What is the most common cause of posterior shoulder dislocation?

The most common cause of posterior shoulder dislocation is a tonic clonic seizure. This is primarily due to the mechanism involved during such seizures, where significant, often violent muscle contractions occur. Such contractions can lead to a forceful contraction of the shoulder muscles, resulting in the dislocation of the humeral head from the glenoid cavity in a posterior direction.

Tonic clonic seizures are characterized by an initial tonic phase, followed by a clonic phase, both of which can exert unintended and excessive force on the shoulder joint, thereby predisposing individuals to posterior dislocation. This type of injury is often under-recognized, as posterior dislocations can be more subtle compared to anterior dislocations and may not present in the typical manner.

In contrast, other causes like a fall from a height or a direct blow to the shoulder more commonly result in anterior shoulder dislocations, which are the most prevalent type. Similarly, overhead throwing injuries are associated with shoulder instability or other types of injuries rather than posterior dislocation specifically. Understanding the mechanism behind shoulder dislocations helps in identifying the likely scenarios that lead to different types of dislocations.