“The major difference between impingement and a frozen shoulder is that the arm can actually be raised all the way up once it goes through the painful arc”.
Sub acromial impingement is a fairly common condition. It can be hellishly painful and often causes shoulder
stiffness; for this reason it is often confused with or misdiagnosed as a frozen shoulder. The major difference between impingement and a frozen shoulder is that the arm can actually be raised all the way up once it goes through the painful 'arc'. In a frozen shoulder the stiffness is there in all directions even when someone else tries to lift the arm.
The main symptoms come as you lift your arm up sideways between 70 and 110 degrees; rather confusingly we also call this painful arc syndrome. Painful arc describes the symptom of pain (severe crippling spasm), when the arm is lifted up to shoulder level. You will find it difficult to lye on your affected side at night and getting dressed can be a real ordeal.
Why does it happen?
The space below the collarbone and the top of the shoulder ball is called the sub acromial space. It is a small
space at the best of times and is a vital conduit for nerves, ligaments and blood vessels. It also contains one very important tendon from the supraspinatus muscle. Over time the supraspinatus tendon can rub on the under surface of the collarbone and become inflamed and swollen, this can also lead to swelling of the bursa (an oily pad that stops tendons rubbing). These swollen structures compromise the already narrow space. The main components within the sub acromial space are:
Sub acromial Bursa
Long head of biceps
The shoulder capsule
Various mechanical factors can compromise this space and cause it to become inflamed thus further reducing the already tight space. Risk factors include:
Certain sports such as tennis, baseball and swimming
Aging and degeneration of joint margins
(Osteophytes) especially due to roughening underneath the collarbone
Also, some people have different shaped hooked collarbones, which may predispose to impingement. Left untreated the normal shoulder movement fails and these conditions can precipitate full tears of the rotator cuff.