Ulna

Which type of bone is Ulna? Where is it located?

Ulna is a long bone. It is the located on the medial  side of forearm.

What are the parts of Ulna?

Like any other long bone ulna also has  two ends and an intervening shaft.

• Upper end : is expanded , irregular , hook like and presents a notch ( trochlear notch) which faces anteriorly.
• Shaft: has three borders ( anterior, interosseous and posterior ) and three surfaces ( anterior, medial and posterior).
• Lower end:  has small round head and a bony projection from posteromedial aspect called styloid process.

Describe the upper and lower ends of Ulna.

Upper end of Ulna: has 2 processes (olecranon and coronoid) and 2 notches (trochlear and radial).

• Olecranon process: Has superior, anterior, posterior, medial and lateral surfaces. Anterior surface forms upper part  of trochlear notch.
• Coronoid process: projects anteriorly from the upper part of shaft. It has four surfaces i.e. superior, anterior, medial and lateral.Lower part of anterior surface has a rough area called ulnar tuberosity.
• Trochlear notch: articulates with trochlea of humerus.
• Radial notch: is present on the lateral surface of coronoid process. It articulates with the head of radius.

Lower end of Ulna

• •  It has small round head of ulna which articulates with ulnar notch at lower end of radius.
  • Styloid process projects downwards from posteromedial aspect of lower end.

How will you determine the side of Ulna?

Ulna should be held vertically in such a way that

• • The expanded, irregular hook like end should be directed upwards.
  • Concavity of trochlear notch should face anteriorly.
  • The sharp interosseous  border should be directed laterally.

How will you hold Ulna in anatomical position? 

Hold ulna vertically so that the trochlear notch faces anteriorly, sharp interosseous border laterally and round head of the ulna is directed inferiorly.

Name the muscles attached to ulna.

The following muscles are attached to ulna:

Upper end of ulna

• Anterior surface of coronoid process  including ulnar tuberosity: Brachialis.
• Medial margin of coronoid process: ulnar head of flexor digitorum superficialis and pronator teres.
• Triangular area below radial notch and supinator crest: Supinator.
• Upper surface (posterior part) of olecranon process :  Triceps.
• Lateral surface of olecranon process and upper part of posterior surface of shaft: Anconeus.

Shaft of ulna

• Anterior and medial surface (upper 3/4th) : Flexor digitorum profundus.
• Oblique ridge on anterior surface ( lower 1/4) : Pronator quadratus.
• Posterior surface from above downwards: 3 muscles- Abductor pollicis longus, extensor pollicis longus, extensor indices.

How does ulna ossify? Which is the growing end of ulna?

Ulna ossifies from 3 ossification centers. One primary center of ossification for the shaft. Two secondary centers, one for each end. Lower end is the growing end.