Shoulder Instability:
When the Joint Won't Stay Put

Why the shoulder is especially prone to instability

The shoulder is a ball-and-socket joint, but unlike the hip — where a deep bony socket holds the femoral head firmly in place — the shoulder's socket (the glenoid) is shallow, roughly the size and depth of a golf tee holding a golf ball. That trade-off is what gives the shoulder its enormous range of motion, letting the arm move overhead, behind the back, and across the body in ways the hip never could. The cost of that mobility is stability: the shoulder relies heavily on soft tissue — a rim of cartilage called the labrum, the joint capsule, and the surrounding ligaments and rotator cuff muscles — to keep the humeral head centered in the socket. When those restraints are stretched, torn, or injured, the joint can partially slip (subluxation) or fully separate (dislocation).

The vast majority of dislocations — roughly 95% in most series — occur anteriorly, with the humeral head displaced forward and down out of the socket, typically from a fall onto an outstretched or externally rotated, abducted arm, or a direct blow during contact sport. Posterior and multidirectional instability occur far less often and have somewhat different causes and treatment considerations.

How common it is

Shoulder dislocation is one of the most frequent major joint dislocations seen in emergency departments. A widely cited analysis of United States emergency department data estimated the overall incidence of shoulder dislocation at 23.9 per 100,000 person-years, with men affected at roughly 2.6 times the rate of women. The pattern is strongly age-dependent: incidence peaks sharply in the second and third decades of life, driven largely by sports and high-energy trauma in young, active men, with a second smaller peak in older adults related to falls.

Within young, physically active populations the numbers are considerably higher — studies of military academy cadets and collegiate or high-school athletes report incidence rates many times greater than the general population figure, reflecting the combination of youth, contact exposure, and physical intensity that makes this largely a young person's injury.

First-time dislocation versus recurrent instability

Clinically, it helps to separate two different problems that are often discussed together. A first-time traumatic dislocation is an acute event, usually requiring reduction (putting the joint back in place), most often performed in an emergency department. Recurrent instability refers to a shoulder that dislocates or subluxates repeatedly, sometimes with progressively less force required each time. The two are closely linked: a first dislocation, particularly in a young or athletic patient, substantially raises the risk of a second one, and each subsequent episode tends to cause further damage to the labrum, capsule, and sometimes the bone of the glenoid or humeral head (a compression fracture known as a Hill-Sachs lesion).

How the diagnosis is made

An acute dislocation is usually obvious clinically — visible deformity, severe pain, and an inability to move the arm — and is confirmed with a plain X-ray both before and after reduction, to document the dislocation and rule out an associated fracture. Once the acute episode has settled, or when a patient presents with ongoing instability rather than a fresh injury, the evaluation shifts to examining the labrum, capsule, and bone in more detail.

Physical examination tests such as the apprehension test (positioning the arm to reproduce the sensation of the shoulder about to slip out) and the relocation test are used to help localize the direction and severity of instability. MRI, often performed with an intra-articular contrast injection (MR arthrography), is the standard imaging tool for assessing labral tears and capsular injury, while CT scanning is frequently used when surgery is being considered, because it more precisely quantifies bone loss on the glenoid — a measurement that significantly affects which surgical procedure is likely to succeed.

What the evidence says about a first-time dislocation

After a first dislocation is reduced, the traditional approach has been a period of immobilization in a sling followed by physical therapy, reserving surgery for patients who go on to have recurrent instability. In recent years this default has been increasingly questioned for younger, higher-risk patients.

This doesn't mean every first-time dislocation needs surgery — the decision depends heavily on age, sport, occupation, and the amount of bone or soft tissue damage seen on imaging — but it does mean the old assumption that surgery should always wait until after a second or third dislocation is no longer the uncontested standard, particularly for younger patients in contact sports.

What the evidence says about recurrent instability

For patients who do go on to have recurrent instability, surgery is generally recommended, and the central decision becomes which procedure: an arthroscopic soft-tissue repair (Bankart repair, which reattaches the torn labrum to the glenoid rim) or an open bone-block procedure (the Latarjet procedure, which transfers a piece of the coracoid bone to rebuild the front of the socket and add a soft-tissue sling effect). The choice depends substantially on how much bone has been lost from the glenoid.

	Arthroscopic Bankart repair	Latarjet procedure
Approach	Minimally invasive, reattaches torn labrum/capsule	Open, transfers bone graft to rebuild glenoid
Best suited for	Little to no glenoid bone loss	Significant glenoid bone loss, high-risk contact athletes, or after a failed prior repair
Recovery	Generally shorter, less invasive rehabilitation	Longer recovery given the bony healing required
Recurrence risk	Higher in studies directly comparing the two, particularly in contact athletes and with bone loss	Generally lower recurrence in comparative studies, at the cost of a more invasive procedure

When to see a specialist

Any shoulder dislocation warrants prompt medical attention for reduction and to rule out an associated fracture or nerve injury. After the acute episode, a specialist evaluation is worthwhile even if the shoulder feels fine — particularly for younger patients, athletes in contact or overhead sports, or anyone who notices the shoulder repeatedly feeling loose, catching, or "wanting to pop out," since the pattern of recurrence and the extent of bone or soft-tissue damage both influence how the problem is best managed, and outcomes are generally better when treatment decisions are made with full information rather than after several repeat episodes.