First metacarpal bone

The first metacarpal bone is the bone in the hand that is located at the base of the thumb. It is unique among the metacarpal bones due to its distinct shape and function, allowing for the wide range of motion of the thumb.

Anatomy

Palmar view of the first metacarpal bone of the left hand.

The first metacarpal bone is shorter and thicker than the other metacarpal bones. It articulates proximally with the trapezium bone and distally with the proximal phalanx of the thumb. The base of the first metacarpal is saddle-shaped, which allows for the opposable thumb movement.

Structure

Diagram of the first metacarpal bone.

The first metacarpal bone consists of a base, a shaft, and a head. The base is broad and articulates with the trapezium. The shaft is slightly curved and the head is rounded, forming the knuckle of the thumb.

Articulations

The first metacarpal bone articulates with the trapezium at the carpometacarpal joint, which is a saddle joint. This joint allows for a wide range of thumb movements, including flexion, extension, abduction, adduction, and opposition.

Function

The primary function of the first metacarpal bone is to support the thumb and enable its wide range of motion. This bone plays a crucial role in the prehensile grip and precision grip of the hand, allowing humans to perform complex tasks.

Development

The first metacarpal bone ossifies from two centers: one for the shaft and one for the base. Ossification begins in the shaft during fetal development and in the base during early childhood.

Clinical significance

X-ray showing a Rolando fracture of the first metacarpal.

Fractures of the first metacarpal bone can occur due to trauma. Common types of fractures include the Bennett's fracture and the Rolando fracture. These fractures can affect the function of the thumb and may require surgical intervention.

Imaging

X-ray of the first metacarpal bone.

Another view of the first metacarpal bone.

Imaging techniques such as X-rays are used to diagnose fractures and other conditions affecting the first metacarpal bone. These images help in planning treatment and assessing the healing process.

Related pages

• Metacarpal bones
• Trapezium bone
• Opposable thumb
• Bennett's fracture
• Rolando fracture