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Shoulder Instability
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What is shoulder instability?
Shoulder instability is the inability of the shoulder
joint to stay in place during normal use of the shoulder. Although dislocation of
the shoulder is the ultimate example of instability, there are many other types
of instability.
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The ball and socket are completely separated in a shoulder dislocation.
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Subluxation is a term used to describe a partial dislocation. When the humeral head
slides part of the way out of joint, it is a subluxation.
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In a normal shoulder, the forces across
the joints are centered.
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In an unstable joint, the forces are off center and can cause premature wear
of the joint, leading to arthritis.
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Some patients have ligaments and joint capsules throughout their bodies that are
more flexible than others. These patients are frequently perceived as being ‘double-jointed’.
When this extra motion takes place in the shoulder and causes problems, it is likely
that subluxation of the shoulder has occurred. Frequently, a simple activity such
as throwing a ball or serving in tennis can cause pain in these patients. The pain
on extreme motion can be an indicator of subtle instability.
Traumatic dislocation of the shoulder is a different type of shoulder problem than
hyperlaxity (being double-jointed). Initial shoulder dislocations are usually due
to a violent force applied to the shoulder forcing it out of joint. When this occurs,
the restraining ligaments that support the joint are torn. Sometimes, small fractures
and rotator cuff tears can occur as well.
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Collisions during football are a common cause of shoulder dislocations.
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The humeral head (ball) is forced out of the glenoid (socket) causing damage
to ligaments.
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How is an unstable shoulder
diagnosed?
When the ligaments that prevent dislocation in a normal shoulder are torn
during a dislocation, the majority of the time they do not heal in the right position.
This can lead to involuntary dislocation of the shoulder. Patients can dislocate
in their sleep, while working, or during simple activities such as combing hair-
frequently requiring a visit to the emergency room to reduce the dislocation.
When the ligaments are not torn, but stretched as in a subluxing shoulder, the diagnosis
can be difficult. Many patients who have a subluxing shoulder do not know what is
occurring in their shoulder when it is painful. A careful history and physical examination
is the key to diagnosis of subtle instability. Sometimes, an MRI or Arthrogram (an
x-ray test involving dye injection into the shoulder) can be useful to demonstrate
the torn ligaments.
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How is shoulder instability
treated?
Treatment for shoulder instability is based on many factors. The activity
level of the patient, the anatomic changes associated with the specific type of
instability, and the frequency of the symptoms are crucial parts of the criteria
for non-surgical vs. surgical treatment.
The treatment for instability is highly individualized. Strengthening of the muscles
surrounding the rotator cuff and the shoulder girdle itself is a crucial part of
treatment for shoulder instability. However, should non-surgical treatment fail
to improve the patient’s symptoms operative intervention may be indicated.
Operative treatment of shoulder instability is directed at the specific anatomic
alterations that occur when the shoulder is unstable. Bone and soft tissue alterations
are addressed either via an arthroscopic or traditional open procedures when instability
is treated surgically.
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