Synonyms: elbow dislocation, elbow dislocation, elbow dislocationAn elbow dislocation is a complete displacement of the parts involved in the elbow joint. This includes the sliding of the articular surface of the humerus out of its hinge-like enclosure by the ulna and the loss of contact between the head of the radius and the humerus.
Anatomy
Three bones meet in the elbow joint (Articulatio cubiti): The humerus, ulna and radius. They form 3 different joints, which together form a so-called hinge joint (trochoglymus). The humerus has a rounded joint surface, which is surrounded by the ulna with two bone processes like a hinge (hinge joint).
These processes are the upper end of the ulna (olecranon), which can be palpated as the “elbow bone”, and the crown process (proc. coronoidus) at the front. The head of the radius (Caput radii) is surrounded by a spherical joint surface.
This forms a lateral swivel joint with the ulna, which is stabilized by a circular ligament (Ligamentum anulare radii) running around the spoke head. At the top, the spoke head forms a ball joint with the articular surface of the humerus. The lateral movements of this ball-and-socket joint are restricted on both sides by collateral ligaments between the humerus and the radius or ulna (ligamentum collaterale radii or ulnae).
The joint capsule is relatively wide and includes the joint forming parts. Muscles and the collateral ligaments start there and additionally stabilize the joint. A healthy joint allows outward (pronation) and inward (supination) rotation of the forearm and flexion of approximately 140°. A further extension beyond the resting position is not possible due to the bony structures (except for women and children, sometimes 5-10°). A lateral bending of the forearm is also not possible with intact ligaments.
Origin
The elbow dislocation can rarely be congenital, but in almost all cases it is caused by external force. The most common mechanism is falling on the stretched arm, often this situation occurs during sports. Direct influences on the arm can also be causal if they result in overstretching or excessive angulation of the elbow joint.
Corresponding to the high percentage of falls on the stretched arm, there is a dorsal (backward) dislocation in approx. 80-90% of cases: Due to the violent impact from the front, the upper end of the ulna (olecranon) becomes a pivot point and lifts the humerus out of its joint fossa. As a result, the humerus is located in front of the actual joint.
However, the ulna and radius are located behind the humerus, which is decisive for classification as a dorsal dislocation. In less than 10% of cases, a sole (isolated) dislocation of the spoke head from its position occurs. In even fewer cases, the ulna and spoke are located after dislocation in front of (ventral) or beside the humerus or are located separately on either side (diverging).
The elbow dislocation always results in a rupture of the capsule. In addition, in many cases, damage to the ligamentous apparatus occurs, e.g. torn ligaments at the elbow. In about 20% of the cases, dislocation is accompanied by bony injuries. These can be the fracture of the spoke head, the rupture of the crown process or the upper end of the ulna (olecranon) or ruptures of the humerus. Also injuries of the conducting pathways (arteries, veins, nerves) occur, because they run in close proximity to the elbow joint.