The ulna is the medial bone of the forearm, and is homologous with the fibula of the lower limb. This along with other bone called radius connects elbow with radius. It has upper and lower ends a shaft.
The Upper End
The upper end presents the olecranon and coronoid processes, and the trochlear and radial notches.
1. The olecranon process projects upwards from the shaft. It ahs superior, anterior, posterior, medial and lateral surfaces. The anterior surface is articular: it forms the upper part of the trochlear notch. The posterior surface forms a triangular subcutaneous area which is separated from the skin by a bursa.
Inferiorly it is continous with the posterior border of the shaft of the ulna. The upper part forms the point of the elbow. The medial surface of the shaft. The lateral surface is continous inferiorly with the posterior surface of the shaft.
2. The coronoid process projects forwards from the shaft just below the olecranon and has four surfaces, superior, anterior, medial and latera. The supeiro surface forms the lower part of the trochlear notch. The anterior surface is triangular and rough. Its lower corner forms the ulnar tuberosity.
The upper part of its lateral surface is marked by the radial notch for the head of the radius. The annular ligament is attached to the anterior and posterior margins of the notch. The lower part of the lateral surface forms a depressed area (to accommodate the radial tuberosity). It is limited behind by a ridge called the supinator crest.
3. The trochlear notch forms an articular surface that articulates with the trochlea of the humerus to form the elbow joint.
4. The radial notch articulates with the head of the radius to form the superior radioulnar joint.
The Shaft
The Shaft has three borders and three surfaces.
1. The interosseus (or lateral) border is sharpest in its middle two fourths. Inferiorly it can be traced to the lateral side of the head. Superiorly it is continuous with the supinator crest.
2. The anterior border is thick and rounded. It begins above on the medial side of the ulnar tuberosity, passes backwards in its lower one third, and terminates at the medial side of the styloid process.
Text adapted from: Human Anatomy by BD Chaurasia
Image Credit: Wikipedia
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ur xplanatin is good…
But i wud lik to kno de exact reason, wy the Radius is said to be homologous wit tibia nd the Ulna wit Fibula..???
As soon as possible pls…
And i wud be gr8full, if u cud mail me tat!!!!
Thanks…
Dr Arun Pal Singh Reply:
January 26th, 2010 at 9:21 am
@Aftab Hussain,
To understand this you would need to understand that lower limb has rotated 180 degrees during the development.
Thus medial structures on the arm are homologous to lateral structures of leg.
hence ulna homologous to fibula.
thanks!!
in what way ulna is homologous to fibula
Dr Arun Pal Singh Reply:
March 31st, 2011 at 10:09 am
@s khan,
Consider the lower limb rotated by 180 degree and concept of two bones being homologous becomes obvious.
I had trama to my hands, well they were tied in a hospital and my both hands had got blue. they were like that for at least 3 hrs . I now have severe pain even after a year. I have the x-rays and one hand looks all sqwished together and other looks somewhat normal, one of the bones i think its the ulna is pushed to left. the report is saying in my left hand is Chondrocalcinosis. no mention of right hand. all test results are coming in normal expect the intake of the wrist area is slower , i guess its the blood flow. any suggestions. I want to get a second opionion on the xrays i just got . My right hand is worse then left. swollen all the time by thumb area.
Dr Arun Pal Singh Reply:
May 13th, 2011 at 8:29 pm
@Julie,
If you are looking for professional opinion you would need to see a doctor in person.
If you are looking for some information on some topic, you can let me know.
hello….i would like to know how to distinguish between right and left ulna…
Dr Arun Pal Singh Reply:
June 14th, 2011 at 1:03 am
@vivi,
Landmarks help you to identify. Styloid is on medial side and humeral notch faces anterior etc etc.
material is incomplete..
Dr Arun Pal Singh Reply:
September 28th, 2011 at 2:24 pm
@A.Harshavardhan reddy,
It might be from anatomist’s point of view. I agree.