Chapter 277

Shoulder pain is usually caused by problems local to the shoulder joint or the supporting or adjacent structures. However, the shoulder is a site of referred pain from serious conditions such as myocardial infarction or diaphragmatic irritation from intra-abdominal bleeding or hollow viscus perforation.

This chapter details disorders of the shoulder joint and structures deep to the joint. For a discussion of cardiac and intra-abdominal disorders that may present with shoulder pain, the reader is referred to Section 7, Cardiovascular Disease, and Section 9, Gastrointestinal Emergencies.

The most common causes of nontraumatic shoulder pain, in descending order of frequency, are rotator cuff tendinopathy, impingement, acromioclavicular joint disease, adhesive capsulitis, and referred pain.1 After neck and back pain, shoulder pain is the most common type of musculoskeletal pain, accounting for approximately 16% of all musculoskeletal complaints.2,3 The sex- and age-standardized incidence of chronic shoulder pain is approximately 9.5 per 1000 [95% CI (7.9 to 11.2 per 1000)].3 Disability from shoulder disease ranks in severity with that from conditions such as congestive cardiac failure, acute myocardial infarction, diabetes mellitus, and clinical depression.3

Overuse can produce pathologic changes in the rotator cuff structures that progress along a continuum starting with subacromial bursitis from mechanical irritation, progressing to rotator cuff tendinitis, and eventually leading to partial- and full-thickness rotator cuff tears. Laborers who work with their arms above the horizontal and athletes of all ages, especially throwers, swimmers, and racquet sports enthusiasts, are the most susceptible to chronic overuse injuries.

Conditions affecting other intrinsic structures of the shoulder complex can also cause pain. In addition, extrinsic disorders can refer pain to the shoulder and must be considered in the differential diagnosis. A focused history and physical examination carried out with an understanding of the complex anatomy and function of the shoulder is essential in determining the source of shoulder pain. Establishing the proper diagnosis, initiating the appropriate treatment, and making timely referrals for follow-up are critical in preserving the function and mobility of the shoulder.

The shoulder is designed for mobility in all directional planes, rather than for stability. Its functions are to help position the hand and upper extremity for accurate and efficient use, and to provide strength and power to upper extremity movements. To meet the many demands placed on it, the shoulder uses three bones, four joints, and a specialized set of soft tissues consisting of muscles, tendons, ligaments, and bursae.

### Bones and Joints

The humerus, clavicle, and scapula make up the bony structures of the shoulder complex. The scapula is the most complex bone and consists of the body and three bony extensions: the glenoid, the coracoid, and the acromion.

The four joints of the shoulder are the glenohumeral, acromioclavicular, sternoclavicular, and scapulothoracic. The glenohumeral joint is a ball-and-socket joint and is the central axis of shoulder motion. ...

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