Hand Anatomy: Understanding the Structure of Your Hand

The hand is a marvel of biological engineering. Understanding its anatomy helps you better recognize your symptoms, understand your injuries, and actively participate in your treatment. As physiotherapists specializing in hand and wrist disorders, we know that this anatomical knowledge improves treatment outcomes.

What are the main structures of the hand?

The hand contains 27 bones (8 carpal bones in the wrist, 5 metacarpals in the palm, and 14 phalanges in the fingers), several joints, stabilizing ligaments, flexor and extensor tendons, as well as 21 intrinsic muscles and 15 extrinsic muscles originating from the forearm.

The 27 Bones of the Hand

The hand skeleton is divided into three distinct groups:

The Carpus (8 wrist bones):

• First row: scaphoid, lunate, triquetrum, pisiform
  
• Second row: trapezium, trapezoid, capitate, hamate

These small bones connect to each other to create the complex mobility of the wrist. The scaphoid is particularly important because it is frequently fractured during falls onto the hand.

The Metacarpus (5 palm bones):
Each metacarpal bone corresponds to a finger. They form the structure of your palm and connect with the carpal bones on one side and the phalanges on the other.

The Phalanges (14 finger bones):

• The fingers (index, middle, ring, little): 3 phalanges each (proximal, middle, distal)
  
• The thumb: 2 phalanges only (proximal and distal)

The Joints

The hand contains many joints that allow for its exceptional mobility:

• Radiocarpal Joint: Between the forearm (radius) and the first row of carpal bones, it allows for wrist movements
• Carpometacarpal Joints: Connect the carpus to the metacarpus
• Metacarpophalangeal Joints (MCP): The "knuckles" visible when you make a fist
• Interphalangeal Joints (IP): Between the finger phalanges

Ligaments, Tendons, and Muscles

Ligaments stabilize the carpal bones:

• Extrinsic ligaments: connect the radius and ulna to the carpus
  
• Intrinsic ligaments: connect the carpal bones to each other (scapholunate, triquetrolunate)

Tendons transmit muscle force to the bones:

• Flexor tendons: located on the palm, allow you to close your hand
  
• Extensor tendons: located on the back of the hand, allow you to open your fingers

The fingers themselves do not contain muscles, only tendons.

Muscles:

• 21 intrinsic muscles: located in the hand, responsible for fine movements
  
• 15 extrinsic muscles: located in the forearm, their tendons cross the wrist to move the fingers

The thumb muscle (thenar) is the largest in the hand and provides the strength for pinching or grasping.

How does the hand work?

The hand allows for strong gripping (grasping heavy objects) and precise gripping (fine manipulations). The thumb performs opposition (a unique movement that allows for pinching), while the intrinsic muscles ensure fine coordination and tactile sensitivity.

The Two Types of Grip

Power Grip:
You use your entire palm and fingers to grasp heavy or bulky objects. This grip mainly involves the extrinsic muscles of the forearm, which generate significant force.

Precision Grip:
You use your fingertips to manipulate small objects or perform delicate tasks. This grip relies on the intrinsic muscles of the hand, which allow for fine control.

Thumb Opposition: A Unique Movement

The thumb has a unique ability among the fingers: opposition. This movement allows the thumb to touch the tip of each of the other fingers, creating the essential pincer grasp (thumb-to-index finger) needed for so many daily tasks.

This exceptional mobility comes from:

• The carpometacarpal joint of the thumb (saddle-shaped)
  
• The powerful thenar muscles
  
• The anatomical position of the thumb (90° relative to the other fingers)

Fine Coordination and Sensitivity

The intrinsic muscles allow for:

• Independent movement of each finger
  
• Coordination between fingers
  
• Precise adjustments to grip strength

The hand also contains countless nerve endings that provide:

• Tactile sensitivity (texture, temperature)
  
• Proprioception (awareness of finger position in space)
  
• Protection (pain detection)

What are Common Hand Injuries?

Frequent injuries include carpal tunnel syndrome (compression of the median nerve), De Quervain's tenosynovitis (inflammation of the thumb extensor tendons), finger sprains (ligament damage), and hand osteoarthritis affecting the joints.

Carpal Tunnel Syndrome

Carpal tunnel syndrome is the most common condition affecting the hand. It occurs when the median nerve is compressed within the carpal tunnel at the wrist.

Typical Symptoms:

• Numbness in the thumb, index, and middle fingers
  
• Nighttime tingling
  
• Weakness in the thumb-index finger pinch
  
• Pain radiating to the forearm

De Quervain's Tenosynovitis

De Quervain's tenosynovitis affects the extensor tendons of the thumb at the wrist. It creates friction between the tendons and the tunnel they slide through.

Common Causes:

• Repetitive movements (texting, computer mouse use)
  
• Repeated twisting movements
  
• Hormonal changes (pregnancy, menopause)

Symptoms:

• Pain on the thumb side of the wrist
  
• Visible swelling
  
• Difficulty pinching or gripping

Finger Sprains

Sprains occur when the ligaments of the interphalangeal joints are stretched or torn, often during sports activities or falls.

Signs of a Sprain:

• Localized pain in the joint
  
• Swelling
  
• Limited movement
  
• Sometimes joint instability

Hand Osteoarthritis

Osteoarthritis affects the cartilage in the joints, particularly:

• The joint at the base of the thumb (thumb CMC joint osteoarthritis)
  
• The distal interphalangeal joints
  
• The MCP joints

It manifests as progressive stiffness, pain with use, and sometimes visible deformities.

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