Assessment of deltoid reinnervation following brachial plexus injury remains a clinical
challenge. Traditional tests, such as the Bertelli abduction-in-internal-rotation
test, may yield false-negative results due to compensatory activation of adjacent
muscles. Concomitant rotator cuff dysfunction may interfere with testing. Electromyography
(EMG) has not proved to be efficient to document early signs of reinnervation of the
posterior fibers of the deltoid.
We describe a straightforward clinical test that allows the examiner to isolate and
confirm voluntary contraction of the posterior deltoid. This test has been applied
consistently over years of clinical follow-up and is applicable in cases of nerve
grafting, nerve transfers, or spontaneous reinnervation of the axillary nerve.
Materials and Methods
The patient is examined while upright (sitting or standing). The arm rests on a flat
platform at 90 degrees abduction in the coronal plane. He/she is asked to lift the
elbow off the platform. The examiner, standing behind the patient, then observes for
contraction of the deltoid.
A positive test is defined by visible contraction of the posterior deltoid fibers
([Videos 1] and [2]). Notably, no resistance is applied. The test is applicable irrespective of the
reconstructive technique used (nerve grafts, transfers, or conservative observation).
Video 1 Video of a normal individual showing isolated contraction of the deltoid.
Video 2 Contraction of posterior fibers of the deltoid indicating early re-innervation.
Discussion
Evaluation of the function of the deltoid is challenging. Attempted abduction inevitably
involves use of the rotator cuff. Bertelli's test has proved useful in detecting isolated
deltoid deficit in the presence of an intact rotator cuff. However, there are clinical
situations where the test has not proved useful in guiding clinical strategy. For
instance, infraclavicular brachial plexus injuries following trivial trauma often
present with axillary nerve injuries. In such cases, the impact is at a low velocity
and spontaneous recovery is anticipated. However, abduction in internal rotation cannot
be administered because of the rotator cuff weakness. The axillary nerve enters the
deltoid from the posterior margin and those fibers will contract first ([Fig. 1]). This test has proved uniformly successful in detecting the contraction of the
deltoid so that further recovery can be expected and unnecessary nerve transfers can
be avoided. Similarly, detection of this reinnervation on an EMG will also involve
specific activation of the deltoid when the needle is inserted. So this report can
also serve as a guideline for more accurate electrodiagnostic evaluation in such patients.
This test addresses key limitations in the clinical evaluation of shoulder abduction
following brachial plexus injury. By requiring only conscious activation of the posterior
deltoid at 90-degree abduction, it isolates the muscle effectively without requiring
full limb elevation or rotator cuff support. Thus, reinnervation of the deltoid following
a nerve transfer or grafting procedure can be demonstrated. If a mirror is employed,
it serves as a biofeedback device to encourage strengthening of the deltoid.
Limitations include the absence of interobserver validation and formal quantification
of sensitivity/specificity.
Conclusion
This maneuver provides a fast, reliable, and specific method to confirm isolated posterior
deltoid reinnervation across a wide range of brachial plexus reconstructive strategies.
It should be considered a valuable addition to both clinical evaluation and electromyographic
assessment of deltoid function.
Fig. 1 The axillary nerve traverses the quadrangular space and enters the deltoid muscle
from the back innervating the posterior fibers first.
