Impingement occurs when the rotator cuff tendons are repetitively pinched under the shelf of bone at the top of the shoulder called the acromion. The irritation leads to swelling of the tendons. Many cases develop suddenly after increasing activity while others develop slowly over time as a result of degenerative changes around the shoulder. Most patients describe a sharp pain in the upper/front part of the arm when lifting the arm out straight in front. Motion is preserved, but painful. Initial treatment includes activity modification, anti-inflammatory medication and corticosteroid injection. If the condition persists physical therapy is often helpful. In refractory cases, an MRI may further elucidate the degree of tendon degeneration. In some cases, an arthroscopic surgical procedure will be beneficial. Most patients recover quickly after surgery and are able to return to work within 2-3 weeks.