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What is Ulna?

MVSAT 2024

The ulna is a long bone that is found in the forearm. It starts from the elbow and then stretches to the smallest finger in the hand. Ulna runs parallel to the radius. The ulna is thinner and slightly longer than the radius bone. But because the radius is thicker in nature than the ulna, the radius is considered longer than the ulna.


Ulna Anatomy

The ulna is a long bone in the forearm that runs from the elbow to the smallest finger and is located on the medial side of the forearm. Close to the elbow, the ulna is wider and then narrows as it approaches the wrist. The ulna has a bony process called the olecranon process that is located just below the elbow. The olecranon process is a hook-like structure on the humerus that fits into the olecranon fossa. The trochlea of the humerus forms a hinge joint with this, preventing hyperextension.


Structure of Ulna

  • Olecranon process and coronoid process are the two processes that are present in Ulna. They are present close to the elbow.

  • The olecranon process is a hook-like structure. This structure fits in the olecranon fossa that is present in the humerus.

  • From the anterior portion of the ulna, the coronoid process bulges out. It is triangular in shape. It helps in stabilizing the elbow joint. This further helps in preventing hyperflexion.

  • With the help of the olecranon and coronoid process, a semilunar notch is formed. It is a large depression and helps in the articulation of the trochlea of the humerus.

  • The upper part of the ulna is prismatic in shape. The central part is straight and the lower part is rounded.


Function of Ulna

  • The ulna contributes to the formation of the wrist and elbow joints. In a hinge joint, the ulna articulates with the humerus at its most proximal point, forming the elbow. The trochlea of the humerus is found to sit with the semi-lunar notch of the ulna to form a joint.

  • Pronation (from the proximal joint) and supination (from the distal joint) of the forearm are caused by the ulna articulating with the radius proximally and distally.

  • The interosseous membrane of the ulna articulates with the radius in a syndesmosis joint. A syndesmosis joint is formed when two adjacent bones are linked together by strong ligaments.


Fractured Ulna

The fractures of ulna occur due to fragility and falling from high ground on the hand. The different types of fractures of the ulna are listed below:

  • Monteggia fracture: In this fracture, the ulnar shaft and the radial head are involved. These two structures are dislocated from their places.

  • Hume fracture: This fracture involves the dislocation of the radial head and the fracture of the olecranon process.

  • Galeazzi's fracture: This fracture occurs when the distal radius gets fractured and this results in the dislocation of the ulnar head.


Conclusion

The ulna is found in the forearm and it is one of the long bones. It starts from the elbow and then stretches to the smallest finger. The radius is slightly smaller than the Ulna but the radius is thicker than Ulna. The elbow and wrist joints are formed by the Ulna. It also helps in forming the elbow. There are different types of fractures that can occur in the ulna and thus care should be taken.

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FAQs on Ulna

1. What is proximal ulna?

The structure of the proximal ulna is hook-like. It helps in articulating with the trochlea of the humerus. This further helps in creating a hinge joint that is present in the elbow. With the help of the olecranon and coronoid process, this articulation is formed. 

2. Where is the head of the ulna?

The head of the ulna is located at the anterior and distal end. The ulnar notch of the radius is connected to the triangular articular disc of the wrist joint with the help of this head. 

3. What is a distal ulna fracture? 

This fracture occurs along the length of the ulna bone. It is also known as isolated ulnar shaft fracture. This fracture can take approximately 3-6 months to heal. In this fracture, the ulna is broken or dislocated from the wrist side. Though it is a very rare type of fracture still can be very painful. Pain and swelling in the forearm are seen in this fracture. Usually occurs to the children involved in sports. 

Q4:What is a Distal Ulna Fracture

Ans: The distal ulna fractures are very rare. They're frequently discovered in association with distal radius fractures, and the distal ulna's interplay with the radioulnar joint and triangular fibrocartilage complex makes distal ulna fractures difficult to explain and treat. Fixation of distal ulna fractures might be difficult due to comminution, which makes reduction difficult. Because of the thin soft tissue, hardware prominence might occur, necessitating implant removal.

Q5: What is Caput Ulnae Syndrome ?

Ans: A caput ulnae syndrome arises when the joints of the head of the ulna lose their rigidity due to trauma or persistent inflammation.

Q6: What is an Ulna Fracture or the Left Ulna Fracture?

Ans: A break in the ulna bone, one of the two bones of the forearm, which can be either the left ulna bone or the right ulna bone is known as an ulna fracture. It is frequently linked with a radius fracture, the other forearm bone.


An ulna fracture can be a single break, as in a so-called nightstick fracture, which occurs when someone is stuck on the inside of the forearm with a stick, especially when putting their arm up to protect their head from damage.


Falling on the forearm or on an outstretched arm can potentially cause the ulna bone to shatter.


Ulna fractures are more likely in men before the age of 40 and in women beyond the age of 60. Adolescents that participate in athletics are at an increased risk.

Q7: What is a Radio Ulna Bone?

Ans: The radio ulna is a single bone that is present in the forelimbs of an amphibian such as a frog. The radio ulna bone represents the unique fusion of the separate radius and the ulna of the higher vertebrate forms.


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