ULNA BONE
INTRODUCTION FOR ULNA BONE
– Ulna bone is a medial bone of forearm
-The ulna is one of two bones of forearm, and the other one is radius.
-It forms the elbow joint with the humerus and also proximally and distally it articulates with the radius .
– In the anatomical position of hand It is located in the medial forearm .
-It is the larger of the two forearm bones.
– It is homologous to fibula of lower limb.
– It has : Upper end
Lower end
Shaft.
• Side determination
1) Upper end
– Hook like
– Concavity directs forward
2) Shaft
– Lateral border is crest like and sharp.
3) Styloid process lies posteromedial to rounded head of ulnar bone at its lower end.
• FEATURES
• Upper end of ulna bone
– It has,
√ the olecranon and the Coronoid processes
√ the Trochlear and radial notches
1) The olecranon process
– Projects upwards from shaft.
– It has ,
√ Superior surface
√ Anterior surface
√ Posterior surface
√ medial surface
√ Lateral surface
* The anterior surface :
– Articular
– It forms upper part of Trochlear notch.
* The posterior surface :
– It forms a triangular subcutaneous area and is separated from skin by the bursa.
– It continuous with posterior border of the shaft of ulna inferiorly.
– It’s upper part forms a point of eblow.
* The medial surface :
– Continuous with medial surface of the shaft inferiorly.
* The lateral surface :
– Smooth
– Continues as posterior surface of shaft.
* The superior surface :
– Posterior part shows a roughened area.
2) The Coronoid process
– It projects forwards from shaft just below the olecranon process.
– It has ,
√ Superior surface
√ Anterior surface
√ Medial surface.
√ Lateral surface
* Superior surface
– Forms lower part of Trochlear notch.
* Anterior surface :
– Triangular and rough
– Lower corner forms the ulnar tuberosity.
* Lateral surface :
– Upper part :
It is marked by radial notch for head of radius.
Annular ligament is attached to anterior and posterior margins of the notch.
– Lower part :
Forms a depressed area for accomodation of radial tuberosity .
Behind it has a supinator crest.
* Medial surface :
– Continuous with medial surface of shaft.
3) The Triangular notch
– Forms a articular surface which Articulates with Trochlea of humerus to form elbow joint.
4) The radial notch
– Articulates with radial head to form Superior radioulnar joint.
• Shaft of ulna bone
– It has 2 borders and 3 surfaces.
* Borders
1) The lateral or interosseous border
– Sharpest in middle 2/4 th
– Inferiorly : traced to lateral side of head.
– Superiorly : Continuous with supinator crest.
2) The anterior border
– Thick and rounded.
– It begins on medial side of ulnar tuberosity above , then passes backwards in its lower 1/3 rd.
– It terminates at styloid process ( medial side ).
3) The posterior border
– It is subcutaneous
– It begins at the apex of the triangular subcutaneous area at the back of olecranon
– Terminates at base of styloid process.
* Surfaces
1) The anterior surface :
– It lies between anterior and lateral border.
– A nutrient foramen is present on its upper part.
– It is directed upwards.
– Nutrient artery is derived from anterior interosseous artery .
2) The medial surface :
– Lies between anterior and posterior border.
3) The posterior surface :
– It lies between Posterior and lateral border.
– It is subdivided into 3 areas by the 2 lines.
– It is divided into upper and lower parts by an oblique line .
– Lower part is further divided into medial and lateral area by a vertical line.
Lower end of ulna bone
– It is made up of head and styloid process.
– The head articulates with ulnar notch of radius and forms inferior radioulnar joint.
– It is separated from the wrist joint by articular disc .
– Ulnar artery and nerve lies on the anterior aspect of ulnar head.
– Styloid process projects downwards posteromedial side of lower end of Ulna.
– Posteriorly, between the head and styloid process , there is a groove for the extensor carpi ulnaris tendon.
• ATTACHMENTS
– Inserted into superior surface of olecraolecranon.
– Anterior part of this surface is covered by a bursa.
2) The Brachialis
– Inserted into anterior surface of Coronoid process including ulnar tuberosity
3) The Supinator
– Arises from supinator crest and from triangular area in front of the supinator crest.
4) Flexor digitorum superficialis ( ulnar head )
– Arises from tubercle at the upper end of medial margin of Coronoid process.
5) Pronator teres ( Ulnar head )
– Arises from Coronoid process ( medial margin ).
6) Flexor digitorum profundus
– Arises from,
√ Upper 3/4 th of anterior and medial surface of shaft.
√ The Coronoid and olecranon process ( medial surface )
√ Posterior border of shaft through an aponeurosis which also gives origin to flexor carpi ulnaris and extensor carpi ulnaris.
7) The Pronator quadratus
– Originates from oblique ridge on lower part of anterior surface.
8) Flexor carpi ulnaris ( ulnar head )
– Arises from medial side of olecranon process and from posterior border.
9) Extensor carpi ulnaris
– Arises from Posterior border.
10) The Anconeus
– Inserted into olecronon process ( lateral aspect ).
– And upper 1/4 th of shaft ( posterior surface).
11) The lateral part of posterior surface gives origin from above downwards to adductor pollicis longus, the extensor pollicis longus and the extensor indicis.
12) The interosseous membrane
– Attached to interosseous border.
13) The oblique cord
– Attached to ulnar tuberosity.
14) Capsular ligament of elbow joint
– Attached to margin of Trochlear notch
i.e., to the Coronoid and olecranon processes.
15) The annular ligament of superior radioulnar joint
– Attached to two margins of radial notch of ulna.
16) The ulnar collateral ligament of wrist
– Attached to styloid process.
17) The articular disc of inferior radioulnar joint
– Attached by its apex to small rough area just lateral to styloid process.
• OSSIFICATION OF ULNA BONE
* Primary centre
– The shaft and most of upper end ossifies from primary centre which appears during 8 th week of development.
* Secondary centre
– Superior part of olecranon process ossify from secondary centre .
– This appears during 10 th year.
– It forms a scale like epiphysis which joins the rest of bone by 16 th year.
– The lower end ossifies from a secondary centre appears during 5 th year and joins with shaft by 18 th year
– This is growing end of bone.
• CLINICAL ANATOMY
√ The ulna is a stabilising bone of forearm , with its Trochlear notch gripping the lower end of humerus.
On this foundation, the radius can pronate and supinate for efficient working of the upperlimb.
√ The shaft of ulna may fracture either alone or along with that of radius .
Cross union between radius and ulna must be prevented to preserve pronation and supination of hand.
√ Dislocation of elbow
– Produced by fall on outstretched hand with elbow slightly flexed.
– Olecranon shifts Posteriorly and elbow is flexed in slight flexion.
– Normally , in an extended elbow , the tip of the olecranon lies in a horizontal line with 2 epicondyles of the humerus and in the flexed elbow , the three bony points form an equilateral triangle .
These relations are disturbed in elbow dislocation.
√ Fracture of olecranon
– It is common and is caused by fall on point of elbow.
√ Fracture of Coronoid process
– It is uncommon and us usually accompanies with elbow dislocation.
√ Madelung’s deformity
-It is dorsal displacement of lower end of Ulna , due to growth retardation of the lower end of radius.
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