Evaluation of Recurrent Instability.
Last updated Friday, November 16, 2007
The physical examination (atraumatic)Demonstration of instability The patient is routinely asked if he or she can dislocate the
shoulder at will. This enables the surgeon to see the different
positions of concern and directions of translation. By palpating the
scapula, the surgeon can estimate the relative position of the humerus
and scapula when the shoulder is translated and reduced. There are
three common demonstrations of instability:
- The patient may demonstrate a spontaneous
"jerk" test by bringing the internally rotated arm horizontally across
the chest, causing the humeral head to subluxate posteriorly. Then by
returning the elevated humerus to the coronal plane the shoulder
produces a "clunk" on reduction of glenohumeral joint (much like the
Ortolani and Barlow signs of the hip).
- The patient may demonstrate that when he or she attempts to lift an object or tie a shoe, the shoulder subluxates inferiorly.
- The
patient may demonstrate that the shoulder translates when the arm is
elevated in posterior humerothoracic planes with spontaneous reduction
on return to the coronal plane.
Laxity tests These tests examine the amount of translation allowed by the
shoulder starting from positions where the ligaments are normally
loose. The amount of translation on laxity testing is determined by the
length of the capsule and ligaments as well as by the starting position
(i.e. more anterior laxity will be noted if the arm is examined in
internal rotation--which relaxes the anterior structures, than if it is
examined in external rotation--which tightens the anterior structures).
In interpreting the significance of the degree of translation on
laxity tests, it is important to use the contralateral shoulder as an
example of what is "normal" for the patient. Not infrequently the
laxity on the symptomatic side will be similar to that on the
asymptomatic side. Investigations of clinical laxity tests showed that
the range of translations for shoulders with atraumatic instability was
similar to that of normal shoulders or shoulders with traumatic
instability (see figure 5). (Harryman, Sidles and Matsen, 1992)
However, a distinguishing feature of many shoulders with atraumatic
instability is that the resistance to translation is diminished when
the humeral head is pressed into the glenoid fossa; suggesting that the
effective glenoid concavity is diminished. It is helpful if the patient
recognizes one or more of the directions of translation as being
responsible for his or her clinical symptoms. Finally, it is important
to point out that these are tests of laxity, not tests for instability:
Many normally stable shoulders, such as those of gymnasts, will
demonstrate substantial translation on these laxity tests even though
they are asymptomatic.
Drawer test
The patient is seated with the forearm resting on the lap and the
shoulder relaxed. The examiner stands behind the patient. One of the
examiner's hands stabilizes the shoulder girdle (scapula and clavicle)
while the other grasps the proximal humerus. These tests are performed
with (1) a minimal compressive load (just enough to center the head in
the glenoid) and (2) with a substantial compressive load (to gain a
feeling for the effectiveness of the glenoid concavity). Starting from
the centered position with a minimal compressive load, the humerus is
first pushed forward to determine the amount of anterior displacement
relative to the scapula. The anterior translation of a normal shoulder
reaches a firm end-point with no clunking, no pain and no apprehension.
A clunk or snap on anterior subluxation or reduction may suggest a
labral tear or Bankart lesion. The test is then repeated with a
substantial compressive load applied before translation is attempted to
gain an appreciation of the competency of the anterior glenoid lip. The
humerus is returned to the neutral position and the posterior drawer
test is performed, with light and again with substantial compressive
loads to judge the amount of translation and the effectiveness of the
posterior glenoid lip, respectively. (Silliman and Hawkins, 1993)
Sulcus test
The patient sits with the arm relaxed at the side. The examiner
centers the head with a mild compressive load and then pulls the arm
downward. Inferior laxity is demonstrated if a sulcus or hollow appears
inferior to the acromion. Competency of the inferior glenoid lip is
demonstrated by pressing the humeral head into the glenoid while
inferior traction is applied.
Push-pull test
The patient lies supine with the shoulder off the edge of the table.
The arm is in 90 degrees of abduction and 30 degrees of flexion.
Standing next to the patient's hip, the examiner pulls up on the wrist
with one hand while pushing down on the proximal humerus with the
other. The shoulders of normal, relaxed patients often will allow 50
per cent posterior translation on this test.
Stability tests These tests examine the ability of the shoulder to resist challenges
to stability in positions where the ligaments are normally under
tension.
Fulcrum test
The patient lies supine at the edge of the examination table with
the arm abducted to 90 degrees. The examiner places one hand on the
table under the glenohumeral joint to act as a fulcrum. The arm is
gently and progressively extended and externally rotated over this
fulcrum. Maintaining gentle passive external rotation for a minute
fatigues the subscapularis, challenging the capsular contribution to
the anterior stability of the shoulder. The patient with anterior
instability will usually become apprehensive as this maneuver is
carried out (watch the eyebrows for a clue that the shoulder is getting
ready to dislocate). In this test, normally no translation occurs
because it is performed in a position where the anterior ligaments are
placed under tension.
Crank or apprehension test
The patient sits with the back toward the examiner. The arm is held
in 90 degrees of abduction and external rotation. The examiner pulls
back on the patient's wrist with one hand while stabilizing the back of
the shoulder with the other. The patient with anterior instability
usually will become apprehensive with this maneuver. As for the fulcrum
test, no translation is expected in the normal shoulder because this
test is performed in a position where the anterior ligaments are placed
under tension.
Jerk test
The patient sits with the arm internally rotated and flexed forward
to 90 degrees. The examiner grasps the elbow and axially loads the
humerus in a proximal direction. While axial loading of the humerus is
maintained, the arm is moved horizontally across the body. A positive
test is indicated by a sudden jerk as the humeral head slides off the
back of the glenoid. When the arm is returned to the original position
of 90-degree abduction, a second jerk may be observed, that of the
humeral head returning to the glenoid.
Strength tests The strength of abduction and rotation are tested to gauge the power of
the muscles contributing to stability through concavity compression.
The strength of the scapular protractors and elevators are also tested
to determine their ability to position the scapula securely.Radiographs In atraumatic instability shoulder radiographs characteristically
show no bony pathology. Specifically, there is no posterolateral
humeral head defect, no glenoid rim fracture or new bone formation and
no evidence of tuberosity fracture. Because these patients
characteristically demonstrate midrange instability, radiographs may
show translation of the humeral head with respect to the glenoid; for
example, the axillary view may show posterior subluxation.
Occasionally, radiographs may suggest factors underlying the atraumatic
instability such as a relatively small or hypoplastic glenoid or a
posteriorly inclined or otherwise dysplastic glenoid. The bony glenoid
fossa may appear quite flat; however, it is difficult to relate the
apparent depth of the bony socket to the effective depth of the fossa
formed by cartilage and labrum covering the bone.
We do not use stress radiographs, arthrography, MRI, or arthroscopy in the diagnosis of atraumatic instability.
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