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Shoulder Instability

Shoulder (glenohumeral) Instability


Shoulder instability refers to excessive movement of the head of humerus (the “ball”) in the glenoid fossa (the “socket”), which can result in pain, dysfunction, loss of movement and loss of strength.  The shoulder joint is designed to allow great flexibility, but the trade-off is the glenoid fossa (the “the socket”) is very shallow predisposing the shoulder to instability.  The common analogy used to describe the shoulder joint is that it is like a golf ball sitting on a tee.



There are two types of shoulder instability – traumatic (dislocation) and atraumatic.

Traumatic instability

Is where there is direct force applied through the shoulder (eg. In a rugby tackle) forcing the humeral head out of the socket (ie. A dislocation).  This stretches and does damage to the soft tissue structures (the labrum, capsule and muscles/tendons) that normally help to hold the humerus in the socket.   Anterior dislocations are by far the most common.  Unfortunately a shoulder dislocation is associated with a very high risk of recurrence (75-90%) in future.  Best practice involves a period of immobilization (sling), followed by physiotherapy exercises to help regain function.  It is essential to then strengthen the rotator cuff muscles to help provide as much muscular stability to the shoulder joint to reduce the risk of recurrence.  Surgical review is also usually recommended, especially for the young, sporty patient who may require intervention to stop recurrent episodes.


Atraumatic instability

Refers to a lax, “loose” shoulder joint that has developed without any specific trauma.  People can have anterior instability (where the humeral head moves too far forward in the glenoid fossa) or multidirectional (the humeral head can move too far in all directions) instability.  There is often not a specific trigger or cause, but the person may complain of shoulder pain made worse when loaded with lifting and/or reaching.  Patients are typically young, female patients who display hypermobility in other joints (eg. Elbows, knees, ankles).


The overwhelming majority of patients with atraumatic instability respond well to conservative management in the form of physiotherapy.  This largely involves rotator cuff and global shoulder strengthening exercises to improve the muscular control of the glenohumeral joint, thereby helping to keep the humeral head centralized in the socket.   Addressing postural factors is also essential, as the ability of the rotator cuff to contract and generate force to hold the humeral head in the socket is largely dependent on the scapula being in an optimal position.  For this reason, often sufferers of atraumatic shoulder instability will present with very rounded, slouched postures which is a big contributing factor to their instability.


In summary, both types of shoulder instability require physiotherapy management to educate patients about best management, and to obtain strengthening programs to improve the active/muscular joint stability in the absence of good passive constraints (ie. The torn/stretched capsule/labrum).  The team at Physio Professionals see shoulder instability frequently, and are highly experienced in helping this group of patients improve their shoulder stability and therefore reduce their episodes of pain.