First metacarpal bone

Bone of the hand

The first metacarpal bone is one of the five metacarpal bones of the hand. It is unique among the metacarpals due to its role in the thumb's wide range of motion, which is essential for opposition and prehensile grip.

Anatomy

The first metacarpal bone is the shortest and most robust of the metacarpals. It is located at the base of the thumb and articulates proximally with the trapezium bone of the wrist and distally with the proximal phalanx of the thumb.

Structure

The first metacarpal consists of a base, shaft, and head:

• Base: The base of the first metacarpal is saddle-shaped, allowing for the unique saddle joint articulation with the trapezium. This joint is crucial for the thumb's wide range of motion.
• Shaft: The shaft is slightly curved and robust, providing strength and support for thumb movements.
• Head: The head of the first metacarpal is rounded and articulates with the proximal phalanx of the thumb, forming the metacarpophalangeal joint.

File:First metacarpal bone.png

Diagram of the first metacarpal bone.

Muscle Attachments

Several muscles attach to the first metacarpal, contributing to thumb movement:

• The abductor pollicis longus inserts on the lateral side of the base, aiding in thumb abduction.
• The opponens pollicis attaches along the shaft, facilitating thumb opposition.

Function

The first metacarpal bone plays a critical role in the function of the thumb, enabling a wide range of movements including flexion, extension, abduction, adduction, and opposition. These movements are essential for grasping and manipulating objects, making the thumb a key component of the prehensile hand.

Clinical Significance

Injuries to the first metacarpal bone can significantly impair hand function. Common injuries include:

• Fractures: The first metacarpal is susceptible to fractures, often resulting from falls or direct trauma. A common type of fracture is the Bennett's fracture, which involves a fracture-dislocation at the base of the first metacarpal.
• Arthritis: The carpometacarpal joint of the thumb is a common site for osteoarthritis, leading to pain and reduced mobility.

Related Pages

• Metacarpal bones
• Thumb
• Opposable thumb
• Bennett's fracture
• Carpometacarpal joint