Shoulder impingement is characterised by pain in the shoulder usually going into the upper arm and often down towards your elbow.
Shoulder motion is restricted principally on elevating the limb to the side. The pain often prevents you getting your hand behind your back. Lying on your affected shoulder at night often causes pain resulting in you waking. The symptoms can come on acutely for single, or several short, episodes. Episodes may become a recurring or constant problem.
The subacromial space between the acromion and humeral head is narrowed when the shoulder is in certain positions. In subacromial impingement, the rotator cuff tendons and bursa tend to become swollen (often called bursitis). In the majority of people the undersurface of the acromion is flat (type I) but for some people the undersurface can be curved (type 2) or hooked (type 3) with type 2 and 3 acromions reducing the space available for the tendons and the bursa.