Ulna
The ulna ( Latin - anat. For ulna ) is one of the two bones of the forearm , along with the radius (spoke) . The ulna is located on the little finger side, less strong than the spoke and a typical long bone .
The adjective ulnar means "belonging to the ulnar " or as a directional indication "towards the ulnar ".
Top end
The ( proximal ) end of the ulna ( olecranon from ancient Greek ὠλένη = ulna κράνος = helmet ) located to the middle of the body is clearly thickened and ends in a broad, beak-like bone spur called the elbow hump ( tuber olecrani ). Its rear ( posterior ) surface is roughly triangular, smooth and is covered by a bursa ( bursa subcutanea olecrani ) because it lies directly under the skin. At the front edge of the bone spur you can see a transverse depression that serves as a base for the posterior fibers of the joint capsule of the elbow joint . The upper ( superior ) surface of the bone spur is roughly diamond-shaped and roughened where the tendon of the powerful three-headed upper arm muscle ( triceps brachii muscle ) radiates into the bone. The hook shape projecting to the bone spur forward elbow extension ( Processus anconeus ) engages in extension of the elbow joint ( articulatio cubiti ) in the bone spur pit ( olecranon fossa ) of the upper arm bone ( humerus ). The elbow head ( caput ulnare ) of the elbow-sided hand flexor ( muscle flexor carpi ulnaris ) arises at the medial edge of the bone spur directed towards the center . The elbow muscle ( Musculus anconaeus ) attaches to the side ( lateral ) edge . The front ( anterior ) surface of the bone spur is smooth, curved inward and covered by the articular cartilage. It forms the upper part of the joint surface, a notch for the joint role ( incisura trochlearis ), which is involved in the formation of the elbow joint. At the base of the bone spur, a lateral and central coronoid process ( lateral and medial coronoid processes ) encompass the head of the spoke.
For large breeds , it may, at the elbow dysplasia to broken bones ( fractures of the elbow extension or centripetal Kronfortsatzes come).
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The middle section of the ulna is called the ulnar body or corpus ulnae .
The ulna and the spoke form a functional unit on the forearm. This makes, among other anatomically is noticeable that both bones are coupled together in different ways. On the one hand, they each have an articulated connection to each other at their ( distal ) end, which is directed towards the middle of the body and remote from the middle of the body, and on the other hand, a fairly stable bond between the two spans almost the entire length ( membrana interossea antebrachii ). This relatively tight pull creates an edge ( margo interosseus ) on the ulna on the side facing the spoke . This represents the only sharp edge and is therefore easily palpable through the skin and is opposite the edge of the spoke of the same name.
A margin can also be defined on the front and back of the ulna ( margin anterior and posterior ).
Despite its almost cylindrical body, you can demarcate different areas on the ulna due to the edges just described. The front surface ( Facies anterior ) is the bone surface located between the front edge and the edge between the two forearm bones. There is also a surface between the front and rear edges, which is referred to as the surface facing the middle ( Facies medialis ). The rear surface ( Facies posterior ) is the surface that is spanned by the rear edge and edge between the two bones. This serves as the surface of the ligament between the two bones .
Lower end
The slightly widened lower end of the ulna is referred to as the ulna head ( caput ulnae ) and ends with the stylus extension ( processus styloideus ulnae ). This protrudes more or less clearly on the little finger side above the wrist. The circumferential circumferential surface of the articular surface ( circumferentia articularis ) located on the anterior side is connected to the notch ( incisura ulnaris ) for the head of the elbow on the spoke and the radial ligament of the radius ( ligamentum annulare radii ) covered with cartilage on the inside .
Adjacent joints
The ulna has no direct involvement in the articulated connection of the forearm bones with the carpal bones ( ossa carpi ). It has to bridge the distance with a joint disk ( discus articularis ) due to the joint end being further away from the center of the body .
The ulna and radius have two articulated connections. On the one hand there is the radial elbow joint ( articulatio radioulnaris proximalis ), which is sometimes included in the elbow joint ( articulatio cubiti ), and on the other hand the distal radial elbow joint ( articulatio radioulnaris distalis ). These enable the forearm, angled forwards, to turn around inwards and outwards of the radius around the ulna ( pronation and supination ). Thanks to the bends in both bones, the inward and outward twisting extends around 180 ° in total. This movement can be observed in isolation on the angled upper arm when the thumb side of the hand turns with the spoke from the inside to the top and outwards.
In animals that mainly run (e.g. horses , ruminants ), the ulna is bony with the spoke ( synostosis ) and the two bones are therefore immobile against each other.
See also
- Olecranon fracture
- Premature ulnar joint closure
- Monteggia fracture (fracture of the proximal ulnar shaft with dislocation of the radial head)
- Galeazzi fracture (fracture of the distal radial shaft with dislocation of the ulnar head)
