Ulna

Os ulnae

The ulna is the longer forearm bone with a prominent olecranon process at its proximal end. The trochlear notch articulates with the trochlea of the humerus. The coronoid process prevents posterior dislocation. The head and styloid process are at the distal end.

Тип Bone
Система органов Skeletal
Область тела Forearm
Родительская структура forelimb zeugopod bone
Латинское название Os ulnae
FMA ID 23466

Функция

The medial bone of the forearm forming the primary articulation at the elbow. Provides stability during forearm rotation and serves as the axis around which the radius rotates.

Клиническое значение

Olecranon fractures result from direct falls on the elbow. Monteggia fractures involve ulnar shaft fracture with radial head dislocation. The ulnar nerve passes posterior to the medial epicondyle, vulnerable to compression.

Часто задаваемые вопросы

What is the primary function of the ulna at the elbow?
The ulna forms the primary articulation at the elbow joint. Its olecranon (the bony point of the elbow) fits into the olecranon fossa of the humerus during extension, and its trochlear notch articulates with the trochlea of the humerus throughout the range of elbow flexion and extension. This hinge-like articulation makes the elbow joint inherently stable, with the ulna providing the structural framework for elbow movement.
What is the role of the ulna in forearm rotation?
During forearm rotation (pronation and supination), the ulna remains relatively stationary while the radius rotates around it. The radius, connected to the ulna at the proximal and distal radioulnar joints, swings in an arc when the forearm pronates or supinates, while the ulna serves as the fixed axis of rotation. This is why the ulna is considered the axis bone of the forearm.
What is an olecranon fracture and how does it typically occur?
An olecranon fracture is a break through the bony process at the proximal end of the ulna that forms the point of the elbow. It most commonly results from a direct fall onto a flexed elbow or from a direct blow. Because the triceps muscle inserts on the olecranon, it often displaces the proximal fragment proximally. Most displaced olecranon fractures require surgical fixation with tension band wiring or plate fixation to restore active elbow extension.
What is a Monteggia fracture and why is it important to recognize?
A Monteggia fracture is a combined injury involving a fracture of the proximal ulnar shaft with an associated dislocation of the radial head at the proximal radioulnar joint. It is important to recognize because the radial head dislocation can be missed on plain radiographs if the entire forearm is not imaged. Failure to reduce the radial head dislocation leads to chronic pain, loss of forearm rotation, and ultimately degenerative joint disease.
Where does the ulnar nerve pass relative to the ulna, and why is it vulnerable there?
The ulnar nerve passes through a groove posterior to the medial epicondyle of the humerus—near the proximal ulna—in the cubital tunnel. This superficial location makes it vulnerable to compression from leaning on the elbow, from stretching during prolonged elbow flexion, or from osteophytes and scar tissue in the tunnel. Compression at this site is cubital tunnel syndrome, the second most common peripheral nerve entrapment after carpal tunnel syndrome.

Связанные структуры

articulation joint nutrient foramen conduit outer fibrous layer of periosteum capsular layer of periosteum periosteum pre-cartilage condensation pre-chondrogenic condensation postcranial axial skeleton axial skeleton radial element actinost cavity of bone organ bone organ cavity

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Data sources: Terminologia Anatomica, Foundational Model of Anatomy, Wikidata.