Forearm Flexors

Objectives

• By the end of this lecture, students should be able to describe the cubital fossa (definition, boundaries, and contents).
• Students should be able to list the names of the Flexors Group of Forearm (superficial and deep muscles).
• Students should be able to identify the common flexor origin of flexor muscles and their innervation and movements.

Cubital Fossa

• Description: A triangular space in front of the elbow joint.

Cubital Fossa Boundaries

• Base: An imaginary line between the 2 epicondyles of the humerus.
• Lateral Boundary: Medial border of brachioradialis.
• Medial Boundary: Lateral border of pronator teres.
• Apex: Where the brachioradialis overlaps the pronator teres.

Cubital Fossa (Roof)

• Skin
• Superficial fascia contains the cephalic vein, lateral cutaneous nerve of the forearm, basilic vein, medial cutaneous nerve of the forearm and medial cubital vein.
• Deep fascia
• Bicipital aponeurosis

Cubital Fossa (Floor)

• Brachialis (medially)
• Supinator (laterally)

Cubital Fossa Contents (From lateral to medial)

• Radial nerve and its deep branch.
• Tendon of biceps brachii.
• Termination of the brachial artery and the beginning of the radial and ulnar arteries.
• Median nerve.

Components of the Anterior Compartment of the Forearm

• Muscles
• Nerves
• Vessels

Contents of the Anterior Compartment of the Forearm

• There are 8 muscles arranged in two groups: superficial (5) and deep (3)
• The vessels are the radial and ulnar.
• The nerves are the median and ulnar nerves, including the anterior interosseous branch of the median nerve.

Pronator Teres Muscle

• Origin: Two heads, humeral and ulnar.
• Insertion: Pronator tuberosity on the middle lateral surface of the radius.
• Nerve supply: Median nerve.
• Action: Pronation of the forearm and helps in flexion of the forearm.
• The lateral border forms the medial boundary of the cubital fossa.
• The median nerve passes between the two heads, and the ulnar artery passes deep to the ulnar head.

Flexor Carpi Radialis

• Origin: Medial epicondyle and adjoining deep fascia.
• Course: Forms a fusiform belly and a tendon in the middle of the forearm.
• Located at the wrist and accompanied by the tendon of the brachioradialis laterally.
• At this location the radial artery intervenes between two tendons.
• Insertion: Palmer surface of the base of the second and third metacarpal bones.
• Nerve Supply: Median nerve.
• Action: Flexion of the wrist and abduction of the wrist along with the ECRL (Extensor Carpi Radialis Longus) & ECRB (Extensor Carpi Radialis Brevis).

Palmaris Longus

• Origin: Medial epicondyle of the humerus.
• Course: Long tendon passing in front of the flexor retinaculum.
• Insertion: Continues as the central part of the palmar aponeurosis.
• Nerve Supply: Median nerve.
• Action: Weak flexor of the wrist.

Flexor Carpi Ulnaris

• Origin: Two heads, humeral head, which originates from the medial epicondyle of the humerus, and ulnar head, which originates from the medial margin of the olecranon process, and 2/3rd of the posterior border of the ulna.
• Course: The two heads form a tendinous arch, where the ulnar nerve and posterior ulnar recurrent artery passes below it.
• Insertion: Pisiform bone.
• Nerve Supply: Ulnar nerve.
• Action: Flexor of the wrist, along with ECU- Adduction.

Flexor Digitorum Superficialis

• Origin, 2 heads
• Humeroulnar:
  • Medial epicondyle of humerus
  • Medial margin of coronoid process
• Radial head:
  • Whole length of anterior oblique line of radius
• Course: Forms four tendons above the wrist, arranged in superficial (mostly radial) and deep groups of two each.
• Passes below the flexor retinaculum and diverges in the palm; superficial for the middle and ring fingers, and deep for the index and ring fingers
• Nerve supply: Median nerve.

Distal attachments of flexor digitorum superficialis (cont.):

• Insertion: At the base of the proximal phalanx, each digit tendon splits into two allowing for the passage of the tendon of F digitorum profundus
• The slips reunite again, and split again to be attached to the side of the shaft of the middle phalanx.
• Action: Flexion of the middle phalanx at the proximal interphalangeal joint.
• Action: Prolonged contraction leads to flexion of the metacarpophalangeal joint and the wrist joint

Deep Flexors

• Flexor Pollicis Longus
• Flexor Digitorum Profundus
• Pronator Quadratus

Flexor Pollicis Longus

• Origin: The anterior surface of the shaft of the radius below the anterior oblique line.
• Origin: Adjoining interosseous membrane.
• Course: Passes below the flexor retinaculum.
• Insertion: Palmar surface of the base of the distal phalanx of the thumb.
• Nerve Supply: Anterior interosseous branch of the median nerve.
• Action: Flexor of the thumb.

Flexor Digitorum Profundus

• Origin: Anterior and medial surface of the upper three-fourths of the shaft of the ulna, including the medial surface of coronoid and olecranon process.
• Origin: Adjoining interosseous membrane and the upper three-fourths of the posterior border of the ulna.
• Course: Forms four tendons.
• Course: Remains united except for the tendon for the index finger.
• Passes deep to the flexor retinaculum.
• Course: Diverges in the palm.
• Passes in between slips of superficialis.
• Course: Give origin to four lumbricals.
• Insertion: Palmar surface of the base of terminal (distal) phalanx of medial four fingers.
• Nerve Supply: Medial part- Ulnar nerve, Lateral part - Anterior Interosseous branch of median nerve
• Action: Flexes the terminal phalanx.

Pronator Quadratus

• Description: Quadrilateral muscle extends anteriorly in front of the interosseous membrane to both bones of the forearm.
• Origin: The bony ridge on the antero-medial surface of the lower 1/4th of the ulna.
• Insertion: The anterior surface of the lower 1/4th of the radius and adjoining anterior border of radius, triangular area just above the ulnar notch.
• Nerve Supply: Anterior interosseous branch of the median nerve.

Functional Classification of Flexor Muscles

• Flexors of the Wrist: FI. Carpi Radialis, FI. Carpi Ulnaris
• Flexors of Middle Phalanges: FI. Digitorum Superficialis
• Flexors of Distal Phalanges: FI. Digitorum Profundus, FI. Pollicis Longus
• Pronators of the Forearm: Pronator Teres, Pronator Quadratus

Ulnar Artery

• The larger of the two terminal branches of the brachial artery.
• Begins in the cubital fossa at the level of the neck of the radius.
• Descends through the anterior compartment of the forearm.
• Enters the palm in front of the flexor retinaculum with the ulnar nerve.
• Ends by forming the superficial palmar arch by anastomosing with the superficial palmar branch of the radial artery.

Ulnar Artery Branches

• Muscular branches.
• A recurrent branch for anastomosis around the elbow joint.
• A common interosseous artery, which gives anterior and posterior interosseous arteries.
• Branches to anastomoses around the wrist joint.

Radial Artery

• Smaller terminal branch of the brachial artery.
• Begins in the cubital fossa at the level of the neck of the radius.
• Descends downward and laterally.
• Leaves the forearm by winding around the lateral aspect of the wrist to reach the dorsum of the hand.

Radial Artery Branches

• Muscular
• Recurrent branch for anastomosis around the elbow joint.
• Superficial palmar branch, joins the ulnar artery to form the superficial palmar arch.

Nerve Supply

• All muscles on the front of the forearm are supplied by the median nerve except the flexor carpi ulnaris (FCU) and the medial half of the flexor digitorum profundus (FDP), which are supplied by the ulnar nerve.

Superficial Muscles

• The superficial group of muscles on the front of the forearm consists of five muscles arranged from lateral to medial:
  • Pronator teres
  • Flexor carpi radialis
  • Palmaris longus (15% are absent)
  • Flexor digitorum superficialis (lies in a deeper plane)
  • Flexor carpi ulnaris
• General Info:
  • Some have an additional origin from other bones.
  • The pronator teres is inserted in the radius, & the remaining 4 muscles are inserted in the hand.
  • All are supplied by the median nerve except the flexor carpi ulnaris supplied by the ulnar nerve.
  • All help in flexion of the elbow joint and have specific actions indicated by the name of the muscles.
• The nerve that innervates the flexor carpi radialis is the median nerve.