Atraumatic Shoulder Instability.
Last updated Thursday, February 10, 2005
ExaminationPhysical examination The physical examination of patients with AMBRII syndrome is usually
started by asking them to demonstrate the positions in which the
shoulder feels unstable. They may demonstrate a spontaneous jerk test
by bringing the elevated arm horizontally across the chest, causing the
humeral head to subluxate posteriorly. Then by returning the elevated
humerus to the coronal plane they produce a "clunk" on reduction of
glenohumeral joint (much like the Ortolani and Barlow signs of the
hip). Using the palpable scapular coordinates, we can estimate the
scapular plane in which the shoulder subluxes and the plane in which it
reduces. Patients may also demonstrate that when they attempt to lift
an object or tie their shoes, the shoulder subluxates inferiorly. They
may demonstrate that when they lie on the affected shoulder it is
pushed forward out of joint. Finally, they may demonstrate by elevating
the arm in a posterior humerothoracic plane that they can produce
anterior subluxation with spontaneous reduction on return to the
coronal plane. By allowing the patient to demonstrate the symptomatic
positions and motions of instability, our hands are free to define the
humeroscapular positions at the moments of interest. These observations
may reveal faulty patterns of scapulohumeral mechanics, such as
allowing the lateral scapula to droop during lifting or retracting the
scapula during anterior elevation of the humerus.
We have described our investigations of classic clinical laxity
tests showing that, in a small group of subjects, the magnitude of
translation for shoulders with atraumatic instability is essentially
the same as that of normal shoulders or shoulders with traumatic
instability. Therefore, we pay particular attention to the patient's
response during laxity testing: we are seeking to reproduce the
translations which duplicate the symptoms that brought the patient in
for treatment. Our best diagnostic confirmation occurs when, during a
laxity test, the patient states "that's it, that's the thing that's
bothering me." We refer to this as recognition of the symptomatic event
when it is reproduced during the examination.
We always make a point of examining the laxity of the contralateral
glenohumeral joint. Occasionally, laxity tests will yield different
results on the symptomatic side. More often, however, examination of
the contralateral shoulder is similar to the symptomatic one. This
allows us the opportunity to demonstrate to the patient and the family
that, while both shoulders demonstrate similar degrees of laxity, the
patient is able to control one of them using good mechanics. This
demonstration helps set the foundation for our discussion of the need
to regain stabilizing neuromuscular control of the symptomatic
shoulder.
Finally, we examine the strength of abduction and rotation to gauge
the power of the muscles contributing to stability through concavity
compression. We also examine the strength of the scapular protractors
and elevators which are necessary to position the scapula securely. Radiographs In atraumatic instability shoulder radiographs characteristically
show no bony pathology. Because these patients characteristically
demonstrate midrange instability, radiographs may show translation of
the humeral head with respect to the glenoid. 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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