Wrist

The wrist is a complex joint that connects the forearm to the hand, allowing for a wide range of movement. It is composed of multiple bones, including the distal ends of the radius and ulna (forearm bones) and the carpal bones, which form the base of the hand. The wrist plays a vital role in providing stability and mobility for hand movements.

Location

The wrist is located at the junction of the forearm and the hand. It lies between the distal ends of the radius and ulna bones of the forearm and the proximal row of the carpal bones of the hand.

Anatomy of the Wrist

The wrist, or carpus, is a highly complex structure composed of bones, joints, ligaments, tendons, and associated soft tissues. It serves as a connection between the forearm and the hand. Below is a detailed breakdown of its anatomical components:

Bones of the Wrist

The wrist consists of 15 bones, including the distal ends of the forearm bones and the carpal bones.

Forearm Bones

• Radius: The larger forearm bone on the thumb side, forming the primary articulation with the carpal bones.
• Ulna: The smaller forearm bone on the pinky side, separated from the carpal bones by a fibrocartilaginous disc (the triangular fibrocartilage complex, or TFCC).
• Carpal Bones: Eight small, irregularly shaped bones arranged in two rows:

Proximal Row (from lateral to medial)

• Scaphoid: The largest bone in the proximal row, articulating with the radius.
• Lunate: Located between the scaphoid and triquetrum; also articulates with the radius.
• Triquetrum: A pyramidal-shaped bone that articulates with the pisiform.
• Pisiform: A sesamoid bone situated within the tendon of the flexor carpi ulnaris.

Distal Row (from lateral to medial):

• Trapezium: Articulates with the base of the thumb (first metacarpal).
• Trapezoid: A wedge-shaped bone, articulating with the second metacarpal.
• Capitate: The largest carpal bone, positioned centrally, articulating with the third metacarpal.
• Hamate: Features a hook-like projection (hamulus) and articulates with the fourth and fifth metacarpals.

Joints of the Wrist

The wrist comprises multiple articulations that allow for complex movements:

Radiocarpal Joint

• Formed by the distal end of the radius and the proximal row of carpal bones (excluding the pisiform).
• The primary joint responsible for wrist flexion, extension, and lateral movements.

Midcarpal Joint

• Located between the proximal and distal rows of carpal bones.^[6]
• Plays a role in amplifying wrist movements.

Distal Radioulnar Joint

• Articulates between the radius and ulna.
• Facilitates forearm rotation (supination and pronation).

Intercarpal Joints

• Articulations between adjacent carpal bones within each row.
• Stabilized by intercarpal ligaments.

Carpometacarpal Joints (CMC)

• Connect the distal carpal bones to the bases of the metacarpals.
• The CMC joint of the thumb is particularly specialized for its unique range of motion.

Ligaments of the Wrist

The wrist is stabilized by numerous ligaments, which can be categorized into extrinsic and intrinsic types.

• Extrinsic Ligaments: Connect the forearm bones to the carpal bones.
  • Palmar Radiocarpal Ligament: Runs from the radius to the proximal carpal row, providing anterior support.
  • Dorsal Radiocarpal Ligament: Provides posterior support to the wrist.
  • Ulnar Collateral Ligament: Runs from the ulna to the pisiform and triquetrum, supporting the medial side.
  • Radial Collateral Ligament: Extends from the radius to the scaphoid and trapezium, stabilizing the lateral side.
• Intrinsic Ligaments: Connect carpal bones to each other.^[4]
  • These include the scapholunate ligament, which is crucial for wrist stability.

Tendons and Muscles

Tendons crossing the wrist originate from muscles in the forearm. They are organized into two groups:

Flexor Tendons (on the anterior side):

• Flexor Carpi Radialis: Flexes and abducts the wrist.
• Flexor Carpi Ulnaris: Flexes and adducts the wrist.
• Flexor Digitorum Superficialis and Profundus: Flex the fingers.
• Flexor Pollicis Longus: Flexes the thumb.
• Palmaris Longus (if present): Contributes to wrist flexion.

Extensor Tendons (on the posterior side):

• Extensor Carpi Radialis Longus and Brevis: Extend and abduct the wrist.
• Extensor Carpi Ulnaris: Extends and adducts the wrist.
• Extensor Digitorum: Extends the fingers.
• Extensor Pollicis Longus and Brevis: Extend the thumb.^[1]

Retinacula:

The tendons are held in place by strong connective tissues:

• Flexor Retinaculum (Transverse Carpal Ligament): Forms the roof of the carpal tunnel.
• Extensor Retinaculum: Holds the extensor tendons in place.

Nerves

The wrist is innervated by branches of three major nerves:

• Median Nerve: Passes through the carpal tunnel and supplies sensation to the palm and fingers.
• Ulnar Nerve: Passes through Guyon’s canal and supplies sensation to the medial side of the hand.
• Radial Nerve: Supplies sensation to the back of the hand and wrist.

Blood Supply

The wrist’s blood supply comes primarily from the radial and ulnar arteries, which form the superficial and deep palmar arches. Numerous smaller branches supply the bones and soft tissues of the wrist.

Cartilage and Soft Tissue

• Articular Cartilage: Covers the surfaces of the wrist bones, facilitating smooth movements.
• Triangular Fibrocartilage Complex (TFCC): A structure of cartilage and ligaments on the ulnar side of the wrist, providing cushioning and stability.

Function

The wrist serves as a critical interface between the forearm and the hand, facilitating a wide range of movements and functions essential for daily activities, fine motor skills, and power applications. Below is a detailed explanation of its functions:

Movement and Range of Motion

The wrist provides a wide range of movements that enable positioning of the hand for various tasks. These movements include:

• Flexion: Bending the wrist forward, reducing the angle between the forearm and the palm. Essential for activities like gripping, writing, or using tools.^[8]
• Extension: Bending the wrist backward, increasing the angle between the forearm and the palm. Necessary for pushing motions and providing stability during weight-bearing tasks.
• Abduction (Radial Deviation): Tilting the wrist toward the thumb side. Used in activities requiring lateral precision, such as playing a piano or typing.
• Adduction (Ulnar Deviation): Tilting the wrist toward the pinky side. Important for side-to-side adjustments in grip and motion.
• Circumduction: A circular movement combining flexion, extension, abduction, and adduction. Enables smooth, complex wrist motions required for tasks like stirring or drawing.
• Rotation: Although rotation primarily occurs in the forearm (via the radioulnar joint), the wrist contributes to adjusting the orientation of the hand during supination (palm up) and pronation (palm down).

Hand Positioning

The wrist allows precise positioning and angling of the hand, enabling optimal interaction with objects and environments. Its ability to combine movements in multiple planes ensures that the hand can adapt to various tasks, from fine motor actions like threading a needle to larger, forceful activities like hammering.

Force Transmission and Load Bearing

The wrist acts as a stabilizing structure, distributing forces between the hand and forearm. Key functions include:

• Shock Absorption: The wrist absorbs and dissipates forces during weight-bearing activities, such as pushing against a surface or catching a fall.
• Force Distribution: The carpal bones and ligaments evenly distribute loads across the wrist, preventing stress concentration on any single structure.
• Grip Strength: By stabilizing the hand, the wrist plays a crucial role in generating and maintaining grip strength during tasks like lifting, carrying, or holding objects.

Fine Motor Control

The intricate anatomy of the wrist, combined with its range of motion, enables precise hand movements. This is essential for activities like:

• Writing, drawing, and painting.
• Using tools, such as a screwdriver or scissors.
• Playing musical instruments, such as a piano or guitar.
• Typing on a keyboard or using a smartphone.

Interaction with Forearm and Fingers

The wrist coordinates movements of the forearm and fingers, creating a functional unit for various activities. For example:

• Forearm-Wrist Coordination: The wrist adjusts hand position during forearm rotation to align the hand for tasks like turning a doorknob or unscrewing a lid.^[7]
• Finger-Wrist Synergy: Wrist positioning enhances the effectiveness of finger movements, such as extending the wrist to increase grip strength or flexing the wrist to reduce tension on finger tendons during precision tasks.

Stabilization

The wrist stabilizes the hand during both static and dynamic activities. Key stabilization functions include:

• Static Stability: Maintaining a steady hand position during tasks like holding a camera or performing surgery.
• Dynamic Stability: Providing a stable base for rapid or repetitive hand movements, such as playing sports or typing.

Adapting to Varied Tasks

The wrist’s flexibility allows it to adapt to diverse physical tasks:

• Power Movements: Supporting heavy or forceful actions, such as lifting weights or throwing a ball.
• Delicate Movements: Facilitating subtle adjustments required for fine motor skills, such as sewing or assembling small components.

 Grip Modulation

The wrist modulates grip by adjusting its position and tension in the flexor and extensor tendons. For example:

• Strong Grip: Extending the wrist slightly maximizes tension in the finger flexor tendons, enhancing grip strength.^[5]
• Precision Grip: Flexing or abducting the wrist fine-tunes hand positioning for delicate tasks, such as holding a pen or picking up small objects.

Communication and Expression

In addition to mechanical functions, the wrist facilitates non-verbal communication and expression, such as:

• Gestures like waving, pointing, or signaling.
• Artistic movements required for dance or performance.

Clinical Significance

The wrist is a critical joint prone to various injuries and conditions due to its complex anatomy and frequent use in daily activities. Its clinical significance lies in the following areas:

Fractures

• Common wrist fractures include those of the scaphoid and distal radius. These are often caused by falls onto an outstretched hand.
• Scaphoid fractures are particularly significant due to the risk of avascular necrosis caused by its limited blood supply.

Ligament Injuries

• The scapholunate ligament is the most commonly injured ligament, leading to instability and chronic wrist pain.
• Severe trauma can cause tears in the triangular fibrocartilage complex (TFCC), resulting in pain and limited wrist mobility.

Arthritis

Osteoarthritis and rheumatoid arthritis frequently affect the wrist, causing pain, stiffness, and reduced range of motion.^[3]

Carpal Tunnel Syndrome

• Compression of the median nerve within the carpal tunnel can cause pain, tingling, and numbness in the hand, particularly affecting the thumb, index, and middle fingers.
• This is a common condition in individuals performing repetitive hand and wrist motions, such as typing.

Tendonitis and Overuse Injuries

• Inflammation of tendons, such as in De Quervain’s tenosynovitis, can result from repetitive wrist movements.
• Overuse injuries are common in athletes and individuals with occupations involving repetitive wrist strain.

Congenital and Developmental Disorders

Conditions such as Madelung deformity, a growth disturbance of the distal radius, can impair wrist function.

Infections and Tumors

The wrist can be affected by infections such as septic arthritis or by soft tissue and bone tumors, though these are less common.^[2]

Neurological Disorders

Compression of the ulnar nerve at the wrist (Guyon’s canal syndrome) can lead to weakness and sensory deficits in the ring and little fingers.Timely diagnosis and treatment of wrist-related conditions are crucial to preserve its function and prevent long-term complications, as the wrist’s mobility and stability are essential for most hand and forearm activities.