Rotator cuff impingement develops when there is a problem at the acromion, the top front part of the scapula. The acromion forms a sort of bridge or roof over the top of the shoulder that the rotator cuff muscle tendons pass through.
As the arm moves up and down, the rotator cuff tendon slides backwards and forwards through this gap underneath, which is known as the subacromial space. Sitting between the subacromial space and the rotator cuff tendons is the subacromial bursa, a small fluid filled sac that protects the tendons and prevents friction against the bone. The space underneath the acromion is fairly small, and the gap gets narrower as you lift your arm up because of how the bones and tendons move.
Shoulder Impingement Symptoms
Symptoms start off fairly mild but get gradually worse as the condition progresses. Common symptoms of rotator cuff impingement include:
1) Pain: across the shoulder and sometimes extending down to the elbow. People often describe it like a toothache or a sharp pain. To start with, it will only be painful during activities but as the condition progresses, you may develop pain even when resting. Pain tends to be worst when the arm is behind the back, e.g. fastening a bra, or above the head e.g. reaching into high cupboards or hanging up washing
2) Painful Arc: Movements below shoulder height tend not to be painful, but as you raise the arm up above the shoulder, pain develops. Depending on the cause of the impingement, the pain may actually decrease again once the arm is up straight due to the change in position of the bones in the shoulder. In these cases, the most painful part of the movement tends to be from around 70 degrees abduction up to 120degrees, known as a painful arc. This is a classic feature of supraspinatus tendonitis
3) Weakness: the shoulder muscles may start to weaken. This tends to be most noticeable with overhead activities