Orthopedics focuses on the musculoskeletal system. Learn about the diagnosis, treatment, and rehabilitation of bone, joint, ligament, and muscle conditions.
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A shoulder doesn’t just pop out for no reason; it requires force or a structural failure. Understanding the cause of your dislocation is critical for treatment. Was it a high-impact tackle? A seizure? Or did it just slip out while you were reaching for a seatbelt? The answer tells the doctor about the quality of your tissues and the severity of the damage.
This section explores the various ways a shoulder can dislocate. We will look at the mechanics of traumatic injuries in sports, the unique causes of posterior dislocations, and the genetic factors that make some people “loose-jointed” and prone to instability without any trauma at all. We will also discuss the concept of “bone loss,” a serious complication of recurrent dislocations that can change the shape of your socket over time.
This is the most common cause. It involves a significant force applied to the shoulder. In sports, this often happens when the arm is abducted (out to the side) and externally rotated (hand up), like the position of a quarterback about to throw. If the arm is hit backward while in this vulnerable position, the lever force pries the ball out of the socket anteriorly (to the front).
Falls are another major cause. Falling on an outstretched hand transmits force up the arm and drives the humerus head forward. Car accidents can also generate the high energy needed to dislocate a healthy shoulder. In these traumatic cases, the soft tissues are almost always torn (Bankart lesion) because they were strong enough to resist until they failed catastrophically.
Some people have “loose” shoulders without ever having a major injury. This is often due to generalized ligamentous laxity, sometimes called being “double-jointed.” Their ligaments are naturally stretchy and elastic throughout their body.
In these patients, the shoulder might slip out of joint (subluxate) with normal daily activities like swimming, reaching overhead, or even sleeping. This is called Multidirectional Instability (MDI) because the shoulder can often slide out in multiple directions (front, back, and down). For these patients, the problem isn’t a torn ligament but rather a “baggy” capsule that doesn’t hold the ball tightly. Surgery is less successful here; the focus is usually on strengthening the rotator cuff muscles to act as dynamic stabilizers.
Dislocating out the back (posterior) is rare and often missed on initial X-rays. It happens when the arm is forced straight back while held in front of the body. The classic causes are the “3 Es”: epilepsy (seizures), electrocution, and ethanol (alcohol-related falls).
During a seizure or electric shock, the internal rotator muscles of the shoulder (which are stronger than the external rotators) contract violently. This massive muscle imbalance overpowers the joint and drives the ball out the back of the socket. Because the arm is usually locked in internal rotation (hand against stomach) afterwards, it can be mistaken for a “frozen shoulder” if not X-rayed carefully.
When the shoulder dislocates, the ball doesn’t just float in space; it crashes against the rim of the socket. The head of the humerus is relatively soft bone compared to the rigid rim of the glenoid. This impact creates a dent or divot in the back of the humeral head, known as a Hill-Sachs lesion.
Think of it like a dent in a ping-pong ball. If this dent is large enough, it can catch on the socket rim every time you move your arm, causing the shoulder to pop out again easily. Conversely, the rim of the socket itself can fracture or wear down (Bony Bankart), making the socket even shallower. This bone loss is a major reason why some shoulders fail to stabilize even with surgery and require complex bone-grafting procedures (like the Latarjet procedure) to fix.
Your genetics determine the quality of your collagen, the protein that makes up ligaments. Conditions like Ehlers-Danlos Syndrome (EDS) or Marfan Syndrome affect collagen structure, making ligaments excessively stretchy.
People with these conditions are prone to dislocations not just in the shoulder but also in the kneecap and other joints. Recognizing a collagen disorder is vital because standard tightening surgeries often fail as the tissues simply stretch out again. Treatment focuses heavily on muscle strengthening and avoiding high-risk positions.
Swimmers, baseball pitchers, and volleyball players put their shoulders in extreme positions thousands of times a season. This repetitive stretching can slowly elongate the ligaments over time.
Initially, this “acquired laxity” may enhance performance by enabling a longer reach or a harder throw, but over time, it may lead to instability. The ligaments become too loose to center the ball, leading to pain, labral tears, and eventual dislocation. This condition is a wear-and-tear instability rather than a single traumatic event.
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Yes, if you have severe instability or loose ligaments. Sleeping with your arm under your head or in an abducted position can allow the shoulder to slide out if the muscles are fully relaxed.
Certain exercises, like wide-grip bench press and behind-the-neck pulldowns, put the shoulder in the “danger zone” (abduction/external rotation). Heavy loading in this position can force the shoulder out, especially if you have pre-existing laxity.
Yes. The muscle contractions during a tonic-clonic seizure are strong enough to dislocate the shoulder and sometimes even fracture the humeral head or neck simultaneously.
Not necessarily. With proper rehab and sometimes surgery, many people regain a fully functional, stable shoulder. However, the risk of re-injury remains higher than in a never-injured shoulder.
Yes. Young patients (under 20) have a very high recurrence rate (up to 90%) due to their active lifestyles and elastic tissues. Patients over 40 have a much lower recurrence rate but a much higher risk of tearing their rotator cuff during the dislocation.
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