Acromion: The lateral extension of the spine of the SCAPULA and the highest point of the SHOULDER.Scapula: Also called the shoulder blade, it is a flat triangular bone, a pair of which form the back part of the shoulder girdle.Acromioclavicular Joint: The gliding joint formed by the outer extremity of the CLAVICLE and the inner margin of the acromion process of the SCAPULA.Shoulder Impingement Syndrome: Compression of the rotator cuff tendons and subacromial bursa between the humeral head and structures that make up the coracoacromial arch and the humeral tuberosities. This condition is associated with subacromial bursitis and rotator cuff (largely supraspinatus) and bicipital tendon inflammation, with or without degenerative changes in the tendon. Pain that is most severe when the arm is abducted in an arc between 40 and 120 degrees, sometimes associated with tears in the rotator cuff, is the chief symptom. (From Jablonski's Dictionary of Syndromes and Eponymic Diseases, 2d ed)Shoulder Joint: The articulation between the head of the HUMERUS and the glenoid cavity of the SCAPULA.Rotator Cuff: The musculotendinous sheath formed by the supraspinatus, infraspinatus, subscapularis, and teres minor muscles. These help stabilize the head of the HUMERUS in the glenoid fossa and allow for rotation of the SHOULDER JOINT about its longitudinal axis.Osteophyte: Bony outgrowth usually found around joints and often seen in conditions such as ARTHRITIS.Glenoid Cavity: A depression in the lateral angle of the scapula that articulates with the head of the HUMERUS.Range of Motion, Articular: The distance and direction to which a bone joint can be extended. Range of motion is a function of the condition of the joints, muscles, and connective tissues involved. Joint flexibility can be improved through appropriate MUSCLE STRETCHING EXERCISES.