The shoulder joint is called a ball-and-socket joint. The ball is the rounded top of the bone in the upper arm (humerus), which fits into the socket — the cup-shaped outer part of the shoulder blade. When the top of the humerus moves out of its usual location in the shoulder joint, the shoulder is said to be dislocated. A related injury called a shoulder subluxation occurs when the top of the humerus is only partially displaced and not totally out of its socket.
In some cases, a shoulder is dislocated when the arm is pulled or twisted with extreme force in an outward, upward or backward direction. This extreme force literally pops the top of the humerus out of its socket. In other cases, a shoulder dislocation is the result of a fall on an outstretched arm, a direct forceful blow to the shoulder, a seizure or a severe electric shock. Seizures and shock can cause shoulder dislocations because they produce extreme, unbalanced muscle contractions that can wrench the humerus out of place.
Types of Dislocations
Shoulder dislocations can be separated into three different categories based on the direction of the dislocation.
Anterior dislocation — The top of the humerus is displaced forward, toward the front of the body. This is the most common type of shoulder dislocation, accounting for more than 95% of cases. In young people, the cause is typically sports-related. In older people, it usually is caused by a fall on an outstretched arm.
Posterior dislocation — The top of the humerus is displaced toward the back of the body. Posterior dislocations account for 2% to 4% of all shoulder dislocations and are the type most likely to be related to seizures and electric shock. Posterior dislocations also can happen because of a fall on an outstretched arm or a blow to the front of the shoulder.
Inferior dislocation — The top of the humerus is displaced downward. This type of shoulder dislocation is the rarest, occurring in only one out of every 200 cases. It can be caused by various types of trauma in which the arm is pushed violently downward.
Symptoms of a dislocated shoulder include severe pain, limited range of motion, and distortion to the contour of the shoulder. First time dislocations almost always require an external force to help relocate – whether this be an on-field Physiotherapist or in the emergency room in the hospital.
Following a shoulder dislocation you can suffer from shoulder instability. Shoulder instability is a problem that occurs when the structures that surround the shoulder joint do not work to maintain the ball within its socket. Instability is often associated with subluxation, which may be associated with pain and/or dead arm sensation. In some people, this is not actually painful but can be quite annoying and prevent them from taking part in daily activities or sports.
Instability of the shoulder joint can be in one direction, e.g. anterior instability (out the front), posterior instability (out the back) or in more than one direction (known as multidirectional instability). The most common form of instability seems to be anterior and is probably because the joint capsule is at its weakest at the front of the joint – additionally because most dislocations are anterior.
How can Physiotherapy help?
Physiotherapy treatment of the shoulder depends on several factors, and always begins conservatively. Specific strengthening exercises will often help maintain shoulder stability. It takes several months of strengthening before you can assess its effectiveness.
If conservatively treatment fails to improve your symptoms, there are surgical options that may be considered depending on your cause and direction of instability.
