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86 m a s s a g e & b o d y wo r k j u l y/a u g u s t 2 0 2 1 Shoulder pain and stiffness are common upper extremity complaints. Estimates are pain felt under the acromion process (called subacromial pain) may encompass somewhere between 44 and 66 percent of all shoulder complaints seen by orthopedists. 1 For many years, shoulder pathology in this region was called subacromial impingement syndrome (SIS), which indicates tissue compression (impingement) as a primary cause. Interestingly, recent research indicates mechanical impingement may not be the primary cause of pain in some cases. Today, researchers advise renaming this condition subacromial pain syndrome (SAPS) to more broadly include all the various pathological causes for subacromial pain. SAPS can include a spectrum of pathologies, such as partial thickness rotator cuff tears, rotator cuff tendinosis, calcific tendinitis, and subacromial bursitis, as well as metabolic, inflammatory, and degenerative changes in the tendon. In this column, we explore the multiple causes of subacromial pain, look at a variety of treatment strategies, and explore where massage therapy may play a role in reducing this debilitating condition. ANATOMY AND BIOMECHANICS Our exploration of SAPS begins with a review of key anatomical structures in the region. The scapula plays a primary role in subacromial pain and has two prominent bony projections. The first is the acromion process, which is out to the lateral edge of the shoulder. The second is the coracoid process, which angles off in an anterior direction. The coracoacromial ligament spans between these two bony projections. The expanse, including the acromion process, coracoacromial ligament, and coracoid process, is referred to as the coracoacromial arch (Image 1). Subacromial pain is most commonly thought to arise from tissue irritation under the acromion process but could also occur from irritation under other parts of the coracoacromial arch. The region under the coracoacromial arch is anatomically unique. There are very few places in the body where soft tissues get pinched between adjacent bones or ligaments. The space underneath the arch is relatively small and susceptible for soft-tissue compression. In addition, dysfunctional scapular mechanics can play a role in these problems. For example, the scapula must move in upward rotation during shoulder abduction movements. If it does not fully rotate upward, the humerus is more likely to pinch soft tissues against the underside of the acromion process. Often, a nerve in the cervical region, the long thoracic nerve, may be responsible for these dysfunctional shoulder mechanics. The long thoracic nerve is a motor nerve that innervates the serratus anterior muscle. Compression of the long thoracic nerve (near the brachial plexus) may cause weakness of the serratus anterior muscle. Weakness in the serratus anterior leads to inadequate upward scapular rotation during abduction and the resulting subacromial compression. This sequence of events is an example of how nerve compression near the neck can lead to soft-tissue compression in the lateral shoulder. Another potential cause of subacromial impingement is excessive translation or movement of the glenohumeral head during shoulder motions. For example, the rotator cuff and biceps brachii muscles play technique | CLINICAL EXPLORATIONS The Puzzling World of Subacromial Pain BY WHITNEY LOWE Coracoacromial arch. Image from 3D4Medical's Complete Anatomy application. 1 Acromion process Coracoacromial ligament Coracoid process