Diagnostic Ultrasonography

Ultrasound (US) is an excellent imaging modality to diagnose rotator cuff and biceps disorders, but it is by no means the perfect imaging modality for the shoulder. However, there are several other shoulder imaging modalities, such as magnetic resonance imaging (MRI), computed tomography (CT), and radiography. However, US affords several advantages over other modalities, such as MRI. First, it is cheaper to perform than an MRI and, therefore, it can help to ease the financial burden on the health care system. In the past, we would have also added that the money spent on a US can be earned by the practitioner performing the study. However, the reimbursement for diagnostic US has been drastically reduced over the past 3 years. Second, it is very sensitive and specific for diagnosing rotator cuff pathology and may be better than MRI to diagnose biceps pathology. This is partly due to the fact that the exam is dynamic and the patient's response to certain movements or palpation with the probe can provide real-time information that an MRI cannot. Third, patients tend to appreciate the immediate diagnosis and it forges a stronger bond between the physician and the patient. Fourth, it is very accessible because most machines are portable. Fifth, the machine can be used to guide therapeutic interventions, such as injections. Sixth, patients who are precluded from having an MRI due to claustrophobia, the presence of metal aneurysm clips or stents, or pacemakers, can have a US done without any risk. Seventh—similar to the latter point—metal implants at the site of surgery do not interfere as much with a US examination as with an MRI or CT scan, so US is an excellent modality to assess a postoperative rotator cuff repair.

However, there are a few disadvantages to using US. First, the power of diagnosis is operator dependent. It takes practice and experience to be able to use the machine. Second, it is not a good modality to view deep structures. For example, it is not as good as an MRI or an MR arthrogram to assess labral pathology. Third, it does require some time in clinic to set up and perform the US. This may not be feasible for an extremely busy practitioner.

Orthopedic surgeons have an advantage in using shoulder US over other subspecialties that manage shoulder pathology. We have arthroscopic surgery; other specialties, such as radiology, have access to imaging including radiographs, MRI, CT, and nuclear medicine imaging. Rheumatologists have these modalities in addition to physical examination and patient history. Orthopedic surgeons have access to all of the above and the most sensitive tool of all, direct visualization. As orthopedic surgeons, we have the opportunity to correlate imaging findings with actual clinical appearance at the time of arthroscopic surgery.

Basic Terminology

This is not a complete text on US, so we will not discuss the terminology in detail, but the reader should be able to understand the images based on their knowledge of anatomy. In order to make sense of US images and to convey findings, certain basic concepts or terms need to be defined. These terms allow the user to identify pathology as well as to convey objective findings to others regarding the pathology. These terms will be referred to throughout this chapter.

Axis defines the plane of view. Three-dimensional imaging, such as CT or MRI, can be divided into sagittal, coronal, and axial planes. These planes are referenced off of the central axis of the human body. US is live imaging, which can include oblique planes as well, and is referenced off the observed structure. By convention, structures are viewed by defined planes. In shoulder US, the two planes of view are longitudinal and transverse. The longitudinal plane refers to the long axis view of a given structure. For a biceps tendon, the long axis view is equivalent to a sagittal view ( Fig. 18.1 ). A long axis view of the supraspinatus is equivalent to a coronal oblique view ( Fig. 18.2A and B ). The transverse plane refers to the short axis view of a given structure. For a biceps tendon, the short axis view is equivalent to an axial view ( Fig. 18.3A and B ). A short axis view of the supraspinatus is equivalent to a sagittal oblique view ( Fig. 18.4A–C ).

Echogenicity refers to the capacity of a structure in the path of a US beam to reflect back sound waves. A hyperechoic structure shows a high reflective pattern and appears brighter than the surrounding tissue ( Fig. 18.5 ). An isoechoic structure demonstrates the same echogenicity as the surrounding soft tissues ( Fig. 18.6 ). A hypoechoic structure has a low reflective pattern and appears darker than the surrounding soft tissues ( Figs. 18.5 and 18.7 ). An anechoic structure does not reflect sound waves and is on a continuum, or represents an extreme case of a hypoechoic structure ( Figs. 18.7 and 18.8 ).

Anisotropy refers to a phenomenon in which certain highly organized structures appear hypoechoic if they are not viewed perpendicular to the US beam. For shoulder US, this most commonly occurs when viewing the biceps tendon. The probe is adjusted in an attempt to align it perpendicular to the structure to determine if the structure is truly hypoechoic or if it is anisotropic ( Figs. 18.9 and 18.10 ).