Hand & Wrist Anatomy

The human hand is a remarkable structure made up of 27 bones, 27 joints, 34 muscles, over 100 ligaments and tendons, and countless blood vessels and nerves. The hands enable us to perform intricate daily activities such as writing, driving, cooking, and countless fine motor tasks. Understanding normal hand and wrist anatomy helps patients better appreciate the complexity of these structures and the conditions that can affect them.

Bones of the Hand and Wrist

The skeletal framework of the hand and wrist consists of multiple bone groups:

• Carpal Bones (Wrist) - Eight small bones arranged in two rows that connect the forearm to the hand. These include the scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, and hamate
• Metacarpal Bones (Palm) - Five long bones that form the palm of the hand, numbered from the thumb side (first metacarpal) to the pinky side (fifth metacarpal)
• Phalanges (Fingers) - The bones in the fingers and thumb. Each finger has three phalanges (proximal, middle, and distal), while the thumb has only two (proximal and distal)

The wrist connects to the radius and ulna bones of the forearm, forming the radiocarpal joint that allows wrist movement.

Joints of the Hand

Multiple joints provide the hand's incredible range of motion:

• Metacarpophalangeal (MCP) Joints - The knuckle joints where the metacarpals meet the phalanges. These act as hinges when bending and straightening fingers
• Proximal Interphalangeal (PIP) Joints - The first joints in the fingers, allowing bending closer to the palm
• Distal Interphalangeal (DIP) Joints - The joints closest to the fingertips
• Carpometacarpal (CMC) Joints - Where the metacarpals meet the carpal bones, particularly important for thumb mobility

Soft Tissues - Ligaments and Cartilage

Ligaments are tough, rope-like tissues connecting bones and providing joint stability:

• Collateral Ligaments - Located on both sides of each finger joint, preventing abnormal sideways bending
• Volar Plate - The strongest hand ligament on the palm side of PIP joints, preventing hyperextension (backward bending)
• Articular Cartilage - Smooth tissue covering bone ends at joints, acting as a shock absorber and allowing frictionless movement

Muscles of the Hand

Hand muscles are divided into two groups:

• Intrinsic Muscles - Small muscles originating within the hand itself, responsible for fine motor control such as writing, typing, and playing instruments. Include the lumbricals, interossei, and thenar/hypothenar muscles
• Extrinsic Muscles - Larger muscles originating in the forearm with long tendons extending into the hand, responsible for powerful gripping and gross hand movements

Each finger is controlled by six muscles (three extrinsic and three intrinsic), working in precise coordination.

Tendons of the Hand

Tendons connect muscles to bones, transmitting force to create movement:

• Flexor Tendons - Located on the palm side, these bend the fingers and thumb
• Extensor Tendons - Located on the back of the hand, these straighten the fingers

Flexor tendons pass through protective sheaths with synovial fluid for smooth gliding during movement.

Nerves of the Hand

Three major nerves provide sensation and motor control:

• Median Nerve - Passes through the carpal tunnel at the wrist, providing sensation to the thumb, index, middle, and part of the ring finger. Controls thenar muscles for thumb opposition
• Ulnar Nerve - Travels through Guyon's canal at the wrist, providing sensation to the little finger and half of the ring finger. Controls many intrinsic hand muscles
• Radial Nerve - Provides sensation to the back of the hand, thumb, index, and middle fingers. Controls wrist and finger extension

Blood Vessels

Rich blood supply ensures hand function and healing:

• Radial Artery - The largest artery, traveling across the wrist near the thumb where pulse is measured
• Ulnar Artery - Travels alongside the ulnar nerve through Guyon's canal

These arteries form arches in the palm that branch to supply blood to all fingers.

Bursae

Fluid-filled sacs called bursae reduce friction between tendons and surrounding structures, containing lubricating synovial fluid to facilitate smooth tendon gliding.