US of the shoulder: non-rotator cuff disorders.
The most common indication for shoulder ultrasonography (US) is the diagnosis of rotator cuff disease. However, there is a spectrum of non-rotator cuff abnormalities that are amenable to US examination, including instability of the biceps tendon, glenohumeral joint, and acromioclavicular joint; arthropathies and bursites (inflammatory diseases, degenerative and infiltrative disorders, infections); nerve entrapment syndromes; and space-occupying lesions. Many of these conditions may be overlooked clinically or can even mimic rotator cuff tears, and US can help redirect the diagnosis if a complete shoulder examination rather than a simple rotator cuff assessment is performed. In addition, US can be remarkably helpful in guiding either needle aspiration procedures or local injection therapy in patients with synovial processes. Although radiography, magnetic resonance (MR) imaging, and computed tomographic and MR arthrography are effective modalities for the evaluation of non-rotator cuff disorders, US is both less costly and less invasive and will likely be used more frequently in this setting as experience increases. Once adequate radiographs have been obtained to exclude apparent bone disorders, high-resolution US should be the first-line imaging modality in the assessment of non-rotator cuff disorders of the shoulder, assuming the study is performed with high-end equipment by an experienced examiner.