The shoulder is the most mobile, and least stable, joint in the human body, allowing movement in multiple planes. Shoulder instability happens when the head of the upper arm bone (humerus) can't stay properly centered in the shoulder socket (glenoid fossa) during movement.
Instability exists on a spectrum. Sometimes the humeral head partially slips beyond normal limits while still touching the socket; this is a subluxation. In more severe cases, it moves completely beyond the rim of the socket, resulting in a dislocation. When the surrounding structures can no longer control this motion, symptoms such as pain, weakness and loss of function often develop.
The shoulder joint relies on a complex balance of static and dynamic stabilizers. When one or more of these are compromised, through trauma, repetitive stress or connective tissue laxity, instability can develop. Common injuries associated with shoulder instability include subluxation, dislocation (with or without reduction), rotator cuff tears, Hill-Sachs lesions and Bankart lesions.
Anatomy of shoulder stability
| Static stabilizers (passive) | Dynamic stabilizers (active) |
|---|---|
| Glenoid labrum | Rotator cuff: supraspinatus, infraspinatus, teres minor, subscapularis |
| Joint capsule | Periscapular muscles: serratus anterior, rhomboids, trapezius, latissimus dorsi, pectoralis minor |
| Glenohumeral ligaments | Deltoid |
| Negative intra-articular pressure |
Proper coordination between these stabilizers is essential for shoulder health.
Types of shoulder instability
Anterior shoulder instability
Anterior instability is the most common type, accounting for about 95% of instability events. It occurs when the humeral head slides forward, often with the arm raised out to the side and rotated outward (abduction and external rotation). It can result from traumatic events such as falls or collisions, or from repetitive overhead movements.
Anterior instability is more common in younger people because of ligament laxity, while adults over 40 more often have instability related to rotator cuff tears. Higher-risk sports include baseball, volleyball and swimming.
Posterior shoulder instability
Posterior instability is less common, about 2–5% of cases, but still seen in active people. It typically occurs when the shoulder is in flexion, adduction and internal rotation, and may result from repetitive microtrauma or high-force trauma. It's more often seen in men ages 20–30, particularly in weightlifting and contact sports such as football.
Multidirectional shoulder instability
Multidirectional instability involves instability in two or more directions (anterior, posterior and/or inferior). It's most common in people ages 20–30 and is often associated with repetitive microtrauma from overhead activities. It may also be linked to generalized joint laxity in conditions such as Ehlers-Danlos syndrome, Marfan syndrome, osteogenesis imperfecta and hypermobility spectrum disorders. (Related: why people with hypermobile joints always feel like they need to stretch.)
Common signs and symptoms
- Shoulder pain (front, back or a deep ache)
- Weakness or fatigue
- Popping, clicking or catching sensations
- Neurological symptoms (tingling or burning)
- Crepitus
- Excessive range of motion
- Poor dynamic control
Treatment options for shoulder instability
Physical therapy is typically the first line of treatment and has been shown to be highly effective, particularly for adults over 40 and people not involved in high-demand overhead sports. Conservative management focuses on scapular posture and control, strengthening the dynamic stabilizers, proprioception and neuromuscular control, and functional and sport-specific training.
Research supports that a comprehensive, individualized rehab program can significantly reduce symptoms and often help patients avoid surgery. For younger athletes in high-demand overhead or contact sports, surgery may be recommended after an acute dislocation because of a higher risk of recurrent instability. After immobilization, physical therapy is essential to restore function and return to sport safely.
Examples of helpful exercises
- Plank and single-arm plank
- Side plank variations
- Plank drags
- High plank on unstable surfaces
- Isometric internal and external rotation walkouts
- Prone T's, W's and Y's
- Carries (farmer's, waiter's, overhead)
- PNF diagonal patterns
- Jobe's rotator cuff exercises
Exercise selection should always be tailored to your symptoms, goals and activity demands.
Dealing with a shoulder that feels loose, slips or has dislocated? Our physical therapists can build a stability program tailored to you.
book a sessionthe takeaway
Shoulder instability ranges from partial slips (subluxation) to full dislocation. Anterior instability accounts for about 95% of cases. Physical therapy focused on scapular control, rotator cuff strength and neuromuscular control is the first-line treatment, while young athletes in high-demand sports may need surgery after a dislocation.
Frequently asked questions
What is the difference between a subluxation and a dislocation?
In a subluxation, the humeral head partially slips beyond normal limits but stays in contact with the socket. In a dislocation, it moves completely beyond the rim of the socket.
What is the most common type of shoulder instability?
Anterior instability, which accounts for about 95% of instability events and often happens with the arm raised and rotated outward.
Can physical therapy fix shoulder instability?
Physical therapy is the first line of treatment and is highly effective, especially for adults over 40 and people not in high-demand overhead sports. A comprehensive rehab program can often help patients avoid surgery.
When is surgery recommended for shoulder instability?
For younger athletes in high-demand overhead or contact sports, surgery may be recommended after an acute dislocation because of a higher risk of recurrence, followed by physical therapy.
