WHAT TYPE OF SHOULDER DISLOCATION DO I HAVE?
Shoulder instability is classified into four categories.
Mechanism - Trauma vs No Trauma
How the dislocation occurs is an important feature in classifying shoulder injuries.
The mechanism of injury may be either traumatic (as a result of external force) or atraumatic (resulting from no external force). Atraumatic injuries are more common in those who are hypermobile or have increased laxity in their shoulder joints. This type of injury may not present with other pathology other than increased shoulder capsule and muscle laxity.
Direction
Typically, this is anterior, posterior, and inferior. It is also possible to have a combination such as anteroinferior. Some people also use the term ' multi directional' to indicate that the shoulder is unstable in more than one direction. Authors differ their opinions as to whether this may be in two different directions or three.
Posterior Dislocations occur when the humeral head (top of the arm bone) is forced posterior to the glenoid fossa (socket). This commonly happens when the arm is forced across the body, or the arm is in front of the body and force is directed through the arm's length.
Inferior Dislocations commonly present with people who are unstable in many directions. While they can be caused by trauma, they are much more common in those that present with an atraumatic mechanism of injury.
Anterior Dislocations occur when the humeral head (top of the arm bone) is forced anterior to the glenoid fossa (socket). This commonly happens when the arm is flung out to the side and either pushed behind the body (hyper extended) or twisted with the hand forced behind the elbow (externally rotated) (see below). Antero-inferior dislocations tend to occur when the arm is raised overhead and twisted backwards or hyper-extended. These two directions make up 95% of all traumatic shoulder dislocations.
A common mechanism for an anterior shoulder dislocation (and the mechanism for many Bankart tears) is when the arm is away from the body and the hand is twisted behind the elbow (Abduction & External Rotation (ABER)) (kindly provided by www.shoulderdoc.co.uk)
Frequency
Shoulder instability is also classified according to the number of times the shoulder has had an instability event. First-time dislocators are commonly called primary dislocators. Once it has happened more than two or three times, it is called recurrent instability.
Severity
Shoulder dislocations art according to the severity of the injury. A dislocation is when the humerus and glenoid fossa (socket) separates and requires manual force to relocate the shoulder.
A subluxation is when there is a momentary or transitory separation of the humeral head from the glenoid fossa and slips back without requiring external force.
Sometimes instability also results in increased movement of the humeral head, which results in impingement and pain. There is no separation in this situation but increased activity of the humeral head, resulting in pain.