Patients with MDI may report recurrent subluxations with minimal trauma and a sense of instability rather than frank dislocations that require reduction. While occasionally caused by a single large traumatic event, most MDI patients do not present with a high-energy dislocation. When dislocations do occur, they usually require minimal force and frequently spontaneously reduce. Patients may not describe individual episodes of subluxation and may instead complain of a "dead arm" or pain after episodes of physical activity.17 Some authors report that patients typically are symptomatic in the midrange positions of gleno-humeral motion and can be symptomatic during activities of daily living.1 It is particularly important to obtain information about the activities and arm positions that are associated with symptoms. This may provide clues to the direction of instability. An important part of the initial patient evaluation involves recognizing the voluntary dislocating patient. This subgroup of patients frequently has secondary gain issues and will not be compliant with treatment regimens.6
The physical examination of the patient must elicit nonvoli-tional glenohumeral translation that reproduces the patient's symptoms.6 Again, the key factor is to separate asymptomatic joint laxity from symptomatic instability. It is critical to examine the asymptomatic shoulder to establish a baseline understanding of the patient's natural laxity. However, it is not uncommon to note bilateral symptoms in patients with MDI.
Neer and Foster hypothesized that a patulous inferior capsule was the cardinal lesion in the MDI shoulder.2 Inferior laxity must be assessed by applying inferior traction to the adducted arm in a bid to cause inferior humeral migration. If inferior translation of 1 to 2 cm occurs with the appearance of skin indentation under the acromion (sulcus sign), the patient is thought to have inferior capsular laxity, an important component of MDI (see Fig. 20-1).2 Inferior laxity may also be evaluated by abducting the arm 90 degrees and directing an inferior force on the proximal humerus in an effort to promote excessive inferior translation.13 A careful examination of anterior and posterior glenohumeral stability should also be performed. Multiple maneuvers exist that can help define anterior and posterior laxity, including the apprehension-relocation test, the load and shift test, and the push-pull test.
Plain radiographs are typically normal in patients with MDI. In patients with a documented traumatic dislocation superimposed on the clinical setting of MDI, a humeral head defect (Hill-Sachs lesion) or glenoid injury may be noted. Mag-
Figure 20-2 Contrast-enhanced magnetic resonance coronal image of a patient with symptomatic multidirectional instability. Contrast distends the voluminous capsule (arrow). Frequently, this is the only pathologic radiographic finding in patients with multidirectional instability.
Figure 20-1 The sulcus sign. Traction on the adducted arm produces a conspicuous sulcus (arrow) between the acromion and humeral head. This is a classic physical examination finding in multidirectional instability.
Figure 20-3 Open capsular shift. A, The subscapularis is incised to expose the anterior capsule. B, A laterally based T-capsulotomy produces superior and inferior capsular flaps. C, After the inferior flap is released from the humeral neck, it is advanced superior to reduce the volume of the axillary pouch and tighten the inferior and middle glenohumeral ligaments. (From Hawkins RJ, Bell RH, Lippitt SB: Instability. In Hawkins RJ, Bell RH, Lippitt SB [eds]: Atlas of Shoulder Surgery. Philadelphia, Mosby, 1996, pp 65-67.)
netic resonance imaging may also be noncontributory in the diagnosis of MDI. However, contrast-enhanced magnetic resonance imaging may reveal a voluminous capsule or labral injury (Fig. 20-2).
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