Ulna

Contents

Name of bone

Ulna

Location/Articulation

The ulna is one of the two bones of the forearm, parallel with the radius. It articulates with the:

  • humerus, at the elbow, as a hinge joint to allow flexion and extension
  • radius, near the elbow as a pivot joint, to allow pronation and suppination 
  • distal radius, where it fits into the ulna notch.
  • radius along its length via the interosseous membrane that forms a syndesmoses joint.




Figure 1. Radius, ulna, and humerus



There three important features of the proximal ulna:

  • The olecranon process, onto which the triceps attaches


  • The coronoid process, preventing anterior subluxation of the humerus


  • The semilunar notch, in which the humerus sits

Muscle and ligament attachments

Muscle 

Direction 

Attachment 

Triceps brachii muscle

Insertion

Olecranon process (via common tendon)

Anconeus muscle

Insertion

Olecranon process (lateral aspect)

Brachialis muscle

Insertion

Coronoid process of the ulna

Pronator teres muscle

Origin

Coronoid process (also shares origin with medial epicondyle of the humerus)

Flexor carpi ulnaris muscle

Origin

Olecranon process and posterior surface of ulna (also shares origin with medial epicondyle of the humerus)

Flexor digitorum superficialis muscle

Origin

Coronoid process (also shares origin with medial epicondyle of the humerus and shaft of the radius)

Flexor digitorum profundus muscle

Origin

Coronoid process, anteromedial surface of ulna (also shares origin with the interosseous membrane)

Pronator quadratus muscle

Origin

Distal portion of anterior ulnar shaft

Extensor carpi ulnaris muscle

Origin

Posterior border of ulna (also shares origin with lateral epicondyle of the humerus)

Supinator muscle

Origin

Proximal ulna (also shares origin with lateral epicondyle of the humerus)

Abductor pollicis longus muscle

Origin

Posterior surface of ulna (also shares origin with the posterior surface of the radius bone)

Extensor pollicis longus muscle

Origin

Dorsal shaft of ulna (also shares origin with the dorsal shaft of the radius and the interosseous membrane)

Extensor pollicis brevis muscle

Origin

Dorsal shaft of ulna (also shares origin with the dorsal shaft of the radius and the interosseous membrane)

Extensor indicis muscle

Origin

Posterior surface of distal ulna (also shares origin with the interosseous membrane)

Surface anatomy

The long, narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and dorsal surface. At the extremities the compact layer thins. The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamellæ parallel. From the inner surface of this plate and the compact layer below it, trabeculæ arch forward toward the olecranon and coronoid and cross other trabeculæ, passing backward over the medullary cavity from the upper part of the shaft below the coronoid.

Below the coronoid process there is a small area of compact bone from which trabeculæ curve upward to end obliquely to the surface of the semilunar notch, which is coated with a thin layer of compact bone. The trabeculæ at the lower end have a more longitudinal direction.

The ulna is broader proximally, and narrower distally. Proximally, the ulna has a bony process, the olecranon process, which is a hook-like structure that fits into the olecranon fossa of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus. There is also a radial notch for the head of the radius, and the ulnar tuberosity to which muscles can attach. At the distal end of the ulna is a styloid process.




Figure 2. Surface anatomy

Radiography

Physical examination

Embryology

Anomalies

Injuries/Disorders

Attachments:


ulna.jpg (image/pjpeg)




ulna.png (image/png)




radius_and_ulna.jpg (image/pjpeg)




olecranon fossa.JPG (image/jpeg)




olecranon.JPG (image/jpeg)




coronoid.JPG (image/jpeg)