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What Are the Most Common Shoulder Problems?
The most movable joint in the body, the shoulder is also
one of the most potentially unstable joints. As a result,
it is the site of many common problems. They include sprains,
strains, dislocations, separations, tendinitis, bursitis,
torn rotator cuffs, frozen shoulder, fractures, and arthritis.
Specific shoulder problems will be discussed later in this
booklet.
How Common Are Shoulder Problems?
According to the Centers for Disease Control and Prevention,
about 13.7 million people in the United States sought medical
care in 2003 for shoulder problems.
What Are the Structures of the Shoulder and How Does It
Function?
To better understand shoulder problems and how they occur,
it helps to begin with an explanation of the shoulder’s
structure and how it functions.
The shoulder joint is composed of three bones: the clavicle
(collarbone), the scapula (shoulder blade), and the humerus
(upper arm bone). (See diagram.) Two joints facilitate shoulder
movement. The acromioclavicular (ah-KRO-me-o-klah-VIK-u-lahr;
AC) joint is located between the acromion (ah-KRO-me-on;
part of the scapula that forms the highest point of the shoulder)
and the clavicle. The glenohumeral joint, commonly called
the shoulder joint, is a ball-and-socket-type joint that
helps move the shoulder forward and backward and allows the
arm to rotate in a circular fashion or hinge out and up away
from the body. (The “ball,” or humerus, is the
top, rounded portion of the upper arm bone; the “socket,” or
glenoid, is a dish-shaped part of the outer edge of the scapula
into which the ball fits.) The capsule is a soft tissue envelope
that encircles the glenohumeral joint. It is lined by a thin,
smooth synovial membrane.
In contrast to the hip joint, which more closely approximates
a true ball and socket joint, the shoulder joint can be compared
to a golf ball and tee, in which the ball can easily slip
off the flat tee. Because the bones provide little inherent
stability to the shoulder joint, it is highly dependent on
surrounding soft tissues such as capsule ligaments and the
muscles surrounding the rotator cuff to hold the ball in
place. Whereas the hip joint is inherently quite stable because
of the encircling bony anatomy, it also is relatively immobile.
The shoulder, on the other hand, is relatively unstable but
highly mobile, allowing an individual to place the hand in
numerous positions. It is in fact, one of the most mobile
joints in the human body.
The bones of the shoulder are held in place by muscles,
tendons, and ligaments. Tendons are tough cords of tissue
that attach the shoulder muscles to bone and assist the muscles
in moving the shoulder. Ligaments attach shoulder bones to
each other, providing stability. For example, the front of
the joint capsule is anchored by three glenohumeral ligaments.
The rotator cuff is a structure composed of tendons that
work along with associated muscles to hold the ball at the
top of the humerus in the glenoid socket and provide mobility
and strength to the shoulder joint. Two filmy sac-like structures
called bursae permit smooth gliding between bones, muscles,
and tendons. They cushion and protect the rotator cuff from
the bony arch of the acromion.
What Are the Origins and Causes of Shoulder Problems?
The shoulder is easily injured because the ball of the upper
arm is larger than the shoulder socket that holds it. To
remain stable, the shoulder must be anchored by its muscles,
tendons, and ligaments.
Although the shoulder is easily injured during sporting
activities and manual labor, the primary source of shoulder
problems appears to be the natural age-related degeneration
of the surrounding soft tissues such as those found in the
rotator cuff. The incidence of rotator cuff problems rises
dramatically as a function of age and is generally seen among
individuals who are more than 60 years old. Often, the dominant
and nondominant arm will be affected to a similar degree.
Overuse of the shoulder can lead to more rapid age-related
deterioration.
Shoulder pain may be localized or may be felt in areas around
the shoulder or down the arm. Disease within the body (such
as gallbladder, liver, or heart disease, or disease of the
cervical spine of the neck) also may generate pain that travels
along nerves to the shoulder. However, these other causes
of shoulder pain are beyond the scope of this book, which
will focus on problems within the shoulder itself.
How Are Shoulder Problems Diagnosed?
As with any medical issue, a shoulder problem is generally
diagnosed using a three-part process:
- medical history – The patient
tells the doctor about any injury or other condition that
might be causing the pain.
- physical examination – The doctor
examines the patient to feel for injury and to discover
the limits of movement, location of pain, and extent of
joint instability.
- tests – The doctor may order one
or more of the tests listed below to make a specific diagnosis.
These tests may include the following:
- Standard x ray – a familiar procedure in
which low-level radiation is passed through the body
to produce a picture called a radiograph. An x ray
is useful for diagnosing fractures or other problems
of the bones. Soft tissues, such as muscles and tendons,
do not show up on x rays.
- Arthrogram – a diagnostic record that can
be seen on an x ray after injection of a contrast
fluid into the shoulder joint to outline structures
such as the rotator cuff. In disease or injury, this
contrast fluid may either leak into an area where
it does not belong, indicating a tear or opening,
or be blocked from entering an area where there normally
is an opening.
- Ultrasound – a noninvasive, patient-friendly
procedure in which a small, hand-held scanner is
placed on the skin of the shoulder. Just as ultrasound
waves can be used to visualize the fetus during pregnancy,
they can also be reflected off the rotator cuff and
other structures to form a high-quality image of
them. The accuracy of ultrasound for the rotator
cuff is particularly high.
- MRI (magnetic resonance imaging) – a noninvasive
procedure in which a machine with a strong magnet
passes a force through the body to produce a series
of cross-sectional images of the shoulder. Other
diagnostic tests, such as one that involves injecting
an anesthetic into and around the shoulder joint,
are discussed in detail in other parts of this booklet.
To read the rest of this excellent article on shoulder
problems, including diagnosing and treating specific
problems, produced by the National Institute of Arthritis
and Musculoskeletal and Skin Diseases, please click here: http://www.niams.nih.gov/Health_Info/Shoulder_Problems/default.asp
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