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Anatomy Of The Ulna And Radius

By Tyler Woodward

The ulna & radius are the two bones which make up the lower-arm and are hosts to all the muscles and joints which allow us to articulate our fingers and move our wrist. Keep reading to learn more about these essential bones.


Ulna And Radius Anatomy:

Anatomy of The ulna and radius

Both the ulna and the radius run from the wrist to the elbow, but there are a number of differences between them. The ulna is longer than the radius and is primarily responsible for supporting the lower arm. The radius on the other hand is able to rotate around the ulna allowing our hands to pronate and supinate.

Both the ulna and the radius have a number of attachment points for muscles and bones:

The Ulna

  • The Trochlear Notch - This is a round notch in which the head of the humerus, the upper-arm bone, fits in.
  • Coracoid Process - This is a triangular shaped area which the radius moves along laterally
  • Olecranon - This is the point area of the elbow and also where the tricep attaches to
  • Supinator Crest - This is the insertion of the supinator muscle
  • Ulnar Tuberosity - This is the insertion of the brachialis muscle
  • The Shaft Of The Ulna - The shaft of the ulna starts out nearly cylindrical near the top, but becomes increasingly triangular towards the bottom. The shaft of the ulna is also thicker than that of the radius.
  • Head Of Ulna - A pointy head that articulates with the radius

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The Radius:

  • Tuberosity - The origin point of the biceps brachii
  • Pronator Tubercle - The insertion point of the pronator teres muscle
  • Ulnar Notch - A notch that articulates with the ulna, the bump on the outside of your wrist
  • Styloid Process - The bump that you can feel underneath the thumb
  • Head Of Radius - A spherical shaped bone that articulates with the ulna and humerus

Both the ulna and radius also share the interosseous membrane which is a layer of strong connective tissue that holds the two bones together.

*Articulates* - Moves With

Ulna & Radius Functions:

ulna and radius functions

The Ulna is primarily responsible for supporting the lower-arm and is a relatively rigid bone that does not move much. The ulna is the longer of the two bones and attaches directly to the humerus and the carpal (wrist) bones, but is not responsible for any of the joint articulations of the wrist or elbow.

The radius on the other hand is what allows us to move or rotate our elbows. The ball-shaped socket at the head of the radius which attaches to the humerus allows the forearm to rotate side-to-side around the fixed ulna.


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