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
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.
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. Although the glenohumeral
joint is the most mobile joint in the body, it is the least stable.
To help improve its stability, this joint relies on three components. The
first is the glenoid labrum, which is a fibrous ring of tissue encircling the
glenoid cavity. The glenoid labrum increases the surface contact
area of the humeral head within the relatively shallow glenoid fossa.
The second component consists of three glenohumeral ligaments, which
aid stability by reinforcing the joint capsule. Finally, four specialized
muscles, known as the rotator cuff, encompass the
glenohumeral joint and provide significant stability during motion.
The sternoclavicular and acromioclavicular joints work together
to contribute to glenohumeral motion, but their primary function
is to suspend and to stabilize the shoulder girdle.2 Rotation
at the acromioclavicular joint and elevation at the sternoclavicular
joint allow complete arm elevation. The scapulothoracic joint represents
the articulation of the scapula on the posterior wall of the thorax.
Scapular motion is essential for overall shoulder motion: every
degree of scapulothoracic motion allows 2 degrees of glenohumeral
The deltoid, which drapes the shoulder complex and forms its
contour, acts as a powerful and independent elevator of the arm.
Along with the pectoralis, the deltoid is the primary source of
movement of the upper extremity.
The rotator cuff consists of four muscles: supraspinatus, infraspinatus, teres
minor, and subscapularis (Figures 277-1 and 277-2).
All originate on the scapula, traverse the glenohumeral joint, and
insert on the proximal humerus. The rotator cuff functions primarily
as a dynamic stabilizer of the glenohumeral joint. The rotator cuff
muscles also contribute significantly to the power of the upper
extremity, providing 30% to 50% of the power in
abduction and 90% in external rotation.
Posterior view of the shoulder illustrating rotator cuff muscles.
Anterior view of the shoulder illustrating the supraspinatus
muscle and the long head of the biceps.
The supraspinatus muscle originates on the posterior and superior
aspect of the scapula, passes beneath the acromion, and inserts
on the great tuberosity of the humeral head. It initiates arm elevation
and abducts the shoulder. It also balances the power of the deltoid,
keeping the humerus centered in the glenoid during deltoid contraction.
The infraspinatus originates on the posterior scapula just inferior
to the scapular spine. It inserts on the posterior aspect of the
greater tuberosity and acts primarily as an external rotator of
the arm (Figure 277-1). The teres minor originates
on the lateral border of the scapula just inferior to the infraspinatus
and inserts on the posterior aspect of the humerus. It works with
the infraspinatus to provide external rotation (Figure
277-1). The subscapularis is the only rotator cuff muscle ...