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Shoulder Instability
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The shoulder joint has
been described as a ball-and-saucer joint. Consequently, there is little
stability imparted by the bony architecture. In order to maintain that
consistent ball-and-saucer relationship (keep the ball from rolling off the
saucer), ligaments are present that connect the ball (head of the humerus, or
arm bone) directly to the saucer (glenoid process of the scapula, or shoulder
blade). These ligaments allow some motion between these two structures, but
limit the motion in order to prevent dislocation. Also, the muscles around the shoulder help to control
this ball-and-saucer movement. These act in concert with the ligaments in
order to allow smooth, pain-free, and stable motion of this important joint. |
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Traumatic
dislocations, such as that during a tackle in football, invariably tear some
of the stabilizing ligaments. Although the ligaments heal, they often heal looser
than what they originally were. The loose ligaments do not provide as much
stability as they did prior to injury. This increases the risk of having a
further dislocations. With each subsequent re-dislocation, the ligaments are
again injured and progressively get even looser. This can progress to the
point where the dislocation happens from very trivial activities. At this
stage, the only effective treatment is to surgically repair the torn ligaments
in order to tighten them and prevent abnormal motion of this ball-and-saucer
joint. |
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Sometimes the
instability is not severe enough to allow a dislocation, but enough to allow
the ball to move part way off the saucer. This is referred to as a
subluxation. This can be thought of as a partial dislocation in that the ball
and saucer are still touching, but the ball has moved off the center of the
saucer. This abnormal position can cause discomfort. Because the amount that
the ball has to move is less than in a complete dislocation, the amount that
the ligaments have to be stretched is also less. This lesser degree of
instability can therefore often be controlled by strengthening the muscles
around the shoulder to help reduce some of the stress of stabilizing the joint
from the ligaments. Therefore, these shoulders,
although somewhat loose, can often be treated successfully without having to
surgically tighten the ligaments. |
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