An 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 of elbow dislocation
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.
The humerus has a rounded joint surface, which is surrounded by the ulna with two bone processes like a hinge (hinge joint). These extensions are the upper end of the ulna (olecranon), which can be palpated as “elbow bone” at the back, and the crown process at the front.
The head of the radius 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 joint surface of the humerus.
However, the lateral movements of this ball joint are restricted on both sides by collateral ligaments between the humerus and the radius or ulna.
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.
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The elbow dislocation can rarely be congenital, but in almost all cases, it is caused by an 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 proportion 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 situated 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. Besides, in many cases, there is damage to the ligamentous apparatus, for example, 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. There are also injuries to the conduction pathways (arteries, veins, nerves), as these run near the elbow joint.
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Therapy of elbow dislocation
In general, the joint should be repositioned as soon as possible, preferably within 6 hours. Otherwise, there is a risk of vascular or nerve damage due to the proximity.
In the case of a dislocation without accompanying bony injuries, the aim is to reposition the joint and restore normal joint conditions. For this purpose, the joint surface of the humerus must snap back into the joint cavity of the ulna. This is usually carried out under general anesthesia, as with regional anesthesia, the feeling and the ability to move are still restricted for a longer period, which can be dangerous.
In the case of a dorsal dislocation, with the upper arm fixed, a pull is applied to the forearm, which is bent by approx. 30° and turned outwards, and this is then flexed up to 90°. In the case of a ventral dislocation, an attempt is made to lock the forearm down again when it is bent. After reduction, the joint must be checked by x-ray.
If ligament damage is suspected, the success of the reduction and the extent of the remaining instability of the joint should be assessed during anesthesia. In an awake patient, muscles attached to the joint can simulate stability. The examination is controlled by simultaneous rapid successions of X-rays. In particular, it is important to check how the joint behaves when bending and flexing outwards or inwards. If no further dislocation occurs, conservative treatment is carried out with a 1 to 2-week immobilization of the cast in the functional position (approx. 90° flexion). If there is instability compared to bending outwards or inwards, this period can be increased to 3 weeks. However, physiotherapy should be started as soon as possible to prevent capsule shrinkage and muscle hardening.
If a new elbow dislocation occurs during the functional check, especially when bending, or if the joint cannot be repositioned at all, surgery is indicated. The same applies if instability persists after conservative treatment (immobilization). Surgery is also necessary if there is bone damage or nerve and vascular damage. During this procedure, the joint is repositioned, the bony structures are fixed in their original position, and the capsule-ligament apparatus is restored. An external fixator is often used to fix the joint and its parts. Here, the bony parts are fixed through the skin with screws. There is also a so-called movement fixator, which allows movement within a defined range. The advantage is that movement training can be started earlier. In this way, restrictions of movement as a late consequence should be minimized.
Complications include vascular injuries in about 10% of cases. Especially in arterial vessels, this is an acute emergency due to the high blood pressure prevailing there. Injuries to the nerves (ulnar, median, and radial nerves) with paralysis of the musculature and loss of sensation of touch at typical locations also occur. In a not inconsiderable number of cases, calcification or ossification of the connective tissue (heterotopic ossification) occurs after a dislocation. If these restrict movement, they can be surgically removed. It should be remembered that the operation itself can cause the same phenomenon.
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Prognosis of elbow dislocation
In the case of a conservatively treated simple luxation without concomitant damage, complete recovery can be expected after a prolonged period of stiffness. In about 2 out of 100 cases, a dislocation occurs here.
The more complex the injury, the longer it takes to heal, and the more likely late damage is. This usually includes stiffness with a more limited extension than flexion. Damage to the spoke head, and its stabilizing ligament is likely to restrict the rotation of the forearm.
2% of all patients develop chronic instability with repeated dislocations after an elbow luxation. The cause is usually the lack of stability of the joint-bearing structures after bone fractures.
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