The elbow joint , also known as elbow joint , ( Latin Articulatio cubiti , from ancient Greek κύβιτον kýbiton , German 'elbow' ) is a compound joint ( Articulatio composita ). It is functionally comprised of three sub-joints with a common joint capsule in which the upper arm bone ( humerus ) and the two forearm bones spoke ( radius ) and ulna ( ulna ) occurs in each case with one of the other two bones in connection. The forearm can be bent and stretched at the elbow joint in relation to the upper arm. In addition, the joint is functionally involved in the turning movements of the hand, pronation and supination . This is made possible, among other things, by a complex rotating movement of the spoke.
- Upper arm- ulnar joint ( articulatio humeroulnaris )
In the upper arm-ulnar joint, the humerus roll ( trochlea humeri ) is connected to the associated retraction at the ulna ( incisura trochlearis ). Functionally, it is a hinge joint in which the forearm can be bent or stretched in relation to the upper arm ( flexion and extension ).
- Upper arm-spoke joint ( articulatio humeroradialis )
The articular surfaces of the upper arm-spoke joint are the humerus head ( capitulum humeri ) and the joint pit of the spoke ( fovea articularis radii ). Starting from the joint surfaces, the upper arm-spoke joint is a ball- and- socket joint , but the connective tissue ligament between the two forearm bones ( membrana interossea antebrachii ) fixes the spoke to the ulna, so that the partial joint has only two degrees of freedom : flexion and extension as well the inward and outward rotation ( supination and pronation ).
- Proximal ulnar-spoke joint ( articulatio radioulnaris proximalis )
The proximal elbow joint is a pivot joint . The circumference of the radial articular surface ( circumferentia articularis radii ) is connected to the retraction for the spoke at the ulna ( incisura radialis ulnae ) and the cartilaginous ring-shaped radial ligament ( ligamentum annulare radii ) on the inside .
The three partial joints of the elbow joint are extensively enclosed by a joint capsule and form a functional unit. The capsule is attached to the humerus above the joint surfaces and encloses the pit for the upper end of the ulna ( fossa olecrani ).
The joint capsule is attached to the ulna very close to the transition between cartilage and bone . In addition, there are attachments at the upper end of the ulna ( olecranon ) and the coronoid process . At the spoke, the capsule is large and forms a small bulge ( recessus sacciformis ). There it extends into the neck area of the bone.
The back of the joint capsule folds when the forearm is stretched and the front of the joint capsule when bent. Fat bodies formed in the joint flexibly fill the spaces created by the movement of the bones against each other. The capsule itself is stretched backwards ( dorsally ) by irradiating muscle fibers from the triceps brachii muscle and ventrally ( ventrally ) by the brachialis muscle and is protected from being trapped between the movable joint surfaces.
The joint capsule is innervated by branches of the radial nerve , musculocutaneous nerve , median nerve, and ulnar nerve . In addition, smaller branches from the surrounding muscles reach the joint capsule.
In the vicinity of the elbow joint, there are individually variable bursa at points of increased mechanical stress . As a rule, they have no connection to the joint cavity. One example is the bursa between the upper end of the ulna and the skin ( bursa subcutanea olecrani ). In horses, its swelling is known as a "stud bump".
The elbow joint is guided by strong ligaments .
The elbow joint is stabilized on the sides by side ligaments (also called collateral ligaments), which cross each other in their course.
- The ulnar collateral ligament ( Ligamentum collaterale ulnare ) extends from the attachment of the central humerus ( epicondylus medialis humeri ) to the central side of the indentation for the humerus roll at the ulnar .
- The radial collateral ligament ( Ligamentum collaterale radiale ) arises from the attachment of the lateral humerus ( Epicondylus lateralis humeri ) and radiates with its fibers into the annular radial ligament ( Ligamentum annulare radii ).
In addition, the elbow joint has the ring-shaped spoke ligament ( ligamentum annulare radii , also called "ring ligament" for short). This is to be regarded as part of the joint capsule. Coming from the ulnar side, it encompasses the head of the spoke ( caput radii ), runs around it and functionally serves to secure it, but allows the radius to rotate freely in relation to the ulna thanks to the cartilage-covered inner surface.
Active movements in the elbow joint are mainly caused by the upper arm muscles, although some of the forearm muscles are also involved in the movements. Since the main degree of freedom of the elbow joint is stretching or flexion, is here in principle between flexors ( flexors () and extensors extensors ) distinguished. The flexors are on the front of the upper arm. They include the biceps brachii and the brachialis muscles . On the back of the upper arm, the triceps brachii and anconeus muscles ensure that the forearm can be stretched or lowered.
Degrees of freedom
In the elbow joint, the forearm can be bent and extended in relation to the upper arm and the forearm can be turned over. The neutral position (0 °) is considered to be an extended elbow, with the forearm in the middle between supination and pronation so that the thumb points forward. The following ranges of motion are based on this neutral position:
- Flexion and extension
The flexion and extension take place in the upper arm-spoke joint and in the upper arm-ulnar joint. A flexion can be performed up to 150 ° (angle between forearm and upper arm). The ability to stretch beyond the neutral position is not given to everyone. Children and women can have hyperextension of about 10 °.
- Turning the forearm over
The turning over of the lower arm is made possible by the rotary movement of the spoke relative to the ulna. This rotational movement takes place in the elbow-spoke joint close to the body and accordingly also in the distal-elbow joint ( articulatio radioulnaris distalis ). Both movements are possible up to an angle of 80 to 90 °. There is also a rotary movement in the upper arm-spoke joint.
The elbow joint is exposed to high stresses during sport and play and during physical work. Even in early childhood, bone fractures and dislocations are common when overstrained. Depending on the localization, the fractures are referred to according to the bones involved in the elbow joint as: supracondylar upper arm fractures, epicondyle avulsion on the distal upper arm, elbow hook fractures (olecranon fractures ) and fractures of the radial head . There are also combinations of these injuries, particularly combined lesions of the proximal forearm. Since the fractures near the joint are often significantly displaced, an operative approach is indicated.
After shoulder dislocations, elbow dislocations are the most common dislocations of large joints, often associated with ruptures of the collateral ligaments and the resulting instabilities, as well as with bone fractures such as fractures of the radial head or epicondyle avulsion.
Bone fractures near the elbow joint are relatively common in both children and adults, such as the distal humerus fracture , the radial head fracture, and the olecranon fracture . Since the fractures are usually the result of falls in which considerable forces act on the elbow joint, debris fractures are also found more frequently . Since joint fractures are involved, surgical measures are almost always indicated in order to anatomically restore the joint surfaces. In childhood there is also a great risk of damaging the growth plates .
Literature and Sources
- Werner Platzer, Helmut Leonhardt, Werner Kahle: Pocket Atlas of Anatomy. Volume 1, Thieme Verlag 1991, ISBN 3-13-552406-X .
- F.-V. Salomon: anatomy for veterinary medicine. Enke, Stuttgart 2004, ISBN 3-8304-1007-7 , pp. 110-147.
- Carsten Stasnyk, Hagen Gasse: On the innervation of the joint capsules in dogs. Part 2: elbow joint. In: Small Animal Practice. 44: 501-506 (1999).