Muscles Acting on the Fingers, Blood Supply, and Innervation.

Muscles Acting on the Fingers, Blood Supply, and Innervation

The fingers are highly specialized for a wide range of functions, including grasping, pinching, and performing delicate tasks. The muscles responsible for these movements are located in the forearm and the hand, while the blood supply and innervation are provided by major arteries and nerves in the upper limb. A thorough understanding of the muscles, blood supply, and innervation is essential for understanding the complex motor and sensory capabilities of the fingers.

Muscles Acting on the Fingers

1. Flexor Muscles of the Fingers

These muscles are primarily located in the anterior compartment of the forearm. They act to flex the fingers and are essential for grip strength and precision.

• Flexor Digitorum Superficialis (FDS):

  • Origin: Medial epicondyle of the humerus, coronoid process of the ulna, and the radius.

  • Insertion: Middle phalanges of the 2nd to 5th fingers.

  • Action: Flexes the proximal interphalangeal joints (PIP) and assists in flexing the metacarpophalangeal joints (MCP).

  • Innervation: Median nerve (C7, C8, T1).

• Flexor Digitorum Profundus (FDP):

  • Origin: Proximal 3/4 of the anterior and medial surfaces of the ulna and the interosseous membrane.

  • Insertion: Distal phalanges of the 2nd to 5th fingers.

  • Action: Flexes the distal interphalangeal joints (DIP) and assists in flexing the MCP and PIP joints.

  • Innervation: Median nerve (C8, T1) for the 2nd and 3rd fingers, Ulnar nerve (C8, T1) for the 4th and 5th fingers.

• Flexor Pollicis Longus (FPL):

  • Origin: Anterior surface of the radius and interosseous membrane.

  • Insertion: Distal phalanx of the thumb.

  • Action: Flexes the thumb and assists in flexing the wrist.

  • Innervation: Median nerve (C8, T1).

2. Extensor Muscles of the Fingers

These muscles are located in the posterior compartment of the forearm and act to extend the fingers, facilitating release movements and opposing grasping.

• Extensor Digitorum (ED):

  • Origin: Lateral epicondyle of the humerus.

  • Insertion: Extensor expansions of the 2nd to 5th fingers.

  • Action: Extends the MCP, PIP, and DIP joints of the fingers.

  • Innervation: Radial nerve (C7, C8).

• Extensor Indicis (EI):

  • Origin: Posterior surface of the ulna and interosseous membrane.

  • Insertion: Extensor expansion of the index finger.

  • Action: Extends the index finger and assists in wrist extension.

  • Innervation: Radial nerve (C7, C8).

• Extensor Digiti Minimi (EDM):

  • Origin: Lateral epicondyle of the humerus.

  • Insertion: Extensor expansion of the 5th finger.

  • Action: Extends the little finger and assists in wrist extension.

  • Innervation: Radial nerve (C7, C8).

• Abductor Pollicis Longus (APL):

  • Origin: Posterior surface of the radius and ulna and interosseous membrane.

  • Insertion: Base of the 1st metacarpal.

  • Action: Abducts and extends the thumb.

  • Innervation: Radial nerve (C7, C8).

• Extensor Pollicis Longus (EPL):

  • Origin: Posterior surface of the ulna and interosseous membrane.

  • Insertion: Distal phalanx of the thumb.

  • Action: Extends the thumb at the IP joint, and assists in wrist extension.

  • Innervation: Radial nerve (C7, C8).

• Extensor Pollicis Brevis (EPB):

  • Origin: Posterior surface of the radius and interosseous membrane.

  • Insertion: Proximal phalanx of the thumb.

  • Action: Extends the thumb at the MCP joint.

  • Innervation: Radial nerve (C7, C8).

3. Intrinsic Muscles of the Hand

These muscles are located in the palmar region of the hand and contribute to fine motor movements of the fingers.

• Lumbricals:

  • Origin: Tendons of the flexor digitorum profundus.

  • Insertion: Extensor expansions of the 2nd to 5th fingers.

  • Action: Flex the MCP joints and extend the PIP and DIP joints.

  • Innervation: Median nerve (lateral two lumbricals), Ulnar nerve (medial two lumbricals).

• Interossei Muscles:

  • Palmar Interossei (PAD):

    • Origin: Sides of the metacarpals.

    • Insertion: Base of the proximal phalanges and extensor expansions of the 2nd, 4th, and 5th fingers.

    • Action: Adduct the fingers toward the midline of the hand.

    • Innervation: Ulnar nerve (deep branch).

  • Dorsal Interossei (DAB):

    • Origin: Sides of adjacent metacarpals.

    • Insertion: Base of the proximal phalanges and extensor expansions of the 2nd, 3rd, and 4th fingers.

    • Action: Abduct the fingers away from the midline of the hand.

    • Innervation: Ulnar nerve (deep branch).

Innervation of the Fingers

The innervation of the fingers is primarily provided by the median, ulnar, and radial nerves:

• Median Nerve (C5-T1):

  • Innervates: Most of the flexor muscles of the fingers, including the flexor digitorum superficialis, and the lateral two lumbricals.

  • Sensory Innervation: Provides sensation to the palmar aspect of the thumb, index, middle, and lateral half of the ring fingers.

• Ulnar Nerve (C8-T1):

  • Innervates: The hypothenar muscles, the medial two lumbricals, all interossei, and the flexor digitorum profundus for the 4th and 5th fingers.

  • Sensory Innervation: Provides sensation to the medial palm and the palmar and dorsal aspects of the little finger and the medial half of the ring finger.

• Radial Nerve (C5-T1):

  • Innervates: The extensor muscles of the fingers, including the extensor digitorum, extensor indicis, and extensor digiti minimi.

  • Sensory Innervation: Provides sensation to the dorsal surface of the hand and fingers (except the tips of the digits, which are innervated by the median and ulnar nerves).

Blood Supply to the Fingers

The blood supply to the fingers is primarily provided by branches of the radial and ulnar arteries, which anastomose to form two arches:

• Ulnar Artery:

  • The ulnar artery enters the hand and gives rise to the superficial palmar arch, which supplies the medial part of the hand (including the little finger and half of the ring finger).

• Radial Artery:

  • The radial artery contributes to the deep palmar arch, which supplies the thumb and index finger.

Both arteries have anastomoses in the palm and fingers, ensuring that the hand has a continuous blood supply despite possible obstruction or injury to one of the arteries.

Clinical Significance of the Fingers

1. Tendon Injuries

• Flexor tendon injuries (e.g., jersey finger or bowler's finger) can result in the inability to flex the affected finger, especially the DIP joint.

• Extensor tendon injuries can lead to deformities like mallet finger, where the distal phalanx remains in a flexed position due to disruption of the extensor mechanism.

2. Carpal Tunnel Syndrome

• Carpal Tunnel Syndrome (CTS) involves compression of the median nerve, leading to sensory loss