There are a couple of types of shoulder impingement, but the most common is a condition where the rotator cuff insertion, impinges underneath the front of the acromion (a bony process on the scapula) when the arm is raised overhead. Usually this action is performed without any pain or restriction of movement, as a bursae aids the movement of the tendon to slide against the undersurface of the acromion.

Once this bursa is irritated, it can create a cycle of inflammation, pain and thickening which then predisposes to further impingement. Some patients are predisposed to this condition.

The typical clinical test for this is to raise the arm more than 90° forwards above the head, and this reproduces the pain. The bedside test is to then inject the shoulder with some local anaesthetic, and if this removes the pain then it is positive for shoulder impingement. Typically patients do not have a decrease in strength and if this is the case then a rotator cuff tear should be ruled out.