Bones - Ulna Flashcards
If the radius is the ‘pivot bone’, what is the ulna?
What type of bone is the ulna?
The stabilising bone.
It runs parallel to the radius and is a long bone is the forearm.
What are the important bony landmarks of the proximal ulna?
The ulna articulates with the trochlea of the humerus to enable movement of the elbow joint.
1) Olecranon - a large projection of the bone that extends proximally, forming part of the trochlear notch. It can be palpated as the ‘tip’ of the elbow. The triceps brachii muscle attaches to its superior surface.
2) Coronoid process - this ridge projects outwards anterioly, forming part of the trochlear notch.
3) Trochlear notch - formed by the olecranon and coronoid process. It is wrench shaped, and articulates with the trochlea of the humerus.
4) Radial notch - located on the lateral surface of the trochlear notch, this area articulates with the head of the radius.
5) Tuberosity of ulna - a roughening immediately distal to the coronoid process - this is where the brachialis muscle attaches.
What are the surfaces of the shaft of the ulna?
The ulnar shaft is triangular in shape, with three borders and three surfaces:
Three surfaces:
1) Anterior - site of attachment of the pronator quadratus muscle distally.
2) Posterior - site of attachment of many muscles.
3) Medial - unremarkable.
What are the borders of the ulna?
Posterior - palpable along the entire length of the forearm posteriorly.
Interosseous - site of attachment of the interosseous membrane, which spans the distance between the two forearms.
Anterior - unremarkable.
What are the features of the distal ulna?
Much smaller in diameter that the proximal end. It is mostly unremarkable, terminating in a rounded head, with distal projection - the ulnar styloid process.
The head articulates with the ulnar notch of the radius to form the distal radio-ulnar joint.
Clinical relevance - common fracture of the ulna
The forearm is a common site for bone fractures.
1) Fracture of the ulna alone - usually occurs as a result of the ulna being hit by an object. The shaft is most likely to fracture. Muscular tone will pull the proximal ulna posteriorly.
2) Fracture of the olecranon process - caused by patient falling on a flexed elbow. The triceps brachii can displace part of the fragment proximally.
The ulna and radius are attached by the interosseous membrance. The force of a trauma to one bone can be transmitted to the other via this membrane. Thus, fractures of both the forearm bones are not uncommon.
There are two classical fractures:
1) Monteggia’s fracture - usually caused by a forces behind the ulna. The proximal shaft of ulna is fracture and the radius dislocates anteriorly at the elbow.
2) Galeazzi’s fracture - a fracture to the distal radius, with the ulna head dislocating at the distal radio-ulnar joint.
