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synovitis and enthesitis (inflammation of insertion sites of tendons or ligaments into bone) detected by ultrasonography may predict future disease and disease flares.29–31 Ultrasonographic guidance for a wide range of procedures is increasing rapidly.32–36 Multiple studies have shown the advantage of ultrasonography-guided aspiration and injection compared with techniques without imaging guidance.37,38 Soft-tissue masses Accurately diagnosing soft-tissue masses can be difficult. A mass may remain indeterminate even after multiple imaging studies, requiring biopsy or surgical referral. However, for a few specific masses, ultrasonography is highly accurate and can eliminate the need for further imaging. Ultrasonography can help evaluate softtissue masses no larger than 5 cm in diameter and no deeper than superficial muscular fascia. If the mass is larger or deeper than that, ultrasonography is less reliable for showing the margins of the mass and its relationship to adjacent structures (Figure 5). Further imaging by MRI may be recommended in such cases. Fortunately, many of the most common soft-tissue masses can be accurately diagnosed with ultrasonography, including lipomas, ganglion cysts, foreign bodies, and simple fluid collections.4,39 Nerve-sheath tumors can also be diagnosed with ultrasonography if the lesion clearly arises from a nerve. Other soft-tissue masses are likely to be indeterminate with ultrasonography, requiring follow-up with MRI with contrast. Tendons Musculoskeletal ultrasonography can be effective for evaluating tendons around joints, especially 1 or a small number of nearby superficial tendons. Tendons particularly well suited for ultrasonographic examination include: • Upper-extremity tendons located in the rotator cuff or around the elbow, and flexor and extensor tendons of the hands; ultrasonographic evaluation of the rotator cuff is highly accurate, equivalent to that of MRI for partial-thickness and full-thickness tearing40–43 • Lower-extremity tendons of the extensor mechanism of the knee, distal hamstring tendons, tendons around the ankle,44–46 and flexor and extensor tendons of the foot. Ultrasonography can also be used to evaluate the tendons about the hip, although resolution is reduced because of the deeper location of these tendons.47 Ultrasonography can help diagnose a variety of tendon abnormalities (Table 1),48,49 including tearing, for which a dynamic examination can be performed. Many tendons have a tendon sheath containing tenosynovium, while others have surrounding peritenon only; either can become thickened and inflamed. Tenosynovitis is a nonspecific finding and may be inflammatory, infectious, or posttraumatic. The presence of tendon sheath fluid alone on ultrasonography can be a normal finding, and some tendon sheaths that communicate with adjacent joints (eg, the long head biceps tendon, the flexor hallucis longus tendon) commonly contain simple fluid.6 A dynamic examination with ultrasonography can help diagnose snapping related to abnormal tendon movement, for example, in the case of intra-sheath and extra-sheath subluxation of the peroneal tendons.45,50,51 Ligaments Ultrasonography can detect abnormalities in many superficial ligaments (Table 1). Ankle. Ankle ligaments are superficial and can be clearly visualized. The diagnostic accuracy of ultrasonography for tearing of the anterior Downloaded from www.ccjm.org on August 19, 2022. For personal use only. All other uses require permission. 298 CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 85 • NUMBER 4 APRIL 2018 MUSCULOSKELETAL ULTRASOUND talofibular ligament may be as high as 100%.50,52,53 Elbow and thumb. The larger of the collateral ligaments of the elbow, especially the ulnar collateral ligament, and the ulnar collateral ligament of the thumb can be effectively evaluated with ultrasonography.54,55 Knee. The collateral ligaments of the knee can be seen with ultrasonography, but injuries of the external ligaments of the knee are often associated with intrinsic derangements that cannot be evaluated with ultrasonography.56,57 Intra-articular ligaments such as the anterior cruciate ligament are also not amenable to ultrasonography. Dynamic examination of a ligament with ultrasonography can help determine the grade of the injury. Deeply located ligaments (eg, around the hip) and ligaments surrounded by bone, such as the Lisfranc ligament, cannot be completely seen on ultrasonography. Muscle Musculoskeletal ultrasonography is useful for small areas of concern within a muscle (Table 1). It can detect muscle strains and tears, intramuscular collections or lesions, and fascial scarring or fascial injuries such as superficial TABLE 1 Ultrasonographic features of musculoskeletal soft tissue Condition Characteristics on ultrasonography Power Doppler Normal tendon Hyperechoic, compact internal fibrillar pattern Anisotropy may be present, mimicking tendinosis or tendon tearing No signal Tendinosis Hypoechoic, focal or diffuse, abnormally thickened, loss of compact fibrillar structure and possibly regions of fiber disruption 48,49 With or without increased power Doppler signal Tearing Can differentiate partial- vs full-thickness tear Complex fluid and blood can mimic intact tendon fibers; if tear is present, fluid
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