Impingement is a way of describing the catching or rubbing of the rotator cuff tendons and the fluid filled sac (bursa) on the bones and ligaments in the top of the shoulder. This can lead to inflammation and pain in the top part of the shoulder (bursitis).
Why does it happen?
It occurs for a variety of reasons which we think of as either
Intrinsic – this is due to a muscle imbalance, fatigue or wear and tear of the tendons. In these situations, the muscles are not working as well to hold the humeral head (ball) in the centre of the glenoid (socket). This can be a result of overuse from heavy work or due to poor posture in a more desk/driving based job. Muscle imbalances can occur even in sporting individuals despite taking part in regular exercise. This is usually caused by the stronger more well developed muscles at the front of the shoulder overpowering the weaker less well used muscles at the back. Finally, age related wear and tear of the muscles from years of use can lead to impingement syndrome.
Extrinsic – this is where bony spurs and thickened ligaments in the top of the shoulder rub and wear the tendons of the rotator cuff and the bursa. These bony overgrowths tend to develop with age and are more likely to cause pain when the arm is in certain positions such as reaching forwards, twisting the arm and performing overhead tasks and sports. It is not clear why these spurs and thickened ligaments develop but it is likely that they are related to wear and tear and prolonged use of the shoulder.
What are the symptoms and signs?
Most people experience pain at the side of the shoulder and upper arm. It is usually worse with movements such as reaching out to the side, reaching around your back or performing overhead tasks. Sleep is often affected by the discomfort. Some people also describe weakness in the shoulder. This is commonly due to pain and as such it is common to avoid certain activities. Painful clicking and catching is also a common complaint. Painless clicking however also occurs in many normal shoulders and is not always a sign of a shoulder problem.