What muscles and structures are involved in shoulder impingement, and how can massage therapy help treat this condition?

Shoulder impingement involves pinching of structures like the supraspinatus tendon, subacromial bursa, and long head of the biceps tendon between the head of the humerus and the coracoacromial arch formed by the acromion and coracoid process. Key muscles involved include the rotator cuff (supraspinatus, infraspinatus) as well as scapular stabilizers like the rhomboids, trapezius, and serratus anterior. Overactive muscles that contribute to impingement include pectoralis major/minor and latissimus dorsi. 

Massage therapy can help treat impingement by releasing tight anterior muscles like the pecs to reposition the scapula, addressing trigger points in posterior scapular stabilizers that are overworked trying to compensate, and improving scapulohumeral rhythm. Techniques like pin and stretch help mobilize tissues, while joint mobilizations can help restore motion. It's important to work all muscles affecting scapular position rather than just the rotator cuff. Restoring optimal alignment and coordination of the shoulder complex structures is key.