The initial episode
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.
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.
Evaluation and examination
The goal of the physical examination is largely to confirm the impression obtained from the history: that a certain combination of arm position and force application produces the actual or threatened glenohumeral instability that is of functional concern to the patient. If the diagnosis has been rigorously established from the history, for example by documented recurrent anterior dislocations, it is not necessary to risk redislocation on the physical examination. If such rigorous documentation is not available, however, we must challenge the ligamentous stability of the shoulder in the suspected position of vulnerability. We seek to have the patient identify the positions and events that are of functional significance.
The most common direction of recurrent traumatic instability is anteroinferior. Stability in this position is challenged by externally rotating and extending the arm elevated in the coronal plane. This is conveniently done in the supine position with one of the examiner's hands under the back of the shoulder serving as a fulcrum for the external rotation and extension force. We apply extension and external rotation loads in different positions of elevation to challenge the various parts of the anterior capsular mechanism. The patient will very often guard against the position of instability by actively limiting the range of humeroscapular motion. For this reason, we may need to hold the arm in the challenging position for 1 to 2 minutes to fatigue the stabilizing musculature. When the muscle stabilizers tire, the capsuloligamentous mechanism is all that is holding the humeral head in the glenoid. At this moment the patient with traumatic anterior instability becomes apprehensive, recognizing that the shoulder is about to come out of joint. This recognition is strongly supportive of the diagnosis of traumatic anterior instability.
Standard tests of glenohumeral laxity are of limited value in the diagnosis of traumatic instability. As has been described earlier the magnitude of translation on the standard test of glenohumeral laxity does not distinguish stable from unstable shoulders. The magnitude of translation on some clinically stable shoulders may be as great or greater than that on shoulders with traumatic instability. However, the experienced examiner may detect certain findings such as increased ease of translation on the anterior drawer test or grinding as the humeral head slides over a bony edge of the glenoid from which the labrum has been avulsed. There may also be a catching or a locking of a torn glenoid labrum, producing findings analogous to those of a torn meniscus in the knee.
We do not consider pain on abduction, external rotation and extension to be specific for instability. Such pain may relate to shoulder stiffness or alternatively to abutment of the glenoid against the cuff insertion to the head posteriorly. Furthermore, relief of this pain by anterior pressure on the humeral head may result from diminished stretch on the anterior capsule or from relief of the abutment posteriorly.
|In all patients with traumatic instability but particularly in those over age 35, the strength of the internal and external rotation must be examined. With increasing age, there is an increasingly common association between traumatic glenohumeral instability and rotator cuff defects. Patients with significant cuff lesions may demonstrate atrophy of the spinatus muscles as well as pain and or weakness on resisted abduction or external rotation. Any rotator cuff pathology must be recognized and incorporated in the treatment plan.
Finally, carefully examine the brachial plexus to assure that the episodes of traumatic instability have not compromised its function.
Radiographs frequently help to provide confirmation of traumatic glenohumeral instability. These findings may include an indentation or impaction in the posterior aspect of the humeral head from contact with the anteroinferior corner of the glenoid when the joint is dislocated. Radiographs may also reveal a periosteal reaction to the ligamentous avulsion at the glenoid lip or occasionally a fracture of the glenoid rim.
These lesions are usually revealed by an anteroposterior view in the plane of the scapula, a proper axillary view, and an apical oblique view, as shown in the example movie listed below. We have not found additional radiographic views, CT arthrography, or MRI to be cost effective in the evaluation of shoulders with characteristic traumatic instability. We occasionally use CT to define the magnitude of bone loss when a sizable humeral head or glenoid defects have been identified on a series of plain radiographs.
In a patient whose onset of traumatic instability occurred after age 35 there may be evidence on history and physical examination of rotator cuff pathology. In these situations, preoperative imaging of cuff integrity may play an important role in surgical planning: the approach for rotator cuff repair is quite different than the approach for the repair of an anterior inferior capsular lesion.
Electromyography may be helpful in the evaluation of the patient with recurrent traumatic instability if the history and physical examination suggest residual brachial plexus lesions.
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A patient with traumatic anterior glenohumeral instability has symptoms of instability (apprehension, subluxation, or dislocation) when the arm is elevated near the coronal plane, extended, and externally rotated. Characteristically the shoulder is relatively asymptomatic in other extreme positions or in midrange positions.
Thus, for some patients appropriate management may consist solely of education about the nature of the lesion and identification of the positions and activities that need to be avoided. Strengthening the shoulder musculature may help prevent the shoulder being forced into positions of instability. The exercise program suggested for atraumatic instability may be considered as an option for traumatic instability as well. "Training tape" may be applied to the anterior aspect of the shoulder as a reminder to avoid abduction, external rotation, and extension ofthe shoulder. However, many patients with refractory symptoms will wish to consider surgical repair.