Shoulder impingement is not a diagnosis, but a syndrome that refers to a specific presentation of shoulder symptoms and signs which could be a part of various conditions.
The term impingement refers to catching or rubbing of the shoulder tendons (the rotator cuff) against the tip of the shoulder blade (acromion) or any bony outgrowths from the acromioclavicular joint.
Shoulder impingement is common in middle aged men but can occur in women too. It usually presents with spontaneous onset of pain over the shoulder or in the upper arm. This pain is worse when raising the arm to the side, over-head or when reaching backwards. Patients may sometimes have pain at night too. Weakness and stiffness may also be a feature.
Conditions that lead to narrowing of the space between the tendons and the acromion will present with impingement syndrome. These conditions include acromial bony spurs, osteophytes from an arthritic acromio-clavicular joint (ACJ), rotator cuff tendon tears, calcific tendonitis, labral (cartilage) tears, instability, etc. It is important to identify the cause when planning treatment.