M01.03.016 The Hand

The bones of the hand provide structural support and enable a wide range of movements. They are categorized into three main types:

1. Carpal Bones (wrist) – Eight irregularly shaped bones.
2. Metacarpals (palm) – Five bones, each associated with a digit.
3. Phalanges (fingers) – Bones of the digits. The thumb has two phalanges, while the other fingers have three each.

Key Functions of Hand Bones

• Support the soft tissues of the hand.
• Facilitate fine motor skills.
• Enable articulation for movements like gripping and grasping.

Detailed Anatomy

1. Carpal Bones

The carpal bones are eight irregularly shaped bones organized into two rows:

• Proximal Row: Scaphoid, Lunate, Triquetrum, Pisiform (sesamoid bone).
• Distal Row: Trapezium, Trapezoid, Capitate, Hamate (with the ‘hook of hamate’).

Articulations:

• Proximal row: Scaphoid and lunate articulate with the radius to form the radiocarpal joint (wrist joint).
• Distal row: Articulate with metacarpals at the carpometacarpal joints.

Special Feature:
The carpal bones form an arch in the coronal plane. The flexor retinaculum spans this arch, creating the carpal tunnel, which allows tendons and nerves to pass through.

Clinical Relevance: Scaphoid Fracture

• Cause: Commonly occurs from a fall on an outstretched hand (FOOSH).
• Symptoms: Pain and tenderness in the anatomical snuffbox.
• Risk: Avascular necrosis due to retrograde blood supply entering at the distal end.
• Complication: Missed fractures may lead to osteoarthritis of the wrist.

2. Metacarpal Bones

The metacarpals are five long bones in the palm, numbered I to V (thumb to little finger). Each consists of:

• Base (proximal).
• Shaft.
• Head (distal).

Articulations:

• Proximally with the carpal bones.
• Distally with the proximal phalanges.

Muscle Attachments:
The concave medial and lateral surfaces provide attachment points for interossei muscles.

Clinical Relevance: Fractures of the Metacarpals

1. Boxer’s Fracture:
   • Location: 5th metacarpal neck.
   • Cause: Punching a hard object.
   • Consequence: Angulation and shortening of the little finger.
2. Bennett’s Fracture:
   • Location: Base of the 1st metacarpal.
   • Cause: Forced hyperabduction of the thumb.
   • Complication: Joint instability, often requiring surgical repair.

3. Phalanges

The phalanges are the bones of the fingers.

• Thumb: Two phalanges (proximal and distal).
• Other fingers: Three phalanges each (proximal, middle, and distal).

Key Points to Remember

1. Carpal Tunnel: Protects vital structures like nerves and tendons in the wrist.
2. Scaphoid Fracture: High risk of avascular necrosis due to retrograde blood supply.
3. Metacarpal Fractures:
   • Boxer’s fracture involves the 5th metacarpal.
   • Bennett’s fracture affects the 1st metacarpal and often requires surgical intervention.
4. Phalanges: The thumb has two; all other fingers have three.