Traumatic Shoulder Instability.
Last updated Thursday, February 10, 2005
Figure 4 - Age at presentation of traumatic instability patients HistoryHow does traumatic shoulder instability usually begin? Traumatic instability commonly begins with an injury when the
patient is between 14 and 34 years of age. In suspected recurrent
instability from a traumatic cause, the most important element in the
history is the definition of the original injury. As is evident to
anyone who has attempted to recreate these lesions in a cadaver,
substantial force is required to produce a traumatic dislocation. In
characteristic anterior traumatic instability, the structure that is
avulsed is the strongest part of the shoulder's capsular mechanism: the
anterior inferior glenohumeral ligament. In order to tear this
ligament, substantial force needs to be applied to the shoulder when
the arm is in a position to tighten this ligament. Thus the usual
mechanism of injury involves the application of a large
extension-external rotation force to the arm elevated near the coronal
plane. Such a mechanism may occur in a fall while snow skiing or while
executing a high speed cut in water skiing, in an arm tackle during
football, with a block of a volleyball or basketball shot, or in
relatively violent industrial accidents with the arm in this position.
Awkward lifting and rear-end automobile accidents would not be expected
to provide the conditions or mechanism for this injury. We find that
direct questioning and persistence are often required to elicit a full
description of the initial mechanism of injury including the position
of the shoulder and the direction and magnitude of the applied force at
the time of the initial injury. Yet this information is critical to
establishing the diagnosis.
An initial traumatic dislocation often requires assistance in
reduction, rather than reducing spontaneously as is usually the case in
atraumatic instability. Radiographs from previous emergency room visits
may be available to show the shoulder in its dislocated position.
Axillary or other neuropathy may have accompanied the glenohumeral
dislocation. Any of these findings individually or in combination
support the diagnosis of traumatic as opposed to atraumatic
instability.
Traumatic instability may occur without a complete dislocation. In
this situation, the injury produces a traumatic lesion, but this lesion
is insufficient to allow the humeral head to completely escape from the
glenoid. The shoulder may be unstable because, as a result of the
injury, it manifests apprehension or subluxation when the arm is placed
near the position of injury. In these cases there is no history of the
need for reduction nor radiographs with the shoulder in the dislocated
position. Thus the diagnosis rests to an even greater extent on a
careful history that focuses on the position and forces involved in the
initial episode. How do recurrent episodes of shoulder instability affect traumatic shoulder instability? Characteristically, the shoulder with traumatic instability is
comfortable when troublesome positions are avoided. However, the
shoulder often remains vulnerable to recurrent episodes of instability.
These may range from sensations of apprehension or impending
dislocation to recurrent complete dislocations requiring manipulative
reduction. In this context, recurrent episodes of instability occur
most commonly when the shoulder is forced unexpectedly into the
abducted externally rotated position or during sleep when the patient's
active guard is less effective. There may be a history of increasing
ease of dislocation. We determine whether the patient is reluctant to
carry out certain activities or to put the arm in certain positions
because of fear of instability. This apprehension may interfere with
the patient's ability to use the arm for work, activities of daily
living, or sports.
The history must seek to demonstrate the position and forces
involved in the initial and subsequent episodes of instability. The
examiner must be convinced that these are appropriate and sufficient to
tear the normally strong capsuloligamentous structures which stabilize
the shoulder at the extremes of motion. This careful history is the
foundation on which the diagnosis of traumatic instability rests.
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