Anterior shoulder subluxation is a transitory event that can be difficult to define. Descriptive phrases in sports, such as the so-called dead-arm syndrome, reflect on the associated neurological symptoms that may occur with excessive anterior humeral translation. The military is a unique setting in which to study this disorder, since it provides information on young active individuals who must perform at a high level and comply with medical advice. Short-term and midterm data collection and repetitive examinations are routinely available. Most studies have examined dislocation events, since the pathologic event was documented by radiographs and/or there was required assistance for reduction1,2. This unique study on subluxation suggests that articular injury may explain why certain patients have recurrences or progress from subluxation to dislocation.
It is important to acknowledge that this is a study of disorders with a traumatic etiology. Shoulders with increased laxity that have a momentary subluxation due to position or strain are not included in this population. We may expect to find an absence of labral injury in patients with subluxation but with no history of trauma.
The authors identified a paucity of findings on radiographs. In contrast, magnetic resonance imaging demonstrated that twenty-six of twenty-seven patients had pathologic findings along the anterior margin of the glenoid or labrum. Hill-Sachs lesions of the humeral head were more consistent with a bone bruise than with an actual deformity, which suggests a different pathologic setting than that of dislocation with a "locked" dissociation of the glenohumeral joint.
Owens et al. introduced the term transient luxation, which is defined by traumatic etiology, magnetic resonance imaging findings, and anticipated arthroscopic findings that may impact the prognosis with regard to recurrence.
The surgical findings in this study of patients with traumatic subluxation included "an essential lesion" in a high percentage of patients. A Bankart lesion was revealed in 96% of patients with a single injury. A Hill-Sachs lesion of the humeral head, in contrast, was less identifiable on arthroscopic examination than on magnetic resonance imaging. These findings would suggest evidence of excessive anterior translation prior to dislocation. Similar to what has been found with regard to knee subluxation in patients with anterior cruciate ligament tears, the magnetic resonance imaging findings in patients with glenohumeral subluxation may represent a bone bruise rather than an impaction fracture. Magnetic resonance imaging is the diagnostic modality of choice in patients with a history and physical findings that would support the diagnosis of subluxation.
Treatment options for subluxation have traditionally been nonoperative, with successful outcomes anticipated. This may be due to the multiple settings, including increased joint laxity with minor trauma, overhead pitchers with so-called dead-arm syndrome, and traumatic momentary subluxations. Patients with traumatic-onset transient luxation may be considered for early surgical stabilization3. There would be at least two reasons to consider arthroscopic stabilization in these high-risk patients: (1) Approximately one-quarter of the patients who elected to have nonoperative treatment had recurrent subluxation. Multiple articular events would be expected to extend the articular injury4. Although this percentage of recurrence is less than that in patients with actual glenohumeral dislocation, the overall risk cannot be calculated, since half of the patients elected to have surgical stabilization and did not have an opportunity to have recurrences. (2) Another reason to consider early stabilization is to minimize risk of interrupted athletic seasons. It is not uncommon for athletes to experience an initial subluxation event and then return to athletic competition after a period of rest and rehabilitation. Additional injury after this initial subluxation can cause dislocation and interruption of a subsequent athletic season. The overall risk factors for recurrence may be similar to those for a shoulder with an initial dislocation in terms of age, type of sport or activity, and pathologic findings. The advantages of early arthroscopic treatment include ease of arthroscopic evaluation and clear visualization of the articular disorder following trauma. Considering that arthroscopic evaluation and treatment provides an opportunity for an anatomic repair of the detached labrum or glenoid rim, one would expect a high percentage of excellent outcomes with a minor risk of recurrence, complication, or the development of degenerative arthritis.
To conclude, glenohumeral subluxation following a traumatic event can produce articular findings similar to the "essential lesion" of a recurrent shoulder dislocation. Radiographs do not demonstrate findings in most of these cases. Magnetic resonance imaging is a preferred study to identify anterior glenoid rim and labral injury but may exaggerate articular cartilage findings in the humeral head. Arthroscopy can confirm injury to the anterior aspect of the glenoid following initial subluxation, but it cannot confirm articular injury to the posterior aspect of the humeral head. In the series by Owens et al., the patients with positive findings on magnetic resonance imaging can be subclassified as patients who have had a transient subluxation. The athletes should be informed of the increased risk of recurrent subluxation and potentially a dislocated shoulder5. After receiving this information, the patient may decide to undergo early arthroscopic repair of the anterior glenolabral structures. Because subluxation causes minimal articular cartilage changes to the humeral head, one would expect maintenance of maximal external rotation when the athlete returns to activities.