Traumatic Shoulder Instability.

Figure 4 - Age at presentation of traumatic instability patients

History

How 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.

How useful was this page or article? This article is rated out of 5 stars (65 ratings). Not useful at all Not very useful Useful Very useful Extremely useful