Elbow

The elbow joint ( articulatio cubiti Latin, from Greek kýbiton κύβιτον, elbow ') is a composite joint ( articulatio composita ). It consists of three sub- functional joints with a common joint capsule in which the upper arm bone (humerus ) and the two forearm bones spoke ( radius) and ulna ( ulna ) will contact each other with one of the two bones. The forearm can be flexed at the elbow joint against the upper arm and stretched. In addition, the joint is functionally involved in the Umwendebewegungen hand, pronation and supination. This will be made ​​possible with a complex rotational movement of the spoke.

Partial joints

In the upper arm -Ellen - joint, the humerus role ( trochlea ) is related to the corresponding withholding at the Elle ( trochlear notch ) in conjunction. Functionally, it is a hinge joint, in which the forearm can be compared with the upper arm flexed or extended ( flexion and extension ).

The articular surfaces of the humeral -spoke joint are the humerus head ( capitellum ) and the glenoid fossa of the radius ( the radius articular fovea ). Of the joint surfaces starting, the upper-arm spokes - joint is a ball joint, but causes the connective tissue band adhesion between the two forearm bones ( interosseous membrane ) a fixation of the spoke at the Elle, so that the partial joint has only two degrees of freedom: flexion and extension as well as the rotational movement inwardly and outwardly ( supination and pronation ).

The proximal ( proximal ) Ellen -spoke joint is a pivot joint. The radius of the spokes joint surface ( articular circumferentia radii ) is related to the recovery of the spoke to the ulna ( radial notch of the ulna ) and located on the inside of the cartilaginous annular spoke tape ( annular ligament of the radius ) in conjunction.

Joint capsule

The three sub- joints of the elbow joint are spacious enclosed by a joint capsule and form a functional unit. The humerus, the capsule is mounted above the joint surfaces and surrounding the hole for the upper end of the ulna ( olecranon fossa ).

At the Elle the joint capsule is mounted very close to the transition between cartilage and bone. In addition there are attachments to the upper end of the ulna ( olecranon ) and crown projection ( coronoid process ). At the spoke, the capsule is wide and forms a small sac ( recess sacciformis ). It ranges up there in the neck region of the bone.

In extension of the forearm to the back sets, in flexion the front of the joint capsule in wrinkles. Formed in the joint body fat against each other caused by the movement of the bone spaces fill flexible. The capsule itself is protected move upward ( dorsal) by irradiating muscle fiber traits of the triceps brachii and ventral ( anterior ) of the musculus brachialis excited and before entrapment between the moving joint surfaces.

The joint capsule is the median nerve and ulnar nerve innervated by branches of the radial nerve, musculocutaneous nerve. In addition, smaller branches come from the surrounding muscles to the joint capsule.

Bursa

In the vicinity of the elbow joint located at places of dominance of mechanical stress individually variable pronounced bursa. They usually have no connection to the joint cavity. One example is the bursa between the upper end of the ulna and the skin ( olecranon bursa subcutanea ). His swelling is referred to horses as " Stoll bump ".

Bands

The elbow joint is guided by strong ligaments.

On the sides of the elbow joint is stabilized by side bands (including collateral ligaments ), which cross each other in their course.

• The Ellen - sideband ( ulnar collateral ligament ) extends from the top of the central Oberarmknorrens ( medial epicondyle of the humerus ) to the central side of the confiscation of the humerus to the ulna role.
• The spokes - sideband ( radial collateral ligament ) arises from the attachment of the lateral Oberarmknorrens ( lateral epicondyle of the humerus ) and radiates with its fibers into the annular spoke tape ( " annular ligament of the radius " ) a.

In addition, the elbow joint has still the annular spoke tape ( annular ligament of the radius, also called " ring band "). This is to be regarded as part of the joint capsule. It comprises of the ulna side coming, the spoke head (caput radii ) runs once around him and is functionally its attachment, however, allows the inner surface covered with cartilage, a free rotation of the spoke against the ulna.

Musculature

Active movements of the elbow joint are mainly caused by the upper arm muscles, although a part of the forearm muscles involved in the movements. Since the main degree of freedom of the elbow joint extension or flexion is, in principle, a distinction here between flexors ( flexor muscles ) and extensors ( extensors ). The flexors are on the front of the upper arm. They include the biceps brachii and the brachialis muscle. On the back of the upper arm of the triceps brachii and the anconeus musculus ensure that the forearm can be stretched or reduced.

Degrees of freedom

In the elbow joint flexion and extension of the forearm against the upper arm and the turning over of the forearm are possible. The ranges of motion following the specified start from the neutral position.

The flexion and extension take place in the upper arm joint and spoke in the upper arm -Ellen - joint. A diffraction up to 150 ° (angle between the forearm and upper arm ) are performed. A stretching ability of the neutral position is different for every person. In children and women can be a hyperextension of about 10 ° exist.

The inversion of the forearm is made possible by rotational movement of the spoke against the ulna. This rotation takes place in the proximal Ellen -spoke joint and correspondingly in the distal Ellen -spoke joint ( distal radioulnar joint ). Both movements are possible up to an angle of 80 ° to 90 °. In the upper arm there is hinge -spoke likewise to a rotational movement.

Diseases

In case of failure of the joint stress it can lead to so-called tennis elbow ( epicondylitis ) or Ulnarisrinnen syndrome come. Due to infections, joint inflammation (arthritis) can occur.

The elbow dysplasia is a more common developmental disorder of the elbow joint in young animals großwüchsiger breeds.

Injuries

The elbow joint is exposed in sports and games and physical work high loads. Already in early childhood fractures and dislocations are common in overload. Depending on the location of the fractures on the bones involved in the elbow joint are called: supracondyläre humeral fractures, Epicondylusabrisse at the distal humerus, olecranon fractures ( Olecranonfrakturen ) and radial head fractures. There are also combinations of these injuries, especially combined lesions of the proximal forearm. Since it often is considerably shifted periarticular fractures, a surgical procedure is indicated.

Ellenbogenluxationen are under the shoulder dislocations the most common dislocations of large joints, often associated with tears of the lateral ligaments and resulting instabilities as well as bone fractures, such as radial head fractures or Epicondylusabrisse.

Fractures near the elbow joint are both in children and adults is relatively common, such as the distal humeral fracture, the radial head fracture and olecranon fracture. Since the fractures usually are caused by falls, where considerable forces acting on the elbow joint, are also frequently comminuted fractures. Since it is joint fractures, operative measures here are almost always appears to restore the anatomic joint surfaces. In childhood, there is also the great danger of the violation of the growth plates.

Literature and sources

• W. Platzer: Pocket Atlas of Anatomy, Volume 1, Thieme Verlag
• F.-V. Salomon: anatomy for veterinary medicine, Enke, Stuttgart, 2004, pp. 110-147, ISBN 3-8304-1007-7