Ulna

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

1. Upper end 
2. Lower end 
3. Shaft 

1. Coronoid process 
2. Olecranon process 

It has two notches 

1. Trochlear notches 
2. Radial notches 

 

Olecranon process 

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.

 

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