Unstable Shoulder

The shoulder is a ball-and-socket joint, where the head of the humerus (upper arm bone) and glenoid (socket) of the scapula (shoulder blade) join together.

It is kept in place by groups of ligaments and muscles for stability.

The shoulder joint has good mobility in all directions, but this makes the joint vulnerable to instability issues.

Shoulder instability arises when the tissues surrounding the joint (ligaments and muscles) are unable to properly support the head of the humerus securely within its socket.


  • Born being hypermobile
  • Acute trauma events (e.g. sports injury, fall)
  • Micro trauma events where the shoulder structures are stressed / weakened from overuse or repetitive overhead movements (e.g. throwing sports, manual work)
  • Previous history of shoulder injury or dislocation where some structures in the shoulder were torn or healed too “loosely”


  • A persistent feeling of the shoulder being loose / “dangling” / not in its position
  • Pain or a “clunk” sound in certain positions
  • Repeated incidence of shoulder giving way in specific activities or arm position
  • Pins & needles, numbness or weakness through the arm to the hand (if the nerve is affected)


Diagnosing shoulder instability often starts with a physical exam by a doctor. A doctor will check for weakness, range of motion and looseness. They will also ask you about injuries and shoulder instability history.

A doctor may use further testing:

  • Magnetic resonance imaging (MRI) or computed tomography scan (CT scan)
  • MRI or CT scan can be performed after dye is injected into the shoulder joint (arthro-MRI or arthro-CT)
  • Examination under anesthesia followed by arthroscopy.


Anterior Instability

This is the most common form of shoulder instability where the humeral head is shifted towards the front. It often occurs either from dislocation or subluxation from acute trauma in overhead sport motion (e.g. tennis, baseball).

Posterior Instability

The humeral head is shifted backwards. This occurs less frequently. It often occurs from a trauma fall in outstretched arm or a direct forceful blow to the front of shoulder (e.g. car accident).

Multidirectional Instability

The humeral head can be shifted out of the socket in any direction. This is usually a chronic problem and often due to genetic factors (e.g. groups of people who are very flexible, i.e hypermobile). They are best managed with a thorough shoulder rehabilitation program (Watson et al. 2018) unless a extensive tear in the labral, tendon or ligament has taken place for possible surgery.


  • Avoid / reduce / modify painful activities
  • Sling to rest and immobilize the shoulder (for severe pain and traumatic dislocation)
  • Non-steroidal anti-inflammatory drugs (NSAIDs) for pain control and inflammation
  • Physiotherapy for active pain relief and recovery, restoration of range of motion, strengthening and return to daily activities.