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field of view, making it inappropriate for a survey examination (eg, for ankle pain, knee pain, hip pain).4 Unlike CT and MRI, ultrasonography does not provide a “bird’s-eye view,” and important abnormalities can be missed during evaluation of large areas (Figure 4). Ultrasonography also cannot evaluate bone or intra-articular structures such as cartilage, bone marrow, labrum, and intra-articular ligaments; MRI is the standard for evaluating these structures.21 Ultrasonography is time-consuming. To perform a detailed examination of the anterior, posterior, medial, and lateral aspects of the hip, knee, or ankle would require 1.5 to 2 hours of scanning time and an additional 10 to 25 minutes of image checking and interpretation. ■ CURRENT CLINICAL INDICATIONS Musculoskeletal ultrasonography is best used for clinical questions regarding limited, superficial musculoskeletal problems. Real-time dynamic examinations are possible with ultrasonography Figure 4. Musculoskeletal ultrasonography is inappropriate for evaluating large areas. Here, ultrasonography did not fully demonstrate the extent or nature of the abnormality within the adductor musculature of the patient’s thigh (A, arrow). MRI demonstrated multiple large enhancing metastatic intramuscular masses (B, arrows). CONTINUED ON PAGE 296 Downloaded from www.ccjm.org on August 19, 2022. For personal use only. All other uses require permission. 296 CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 85 • NUMBER 4 APRIL 2018 MUSCULOSKELETAL ULTRASOUND Fluid collections Ultrasonography can help evaluate small fluid collections in soft tissue. As is true for a lung opacity on chest radiography, soft-tissue fluid detected on ultrasonography is nonspecific, and results must be correlated with the clinical picture to narrow the differential diagnosis. Fluid collections can be classified as loculated or nonloculated. Nonloculated fluid involves more fluid than is simply interposed between tissue planes and has no wall or defined margins. It can be simple or complex in appearance: simple fluid is anechoic, and complex fluid appears more heterogeneous and may contain septations or debris. Subcutaneous edema, which may occur postoperatively or from trauma, venous insufficiency, or inflammatory or infectious processes, appears on ultrasonography as nonloculated fluid interspersed between subcutaneous fat lobules. Loculated fluid collections have well-defined margins or a discrete wall that does not follow normal tissue planes. They can also be simple or complex and can be caused by hematoma, abscess, or ganglion. Less commonly, neoplasms can mimic a loculated fluid collection (Figure 4). A ganglion is a specific type of loculated fluid collection containing synovial fluid arising from a joint or tendon sheath. It tends to occur in specific locations, most commonly around the wrist, most often arising from the dorsal scapholunate ligament and volar wrist between the radial artery and flexor carpi radialis.22 On MRI, it can be difficult to distinguish between small vascular structures and a small ganglion, especially in the hands and feet.23 Ultrasonography can also help identify a Baker cyst, a specific fluid collection arising from the semimembranosus bursa between the medial head of the gastrocnemius tendon and the semimembranosus tendon. Ultrasonography can also detect inflammation, rupture, or leaking associated with a Baker cyst.24 Power Doppler is an ultrasonographic examination that can detect increased blood flow surrounding a fluid collection and determine the likelihood of an acute inflammatory or infectious cause.25 Joint effusion and synovitis Musculoskeletal ultrasonography can help evaluate joints for effusion and synovitis. It is highly sensitive (94%) and specific (95%) for synovitis, making it superior to contrast-enUltrasonography is not appropriate as a survey examination Figure 5. A deep, complex intramuscular soft-tissue mass seen on ultrasonography (A, arrows) required further evaluation with MRI (B, arrow), which better demonstrated the mass’s margins and its relationship to surrounding structures. CONTINUED FROM PAGE 286 Downloaded from www.ccjm.org on August 19, 2022. For personal use only. All other uses require permission. CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 85 • NUMBER 4 APRIL 2018 297 FORNEY AND DELZELL Power Doppler can detect increased blood flow hanced MRI.26,27 The area of concern should be limited to 1 quadrant of a joint (anterior, posterior, medial, or lateral); for problems beyond that, MRI should be considered. A joint effusion appears as a distended joint capsule containing hypoechoic (complex) or anechoic (simple) joint fluid. Complex joint fluid may contain debris and occurs with hemarthrosis, infection, and inflammation.23 Hypertrophied synovium is hypoechoic and can mimic complex joint fluid. Power Doppler evaluation can help distinguish synovitis from joint fluid by demonstrating blood flow, a feature of synovitis but not of simple joint fluid. Power Doppler is the most sensitive means of detecting blood flow, although it does not show direction of flow.28 Using ultrasonography can help to improve disease control and minimize disabling changes by monitoring synovitis therapy. In addition, subclinical
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