Rotator Cuff Impingement is a type of rotator cuff injury.
The rotator cuff is a group of muscles and tendons that rotate the arm and holds the arm in to the shoulder joint.

It occurs mainly in people who do physical activities requiring repeated overhead arm movements, as tennis, golf, swimming, weight lifting, or pitching, and those whose profession requires repeated overhead lifting.

It can also be seen when there is an abnormality of the acromion, which can be detected with a Rotator Cuff Radiography.
There are three grades in the shape of the acromion.
Types 1, flat acromion 3% of all cuff tears has this type of acromion;
Types 2, a curved acromion 27% of all cuff tears have this type of acromion;
Type 3, a hooked acromion a majority (70 - 90%) of rotator cuff tears may be seen in patients with type-2 or a type-3 acromion.

The boney hooked acromion impinges on the Rotator Cuff Tendons inflaming them.

Whatever the cause, when the rotator cuff tendons become inflamed and swollen, it is a condition called rotator cuff tendonitis. The swollen rotator cuff gets trapped and pinched under the acromion and can also inflame the bursa, called bursitis.

Pain can extend from the top of the shoulder to the elbow. At the start, the pain comes when the arm is raised then when sleeping on the painful side.

Treatment for a rotator cuff impingement syndrome begins with rest, ice packs, and anti-inflammatory medications. Ultrasound therapy can be used to stimulate the tissues and improve blood flow.
Postural exercises aiming at the position of the Scapular are important.

Avoiding irritating activities may ease this, but if there are ongoing problems when a hooked acromion is present, surgery may be recommended.