Ulna

Ulna


• It is the medial bone of the forearm & radius lie laterally.
• It is homologous to the fibula.

Parts of ulna  
  1. Upper end 
  2. Lower end 
  3. Shaft 

Upper end

 
• It is expended and hook-like whose concavity lies forward.
• The concavity is called trochlear notch which lies between the large olecranon process above and the small coronoid process below.

It has two processes:
  1. Coronoid process 
  2. Olecranon process 

It has two notches 

  1. Trochlear notches 
  2. Radial notches 

 

Olecranon process 

• It is directed forward.
• It has five surfaces 
Upper surface 
Rough posterior 2/3rd
• Gives insertion to the Triceps brachii

Anterior margin of this surface
• Gives attachment to the capsular ligament of the elbow joint.

Note:
Synovial bursa lies between the triceps brachii and capsular ligament of elbow joints.
Anterior surface 
It is smooth and forms the upper part of the trochlear notch.
Posterior surface 
It is subcutaneous 
Medial surface
Its upper part provides attachment to three structure 

• Origin of the ulnar head of the flexor carpi ulnaris
• Posterior band of ulnar collateral ligament 
Oblique band of ulnar collateral ligament

Lateral surface 
It is smooth.
 

Coronoid process 

• Lies below the olecranon process.
• It is a bracket-like projection.

• It has four surfaces 

Superior surface 
• It forms the lower part of the trochlear surface.
Anterior surface 
• It is triangular in shape.
• A tuberosity is present in the lower corner of this surface called ulnar tuberosity.

• Ulnar tuberosity→Gives insertion to the brachialis muscle.

Medial margin of this surface
• Provides attachment to the following muscle 

1. Anterior band of the ulnar collateral ligament 
2. Oblique band of ulnar collateral ligament.
3. Humero-ulnar head of the flexor digitorum-superficialis 
4. Ulnar head of pronator teres.
5. Ulnar head of the flexor policies longus.
Medial surface 
• Gives origin to the flexor digitorum profundus.
Lateral surface 
• Radial notch is present on this surface.
• Radial notch provides articulation to the head of the radius.
• A small fossa called supinator fossa present below the radial notch.
• Near the supinator fossa supinator crest is present.

Supinator crest
• Gives origin to the supinator muscle.

 

Shaft

It has three borders
  1. Lateral 
  2. Anterior 
  3. Posterior 
It has three surfaces 
  1. Anterior 
  2. Medial 
  3. Posterior 

Borders of Shaft:

Lateral border 
• It is the sharp among all three borders.
• It is continuous with the supinator crest.

• Give attachment to the interosseous membrane except its upper part.
Anterior border 
• It begins from the medial side of the ulnar tuberosity up to the base of the styloid process.

Upper 3/4th part
• Gives origin to the flexor digitorum profundus.
Posterior border
• It begins from the apex of the triangular area of the olecranon process and descends up to the styloid process.

Give attachment of three common aponeurosis 
1. Flexor digitorum profundus 
2. Flexor carpi ulnaris 
3. Extensor carpi ulnaris 


Surfaces of Shaft

Anterior surface
• Lies between the anterior and interosseous borders.
• Nutrient foramen present on this surface which is directed upward.

Upper 3/4th part
• Gives origin to the flexor digitorum profundus 

Lower 1/4th part
• Gives origin to the pronator quadratus
Medial surface 
Lies between the anterior and posterior border.

Upper 2/3rd of this surface
• Gives origin to the flexor digitorum profundus 
Posterior surface 
• Lies between the posterior and interosseous borders.
• It is divided into two parts smaller upper part and lower larger part by an oblique line.

Area above the oblique line
• Gives insertion to the anconeus muscle


• Again vertical line divides the lower larger area (below the oblique line) into two parts i.e
- Larger medial &
- Smaller lateral parts

Lateral parts gives attachment to three muscles from proximal to distal.
  1. Abductor pollicis longus in the upper 1/4th 
  2. Extensor pollicis longus in the middle 1/4th
  3. Extensor indicis in the next 1/4th 


Lower end

Its has two parts 
  1. Head 
  2. Styloid process 
Head 
• Its lateral part is articulate with the ulnar notch of radius to form the inferior radio-ulnar joint.
• Its inferior surface is smooth which is separated from the wrist joint by the articular disc.
Articular Disc
• Fibrocartilagenous Structure
• Due to its presence, Ulnar doesn't take part in the formation of wrist joint
• Wrist Joint is also called Radio-carpal Joint
Styloid process 
• It lies on the posteromedial aspect of the head of the ulna.
• Its tip provides attachment to the medial collateral ligament of the wrist joint.
• The tendon of the extensor carpi ulnaris lies in the groove between the back of the head of the ulna and the styloid process.