Neuromuscular ultrasound application to the electrodiagnostic evaluation of quadrilateral space syndrome

Quadrilateral space syndrome (QSS) is a rare neurovascular compression syndrome that results from the compression of the axillary nerve and posterior circumflex humeral artery in the quadrilateral space. Electromyography often is used to evaluate for the presence of neuropathic changes in the deltoid and teres minor in cases of suspected QSS. Needle examination of the teres minor may be challenging because of the muscle's small size and proximity to the infraspinatus. In cases in which patients are overweight or have significant teres minor atrophy, localization of the muscle through conventional methods may be extremely difficult. We present a case of an overweight man with posterior shoulder pain who was diagnosed with QSS via the use of a combination of ultrasound and electromyography.