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Upper extremity
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The ('''elbow bone''') is a long bone,
Prism atic in form, placed at the
Medial side of the
Forearm , parallel with the
Radius .
The ulna articulates with:
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 Fossa of the . 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
Styloid Process .
It is divisible into a body and two extremities.
- Upper Extremity Of Ulna : of great thickness and strength, forms a large part of the elbow-joint; the bone diminishes in size from above downward,
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.
