test unreliable. Second, as anterior instability is normally a problem with the inferior glenohumeral ligament, it would make sense that the most useful portion of the test would be done at 90 degrees of abduction. Unfortunately, achieving this position requires that one of the examiner's hands hold the patient's arm there, which then prevents it from being used to stabilize the scapula. Thus, the mobility of the scapula on the thorax decreases the sensitivity of the test. Finally, although the load and shift test can be learned to detect subtle differences in side-to-side laxity, we do not treat laxity. As stated before, laxity is a clinical sign and instability is a symptom.
The workhorse test for posterior instability is the push-pull test (Fig. 16-27). This is performed in the supine patient by holding the patient's arm at the wrist at 90 degrees abduction and neutral rotation.5,9 The examiner places the other hand on the proximal humerus and, while pulling with the arm holding the patient's wrist, pushes with the arm on the proximal humerus. This is often enough to maximally translate the patient's humeral head posteriorly. Again, the test is positive only when the maneuver reproduces the patient's symptoms, and in our experience, the patient's response to this test is not subtle. The only caution here is to be sure to differentiate between pain and instability because we have found the former to be consistently present with posterosuperior labral tears.
Jahnke or "Jerk" Test This test is performed in the seated or supine patient by placing the affected arm in maximal horizontal adduction with internal rotation.5,9 A posterior force is then applied (Fig. 16-28). In the patient with posterior instability, this starting position will sublux or dislocate the shoulder posteriorly, and care is taken to ask the patient whether this maneuver reproduces specific symptoms. Next, the shoulder is brought back from horizontal adduction while maintaining the posterior force on the humerus at the elbow. As the shoulder approaches normal, a clunk may herald the reduction of the subluxed shoulder, which is a positive test. In our experience, this test has few false-positive results and therefore has a good positive predictive value.
Tests for Multidirectional Instability
As patients with MDI often present with a chief complaint of pain, we believe that such tests are more appropriately discussed
Figure 16-27 Push-pull test.
Figure 16-28 A and B, Jahnke (jerk) test.
Figure 16-28 A and B, Jahnke (jerk) test.
in the preceding section. However, there are complementary data that should be included in the evaluation of the patient with MDI. The classic finding associated with MDI is a positive sulcus sign (see Fig. 16-18). This is a visible dimpling between the bottom of the acromion and the top of the humeral head when an inferior traction force is placed on the arm. This is quantified by measuring this acromiohumeral distance in millimeters. It should be remembered that the normal shoulder sits approximately 7 to 8 mm below the acromion, so that an acromio-humeral distance of 1.5 cm is really only 7 to 8 mm of excursion. It is again emphasized that instability implies symptoms and that a positive sulcus sign is not enough to make the diagnosis. Nevertheless, it is an important adjunctive clue for the diagnosis, and when positive, attempts should be made to correlate it with symptoms. When instability is the underlying diagnosis in MDI, patients often will complain that their shoulder comes "out the bottom," and we therefore ask patients this specific question if we are concerned that MDI is the underlying diagnosis.
There are other clues and complexes to note when entertaining the diagnosis of MDI. Many of these patients have generalized ligamentous laxity, which can be measured with such tests as an ability to touch the thumb to the forearm5,9,23 and hyperextension of the elbow or knee. These patients often will have reproduction of their symptoms in all directions of trans-lational testing and can be difficult to manage conservatively or operatively. Often patients with MDI will demonstrate a sulcus sign, in which downward traction on the humerus will produce a noticeable dimpling between the top of the humerus and bottom of the acromion and will demonstrate laxity in the anterior and posterior directions.
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