Ulna bone

Ulna

File:Ulna - anterior view.png
Anterior view of the left ulna
Latin	ulna
Articulations	Humerus, Radius
Precursor	Lateral plate mesoderm
System	Skeletal system

The ulna is one of the two long bones in the forearm, the other being the radius. It is located on the medial side of the forearm when in the standard anatomical position, which is the side closest to the body. The ulna is a critical component of the skeletal system, providing structural support and enabling a wide range of movements in conjunction with the radius.

Anatomy

The ulna is a long bone that is divided into three main parts: the proximal end, the shaft, and the distal end.

Proximal End

The proximal end of the ulna features several important structures:

• Olecranon: This is the prominent, curved bony projection at the top of the ulna, which forms the point of the elbow. It serves as the attachment site for the triceps brachii muscle.
• Coronoid Process: A triangular eminence projecting forward from the anterior proximal portion of the ulna, it fits into the coronoid fossa of the humerus when the elbow is flexed.
• Trochlear Notch: A large, C-shaped notch that articulates with the trochlea of the humerus to form the elbow joint.
• Radial Notch: A small depression on the lateral side of the ulna that articulates with the head of the radius, allowing for the pivoting motion of the forearm.

Shaft

The shaft of the ulna is triangular in cross-section and has three borders and three surfaces:

• Anterior Border: Sharp and prominent, providing attachment for the interosseous membrane.
• Posterior Border: Rounded and less distinct.
• Interosseous Border: Faces the radius and provides attachment for the interosseous membrane.

Distal End

The distal end of the ulna is smaller and features:

• Head of Ulna: A small, rounded structure that articulates with the ulnar notch of the radius.
• Styloid Process: A pointed projection that provides attachment for the ulnar collateral ligament of the wrist.

Function

The ulna plays a crucial role in the function of the forearm and hand. It acts as a stabilizing structure for the forearm, allowing for the attachment of muscles that facilitate movements such as flexion, extension, pronation, and supination. The ulna, in conjunction with the radius, enables the rotation of the forearm, which is essential for various activities such as turning a doorknob or using a screwdriver.

Development

The ulna develops from the lateral plate mesoderm during embryogenesis. Ossification begins in the fetal period and continues into adolescence. The primary ossification center appears in the shaft, while secondary centers appear in the olecranon and the distal end.

Clinical Significance

Fractures of the ulna are common, often occurring in conjunction with fractures of the radius. The most common type of fracture is the "nightstick fracture," which is an isolated fracture of the ulna typically resulting from a direct blow. Treatment depends on the severity and location of the fracture and may involve immobilization or surgical intervention.

Also see

• Radius (bone)
• Humerus
• Elbow joint
• Forearm
• Skeletal system