Comprehensive Anatomy and Clinical Insights of the Ulna Bone

 

ULNA

The forearm's medial bone, the ulna, is homologous to the lower limb's fibula. Its bottom end is small and rounded, while its higher end has two processes: a shaft.

Determination of the Side

1. The upper end has a forward-facing concavity and resembles a hook.
2. The shaft's lateral edge is angular and crest-like.
3. The lower end of the ulna's rounded head is posteromedial to the pointed styloid process. 

Features

Upper End

1. The trochlear and radial notches, as well as the olecranon and coronoid processes, are visible on the top end.
2. From the shaft, the olecranon process protrudes upward. Its surfaces are medial, lateral, anterior, posterior, and superior.
3. The posterior surface creates a triangular subcutaneous area that is divided from the skin by a bursa; the anterior surface is articular and forms the top portion of the trochlear notch. It is contiguous with the posterior margin of the ulna's shaft inferiorly.
4. The medial surface is connected inferiorly with the medial surface of the shaft; its upper portion forms the elbow's tip. The posterior side of the shaft is continued on the smooth lateral surface.There is a roughened patch on its posterior superior surface.
   
5. The coronoid process, which has four surfaces—superior, anterior, medial, and lateralprotrudes forward from the shaft immediately below the olecranon process. The term coronoid means "crow's beak" in Greek.
6. The anterior surface is rough and triangular in shape; the superior surface forms the bottom portion of the trochlear notch. 
7. Its inferior corner creates the ulnar tuberosity.
8. The radial notch for the radius head denotes the upper portion of its lateral surface. Attached to the notch's anterior and posterior edges is the annular ligament. 
9. To make room for the radial tuberosity, the lower portion of the lateral surface forms a depressed area. The supinator crest, a ridge, limits it from behind.The medial surface and the shaft's medial surface are connected.
10. To form the elbow joint, the trochlear notch forms an articular surface that articulates with the trochlea of the humerus.
11. The superior radioulnar joint is formed by the articulation of the radial notch with the radius head.

Shaft

The shaft has three borders and three surfaces

Borders

1. The middle two-fourths of the interosseous or lateral border have the sharpest edge. It reaches the lateral side of the head inferiorly. It is connected with the supinator crest superiorly.
2. There is a large, rounded border in front. It starts above on the medial side of the ulnar tuberosity, travels through its lower third and ends at the styloid process' medial side.
3. The back border is beneath the skin. It starts above at the base of the styloid process and ends at the apex of the triangular subcutaneous area behind the olecranon process.

Surfaces

1. Between the anterior and interosseous borders is the anterior surface. On the upper portion of this surface is visible a nutrient foramen. It is aimed upward.
2. The anterior interosseous artery gives rise to the nutritional artery.
3. The anterior and posterior margins separate the medial surface.
4. The interosseous and posterior borders are where the posterior surface is located. Two lines split it into three sections. It is divided into upper and lower portions by an oblique line. A vertical line further splits the lower portion into a medial and lateral section.

Lower End

1. The styloid process and the head comprise the bottom end. The inferior radioulnar joint is formed by the head's articulation with the radius's ulnar notch.
2. The articular disc divides it from the wrist joint.
3. On the front aspect of the ulnar head are the ulnar artery and nerve. The lower end of the ulna's posteromedial side is where the styloid process projects downward. 
4. The tendon of the extensor carpi ulnaris is located in a groove posteriorly, between the styloid process and head.

Attachments

1. The triceps brachii are placed into the ridged area on the back of the olecranon process' superior surface. A bursa covers the anterior portion of the surface.
2. The brachialis is inserted into the ulnar tuberosity and the anterior surface of the coronoid process.
3. The triangle region in front of the crest and the supinator crest are the sources of the supinator.
4. A tubercle at the upper end of the coronoid process' medial edge gives birth to the ulnar head of the flexor digitorum superficialis.
5. The medial border of the coronoid process gives rise to the ulnar head of the pronator teres.
6. The upper three-fourths of the anterior and medial surfaces of the shaft are the source of the flexor digitorum profundus, or deep in Latin.
7. The coronoid and olecranon processes' medial surfaces.
8. The posterior shaft border via an aponeurosis, which also serves as the origin of the flexor and extensor carpi ulnaris.
9. The oblique ridge on the inferior aspect of the anterior surface is the source of the pronator quadratus.
10. The posterior border and medial side of the olecranon process give rise to the flexor carpi ulnaris, or ulnar head.
11. The posterior border is where the extensor carpi ulnaris originates.
12. The upper quarter of the posterior portion of the shaft and the lateral aspect of the olecranon process are where the anconeus is inserted.
13. The abductor pollicis longus, extensor pollicis longus, and extensor indicis all have their origins in the lateral portion of the posterior surface, which is located downward from above.
14. The interosseous border is where the interosseous membrane is fastened.
15. The ulnar tuberosity is where the oblique cord is attached.
16. The coronoid and olecranon processes, or the edges of the trochlear notch, are where the elbow joint's capsular ligament is joined.
17. The two edges of the radial notch of the ulna are where the superior radioulnar joint's annular ligament is joined.
18. The styloid process is connected to the wrist's ulnar collateral ligament.
19. Situated directly lateral to the styloid process, the articular disc of the inferior radioulnar joint is linked at its apex to a little rough region.

Ossification

During the eighth week of development, a major center emerges, from which the shaft and most of the upper end of the ulna ossify. The olecranon process' superior portion osseifies from a secondary center that emerges in the tenth year. By the sixteenth year, it creates a scale-like epiphysis that links the remainder of the bone. By the 18th year, the lower end has joined the shaft after ossifying from a secondary center that first develops in the fifth year. This is the bone's developing end.

MEDICAL ANATOMY

With its trochlear notch holding onto the lower end of the humerus, the ulna serves as the forearm's supporting bone. For the upper limb to function efficiently, the radius can pronate and supinate on this basis. The ulna shaft may break on its own or in conjunction with the radius shaft. To maintain the hand's pronation and supination, the cross-union of the radius and ulna must be avoided. An elbow dislocation results by falling on an outstretched hand with the elbow slightly bent. The elbow is fixed in a mild flexion, and the olecranon process shifts posteriorly. The olecranon process tip normally forms a horizontal line with the humerus's two epicondyles when the elbow is extended, and an equilateral triangle is formed by the three bony points when the elbow is flexed. When the elbow dislocates, these relationships are upset.

Falls on the elbow's point frequently result in olecranon process fractures. Rarely, an elbow dislocation is accompanied by a fracture of the coronoid process.
Due to delayed growth of the lower end of the radius, Madelung's deformity is dorsal subluxation (displacement) of the lower end of the ulna.