Shoulder instability

Shoulder instability is a tendency of glenohumeral joint to sublux or dislocate. This happens due to damage to the functional and anatomical stabilizers of glenohumeral joint. 

Static stabilizers of glenohumeral joint are:

- articular surface

- labrum

- glenohumeral ligaments

- glenohumeral joint capsule

- coracoacromial arch 

- negative adhesive force

Dynamic or functional stabilizers of glenohumeral joint

- rotator cuff

- long head of biceps tendon

Types of shoulder instability

There are 4 types of shoulder instability: anterior, posterior, multidirectional and superior shoulder instability. 

Anterior shoulder instability is the most common type, accounting for up to 95% of all cases and this usually results from anterior glenolabral injury, particularly from disruption of the anterior band of the IGHL. 

Posterior shoulder instability is rare, and is usually results from posterior glenolabral injury, particularly from the disruption of posterior band of IGHL. 

Multidirectional shoulder instability usually not due to previous dislocation, but rather congenital joint laxity. Multidirectional shoulder instability is usually bilateral. 

Superior shoulder instability is usually associated with multidirectional instability. 

So, in these cases of shoulder instability, as a result of greater mobility we can see some secondary changes including subacromial spur formation, hyperthrophy of the greater tuberosity and coracoacromial ligament hyperthrophy.