The following information is from the American Society of Hand Therapists and is available as a handout from their website: http://www.asht.org.
What is shoulder impingement?
The rotator cuff is a group of muscles and tendons in the shoulder that connect the bone in the upper arm (humerus) to the shoulder blade (scapula). The rotator cuff allows for stability and flexibility while moving the shoulder. Impingement happens when the muscles and soft tissues around the rotator cuff are pinched or squeezed. This pinching occurs between the humerus and the front of the shoulder blade called the acromion.

What causes shoulder impingement?
There are several factors that contribute to shoulder impingement. The shape of the acromion can pinch on the tissues in the shoulder causing impingement. Weakness of the shoulder muscles along with poor posture can cause impingement. Impingement may also be the result of repetitive shoulder motion, such as throwing a ball or reaching overhead.
What are the symptoms of shoulder impingement?
Shoulder impingement is one of the most common causes of pain in the shoulder. The pain usually develops after performing activities that involve reaching behind the back or above the head. Pain caused by shoulder impingement may be mild at first, and then become worse while performing activities and while sleeping.
What is the treatment for shoulder impingement?
Nonsurgical treatment includes rest, changing the ways activities are performed and a referral to therapy to instruct in exercises for posture and stretching. If the symptoms do not improve with therapy, the physician my recommend a cortisone injection or surgery. Surgery involves widening the space in the shoulder to decrease the pressure on the rotator cuff. Therapy also plays an important role in recovery after surgery.
What can a hand therapist do for me?
A hand therapist can help evaluate the cause of shoulder impingement, determine which activities aggravate the symptoms, and also provide treatment to decrease pain. After surgery, the hand therapist will provide instruction in exercises to restore flexibility and strength around the shoulder joint.