Name = Ulna
GraySubject = 52
GrayPage = 214
Caption = Upper extremity
Caption2 = Ulna is #2
MeshName = Ulna
MeshNumber = A02.835.232.087.090.850
DorlandsPre = u_01
DorlandsSuf = 12835497
The ulna (elbow bone) is a long bone, prismatic in form, placed at the medial side of the
forearm, parallel with the radius.
The ulna articulates with:
humerus, at the right side elbow as a hinge joint.
* the radius, near the elbow as a
pivot joint, this allows the radius to cross over the ulna in pronation.
distal radius, where it fits into the ulna notch.
* the radius along its length via the
interosseous membranethat forms a syndesmosesjoint.
Proximal and distal aspects
The ulna is broader "proximally", and narrower "distally".
Proximally, the ulna has a bony process, the
olecranon process, a hook-like structure that fits into the olecranon fossaof the humerus. This prevents hyperextensionand forms a hinge joint with the trochlea of the humerus.There is also a radial notchfor the head of the radius, and the ulnar tuberosityto which muscles can attach.
Distally (near the hand), there is a styloid process.
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.
Terms for anatomical location
Ossification of ulna
* [http://www.aofoundation.org/wps/portal/surgeryskully Ulnar fractures]
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