Finger

A finger is one of the five slender, articulated extensions located at the distal end of the human hand. Fingers consist of bones, joints, tendons, ligaments, and muscles, allowing for precise movements. Each finger is covered in highly sensitive skin with numerous nerve endings, enabling tactile sensation. Fingers are classified as digits, with four fingers on each hand alongside an opposable thumb. The fingers are essential for grasping, manipulating objects, and performing fine motor tasks.

Location

Fingers are located on the distal part of the hand, extending from the palm. Each finger begins at the metacarpophalangeal (MCP) joint and ends at the distal phalanges.

Anatomy

The anatomy of the finger is complex and highly specialized, consisting of bones, joints, muscles, tendons, ligaments, nerves, and blood vessels. Each finger is designed to perform precise and coordinated movements. Below is a detailed explanation of its anatomical components:

Bones of the Finger

Fingers are composed of 14 bones known as phalanges, divided into three types:

Proximal Phalanges

The largest segment of each finger, connecting to the metacarpal bones in the palm.

Middle Phalanges

Found in all fingers except the thumb. They are located between the proximal and distal phalanges.

Distal Phalanges

The smallest and most distal bones of the fingers, forming the fingertip.

Each finger has three phalanges (proximal, middle, distal), except for the thumb, which has only two (proximal and distal).

Joints of the Finger

The fingers have joints that provide flexibility and mobility:

Metacarpophalangeal (MCP) Joints

• Located at the base of each finger, connecting the metacarpal bones to the proximal phalanges.
• These are condyloid joints that allow flexion, extension, abduction, and adduction.

Proximal Interphalangeal (PIP) Joints

• Found between the proximal and middle phalanges.
• These are hinge joints, enabling flexion and extension.

Distal Interphalangeal (DIP) Joints

• Located between the middle and distal phalanges.
• These are also hinge joints, allowing flexion and extension.

The thumb has only one interphalangeal (IP) joint, as it lacks a middle phalanx.

Muscles of the Finger

Finger movements are controlled by extrinsic and intrinsic muscles:

Extrinsic Muscles

Originate in the forearm and insert on the fingers.

• Flexor Muscles:
  • • Flexor Digitorum Superficialis: Flexes the MCP and PIP joints.
    • Flexor Digitorum Profundus: Flexes the MCP, PIP, and DIP joints.
• Extensor Muscles:
• • • Extensor Digitorum: Extends the MCP, PIP, and DIP joints.
    • Extensor Indicis: Extends the index finger.
    • Extensor Digiti Minimi: Extends the little finger.
• Intrinsic Muscles:
  • Located entirely within the hand, these muscles contribute to fine motor control.
  • Lumbricals: Flex the MCP joints and extend the IP joints.
  • Interossei:
    • Palmar Interossei: Adduct the fingers.
    • Dorsal Interossei: Abduct the fingers.

Tendons

Tendons connect muscles to bones, transmitting the force required for finger movements.

Flexor Tendons

• Flexor Digitorum Superficialis Tendons: Insert on the middle phalanges to flex the PIP joints.
• Flexor Digitorum Profundus Tendons: Insert on the distal phalanges to flex the DIP joints.

Extensor Tendons

• Run along the dorsal side of the fingers, enabling extension of all finger joints.
• The tendons are enclosed within synovial sheaths, which reduce friction and facilitate smooth movement.

Ligaments

Ligaments provide stability to the finger joints:

Collateral Ligaments

Located on either side of the MCP, PIP, and DIP joints, preventing lateral displacement.

Volar Plate

A thick ligament on the palmar side of each joint, preventing hyperextension.

Transverse Metacarpal Ligament

Connects the heads of the metacarpals, maintaining the alignment of the fingers.

Nerves

The fingers are richly innervated, allowing for precise motor control and tactile sensation. Three major nerves supply the fingers:

Median Nerve

• Innervates the palmar side of the thumb, index, middle, and half of the ring finger.
• Supplies sensation and motor control for fine movements.^[6]

Ulnar Nerve

• Innervates the little finger and half of the ring finger, including both palmar and dorsal sides.
• Controls many of the intrinsic hand muscles.

Radial Nerve

Supplies the dorsal side of the hand, particularly the back of the thumb, index, and middle fingers.

Blood Supply

Blood supply to the fingers is provided by branches of the radial and ulnar arteries:

Digital Arteries:

• Arise from the superficial and deep palmar arches.
• Run along the sides of each finger, forming a rich capillary network for efficient blood flow.

Venous Drainage:

Accomplished through digital veins, which drain into the larger veins of the hand and forearm.

Skin and Sensory Structures

Fingertips:

• Covered in highly sensitive skin with dense concentrations of mechanoreceptors, including Merkel cells, Meissner corpuscles, and Pacinian corpuscles.^[4]
• Fingertips also contain sweat glands but lack hair, enhancing tactile sensation and grip.

Fingernails:

Hard keratinized structures that protect the distal phalanges and enhance tactile feedback.

Function

The fingers are essential for an extensive range of activities, from gross motor actions to highly precise and delicate tasks. They combine flexibility, strength, and sensitivity, enabling interaction with the environment and facilitating communication. Below is a detailed breakdown of the finger’s functions:

Grasping and Holding Objects

Fingers work in coordination with the thumb to create various grips, allowing the hand to grasp, hold, and manipulate objects effectively:

Power Grip

• Fingers curl around an object, and the thumb applies counterpressure (e.g., holding a hammer or bottle).
• The flexor tendons and intrinsic muscles generate the necessary force for strong grips.

Precision Grip

Involves the thumb and one or more fingers working together for tasks requiring fine control (e.g., holding a pen, threading a needle).^[1]

Hook Grip

Fingers form a hook-like structure without involving the thumb (e.g., carrying a bag or suitcase).

Pinch Grip

The thumb and index finger pinch an object (e.g., picking up a small coin).

Fine Motor Skills and Manipulation

Fingers provide the dexterity required for intricate tasks. These skills are critical in activities such as:

• Writing, typing, and drawing.
• Playing musical instruments (e.g., piano, guitar).
• Sewing or assembling small parts.
• Performing medical or technical procedures.

The ability to independently control each finger (e.g., tapping a specific key on a keyboard) relies on precise coordination of tendons and muscles.

Tactile Sensation and Sensory Feedback

Fingers are equipped with highly sensitive skin and dense concentrations of sensory receptors. Key sensory functions include:

Touch Sensation

Fingertips are rich in mechanoreceptors, allowing detection of texture, shape, and surface irregularities.^[8]

Pressure and Vibration

Receptors such as Pacinian corpuscles detect vibrations and subtle changes in pressure, aiding in grip adjustment.

Temperature and Pain

Thermoreceptors and nociceptors in the fingers provide feedback on temperature and potential harm, protecting the hand from injury.

Proprioception

Fingers provide spatial awareness of their position and movement, enabling coordinated actions without direct visual input.^[7]

Communication and Expression

Fingers are vital for non-verbal communication and self-expression:

Gestures:

• Pointing, waving, or counting.
• Expressive movements such as signaling “OK” or forming letters in sign language.

Artistic Expression:

Fingers enable painting, sculpting, or crafting, allowing humans to create and convey emotions through art.

Exploration and Interaction

Fingers act as primary tools for exploring the environment and interacting with objects:

Exploration:

By running fingers over surfaces, individuals can identify objects, measure dimensions, or assess material quality.

Tool Use:

Fingers allow precise handling of tools, such as knives, screwdrivers, or electronic devices.

Self-Care:

Tasks like grooming, eating, and dressing rely heavily on finger dexterity and coordination.^[5]

Force Application

Fingers generate force for activities requiring strength and stability:

• Squeezing or pinching to hold objects tightly.
• Pushing or pulling with control and precision.
• Supporting body weight during tasks like climbing or gripping sports equipment.

Grip Adjustment and Modulation

Fingers continuously adjust grip strength based on the object’s weight, texture, and shape. For example:

• Gripping tightly for heavy objects to prevent slipping.
• Loosening the grip for fragile or delicate items like a piece of glass.

This grip modulation is facilitated by sensory feedback from the fingertips.

Stabilization

Fingers provide stability to the hand during tasks requiring controlled and steady movements. Examples include:

• Stabilizing an object while the other hand performs a task (e.g., holding a nail while hammering).
• Holding objects steady during photography or surgery.^[3]

Adaptation to Diverse Tasks

The fingers are highly versatile and adapt to different types of tasks, including:

• Gross movements: Holding heavy tools, lifting, or throwing.
• Delicate movements: Operating touch screens, zipping a jacket, or turning pages.

Emotional and Social Connection

Fingers contribute to emotional expression and social interaction through actions such as:

• Touch: Caressing or holding hands conveys comfort and connection.
• Applause: Clapping expresses appreciation or approval.
• Gestures: Specific finger movements, such as a thumbs-up, have cultural and social significance.

Specialized Functions

Fingers are crucial for specialized tasks in various fields:

• Medical: Performing surgeries or using instruments like scalpels.
• Technological: Operating devices such as keyboards, smartphones, or gaming controllers.
• Sports: Activities like climbing, basketball, or racquet sports depend on finger strength and coordination.

Clinical Significance

The fingers are highly functional and complex structures, making them vulnerable to various injuries and conditions. Their clinical significance includes:

Injuries

• Fractures: Common in the phalanges due to trauma or falls.
• Dislocations: Can occur at the MCP, PIP, or DIP joints, often from sports or accidents.
• Tendon Injuries: Flexor or extensor tendon ruptures can impair movement (e.g., mallet finger or trigger finger).^[2]

Arthritis

• Osteoarthritis: Leads to joint pain and stiffness, particularly in the DIP joints.
• Rheumatoid Arthritis: Causes joint deformities such as swan-neck or boutonniere deformities.

Nerve Disorders

Carpal Tunnel Syndrome: Affects the median nerve, causing numbness and weakness in the thumb, index, and middle fingers.

Ulnar Nerve Compression: Impacts the ring and little fingers, leading to sensory and motor deficits.

Congenital Abnormalities

Conditions such as syndactyly (fused fingers) or polydactyly (extra fingers) may require surgical correction.