2025 Comprehensive Guide to Hand and Wrist Bones: Structure, Function & Common Injuries

The human hand is a marvel of anatomy, composed of three main parts: the wrist, palm, and fingers. The wrist contains numerous small bones and joints that provide remarkable flexibility and strength, enabling complex movements. It also includes the distal ends of the forearm bones, the radius and ulna. The palm houses five metacarpal bones that connect to the fourteen bones of the fingers, forming the framework for dexterity and grip.

Let's delve deeper into each component.

Carpal Bones of the Wrist

The wrist comprises eight small bones known as the carpal bones or carpus. These uniquely shaped bones link the hand to the forearm’s radius and ulna, contributing to the wrist’s strength and flexibility. Unlike a joint with only one or two large bones, this cluster allows for a wide range of motion.

The eight carpal bones include:

• Scaphoid: Boat-shaped bone located beneath the thumb.
• Lunate: Crescent-shaped bone adjacent to the scaphoid.
• Trapezium: Rounded square bone positioned above the scaphoid and under the thumb.
• Trapezoid: Wedge-shaped bone next to the trapezium.
• Capitate: Oval or head-shaped bone centrally located in the wrist.
• Hamate: Wedge-shaped bone beneath the pinky side of the hand.
• Triquetrum: Pyramid-shaped bone beneath the hamate.
• Pisiform: Small, pea-shaped sesamoid bone resting atop the triquetrum.

Wrist Joint Anatomy

The wrist features three primary joints, enhancing its stability and enabling a broad spectrum of movements, including flexion, extension, rotation, and side-to-side motion.

• Radiocarpal Joint: Connects the radius to the scaphoid, lunate, and triquetrum bones, located on the thumb side.
• Ulnocarpal Joint: Links the ulna with the lunate and triquetrum bones on the pinky side.
• Distal Radioulnar Joint: Connects the distal ends of the radius and ulna without involving carpal bones.

Metacarpal Bones of the Hand

The palm contains five metacarpal bones, each corresponding to a finger, consisting of a base, shaft, and head. The first metacarpal, associated with the thumb, is shorter and thicker, offering the greatest mobility. The remaining metacarpals (second to fifth) move collectively, with the fourth and fifth being the most flexible among them.

• First (Thumb) Metacarpal: Shortest and thickest; articulates with the trapezium bone.
• Second (Index) Metacarpal: Longest, connecting to trapezium, trapezoid, and capitate bones.
• Third (Middle) Metacarpal: Articulates with the capitate bone.
• Fourth (Ring) Metacarpal: Connects with capitate and hamate bones.
• Fifth (Pinky) Metacarpal: Smallest; articulates with the hamate bone.

Phalanges: The Finger Bones

The fingers contain 14 phalanges: each finger has three (proximal, middle, distal), while the thumb has two (proximal and distal). These bones facilitate intricate finger movements essential for gripping and manipulation.

• Proximal Phalanx: Largest phalanx; forms joints with metacarpals and middle phalanges.
• Middle (Intermediate) Phalanx: Connects proximal and distal phalanges.
• Distal Phalanx: Supports the fingernail and fingertip’s sensitive skin.

Finger Joint Structure and Function

Finger joints enable a wide range of movements necessary for tasks like pinching and grasping. According to the American Society for Surgery of the Hand (ASSH), the key finger joints include:

• Carpometacarpal (CMC) Joint: Between distal carpal bones and metacarpal bases.
• Metacarpophalangeal (MCP) Joint: The knuckle joint allowing multiple directional movements.
• Proximal Interphalangeal (PIP) Joint: Allows finger bending and extension.
• Distal Interphalangeal (DIP) Joint: Located near the fingertip.

The thumb’s specialized joints include:

• Trapeziometacarpal (TMC) Joint: Provides thumb’s extensive movement and flexibility.
• Metacarpophalangeal (MCP) Joint: Facilitates pinching and gripping.
• Interphalangeal (IP) Joint: Located near the thumb’s tip.

Common Injuries and Conditions Affecting the Wrist and Hand Bones

Injuries and disorders can impact the ligaments, tendons, muscles, and nerves of the hand and wrist. Some prevalent conditions include:

• Sprains: Ligament tears or stretches caused by overstretching, trauma, or falls.
• Ulnocarpal Impaction Syndrome: Occurs when the ulna bone is longer than the radius, often post-fracture, leading to joint instability.
• Arthritis: Joint inflammation causing pain, which may result from wear and tear or autoimmune conditions like rheumatoid arthritis.
• Fractures: Breaks in any wrist, hand, or finger bone due to trauma.
• Repetitive Stress Injuries: Result from repeated motions such as typing or sports, causing pain, swelling, and numbness.
• Carpal Tunnel Syndrome: Compression of the median nerve, often linked to repetitive wrist movements, hypertension, or diabetes.
• Boxer’s Fracture: Fracture of the fourth or fifth metacarpal caused by punching a hard object.
• Jersey Finger: Tendon injury near the fingertip, commonly requiring surgery.
• Mallet Finger: Tendon injury affecting finger extension, causing pain and swelling.
• Trigger Finger: Stenosing tenosynovitis causing finger locking, often seen in diabetes and rheumatoid arthritis patients.

Summary

The human hand’s 27 bones—comprising 8 carpals, 5 metacarpals, and 14 phalanges—work in harmony with joints to provide the flexibility, strength, and precision necessary for countless daily activities. Understanding this intricate anatomy helps in recognizing common injuries and maintaining optimal hand health.

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