View source for Ulna

{{Infobox Bone |
  Name              = Ulna |
  Latin             = |
  GraySubject       = 52 |
  GrayPage          = 214 |
  Image             = Illu_upper_extremity.jpg |
  Caption           = Upper extremity  |
  Image2            = Carpus.png |
  Caption2          = Ulna is #2 |
  Articulations     = |
  MeshName          = Ulna |
  MeshNumber        = A02.835.232.087.090.850 |
  DorlandsPre       = u_01 |
  DorlandsSuf       = 12835497  |
}}

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==Overview==
The '''ulna''' ('''elbow bone''') is a long bone, [[prism (geometry)|prism]]atic in form, placed at the [[Anatomical terms of location#Relative directions|medial]] side of the [[forearm]], parallel with the [[radius (bone)|radius]]. 

==Articulations==
The ulna articulates with:
* the [[humerus]], at the right side [[Elbow-joint|elbow]] as a [[hinge joint]].
* the [[Radius (bone)|radius]], near the elbow as a [[pivot joint]], this allows the radius to cross over the ulna in [[pronation]].
* the [[distal radius]], where it fits into the ulna notch.
* the radius along its length via the [[interosseous membrane]] that forms a [[syndesmoses]] joint.

==Proximal and distal aspects==
The ulna is broader ''proximally'', and narrower ''distally''.

Proximally, the ulna has a bony [[Process (anatomy)|process]], the [[olecranon process]], 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.

Distally (near the hand), there is a [[Ulnar styloid process|styloid process]].

==  Structure ==
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.

== See also ==
*[[Bone#Terminology|Bone terminology]]
*[[Terms for anatomical location]]
*[[Ossification of ulna]]

==Additional images==
<gallery>
 Image:Ulna ant.jpg|Ulna l. dx. - ant. view 
 Image:Ulna med.jpg|Ulna l. dx. - lat. view 
 Image:RightHumanPosteriorRadiusUlna.jpg|Right posterior human radius and ulna
 Image:Gray213.png|Bones of left forearm. Anterior aspect.
 Image:Gray214.png|The radius and ulna of the left forearm, posterior surface. 
 Image:Gray329.png|Left elbow-joint, showing anterior and ulnar collateral ligaments.
 Image:Gray417.png|Cross-section through the middle of the forearm. 
 Image:Gray420.png|The Supinator.
 Image:Gray421.png|Transverse section across distal ends of radius and ulna.
</gallery>

== External links ==
* [http://www.aofoundation.org/wps/portal/surgeryskully Ulnar fractures]

{{Gray's}}
{{Bones of upper extremity}}
[[Category:Long bones]]
[[Category:Bones of thoracic limb]]

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