What Is Shoulder Instability?

You stretch to reach something in the back seat of the car or on a high shelf. Suddenly, your shoulder joint feels like it’s slipping out of place. Does this sound familiar? If so, you probably have a condition called shoulder instability. It can happen after parts of your shoulder joint are stretched or damaged. Without these parts to hold the joint tight, your shoulder can slip unexpectedly, moving too far in certain directions.

The Cause of Shoulder Instability

The most common cause of shoulder instability is a shoulder injury. Falling or running into something, damaging your shoulder during sports, or lifting something the wrong way can over-stretch your shoulder joint, loosening the parts of the joint that keep it tight. Once your shoulder joint is loosened, it may be more likely to slip out of the socket again and again.


Common Conditions

Overuse Tendonitis

Shoulder motions used during activities like golfing, pitching, or carrying luggage may cause repetitive stress within the rotator cuff, leading to irritation, bruising, or fraying. This can cause shoulder pain and weakness in the joint.

Impingement Tendonitis

When the space is narrowed between the rotator cuff and the bony acromion above it, the bone pinches and irritates the cuff. This can happen when the cuff is weak, the bursa is swollen, or the acromion angles down too far. Tendonitis caused by impingement can occur with repetitive shoulder activities, such as sports or jobs involving overhead reaching.

Calcification Tendonitis

Inflammation can sometimes result in a build-up of calcium deposits within the rotator cuff, leading to pain and loss of shoulder strength and movement.


Sever tendonitis from impingement, degeneration, or sudden injuries like falling can cause partial or complete tearing of the rotator cuff. This can result in shoulder pain, weakness, and loss of normal movement.