According to the Centers for Disease Control, there are 2.6 million visits yearly to the emergency department (ED) for sports-related injuries, the majority of which are musculoskeletal in nature (1). This accounts for 1 in every 4 visits and, in the 5- to 24-year-old age group, equates to 33.9 visits per 1000 persons. Radiologists and physiatrists have utilized ultrasound to diagnose musculoskeletal pathology for >50 years (2). Ultrasound is becoming the most widely used modality in the evaluation of tendon pathology even when other advanced imaging modalities are readily available (3). Ultrasound is also the first mode of imaging available for muscle evaluation and remains the most useful modality to follow muscular trauma over time (4). Ultrasound use has continued to expand, particularly in the pediatric population, in part due to physician and public awareness of the negative effects of radiation exposure from computed tomography (CT) scanning (5).

In the emergency medical care setting, musculoskeletal ultrasound has been used in the evaluation of military personnel during combat, athletes on the sideline, and patients in remote settings with little or no access to standard imaging techniques. In the ED setting, musculoskeletal ultrasound has been shown to reduce the time to diagnosis, assist with difficult diagnoses, improve outcomes, and increase physician ease with musculoskeletal procedures (6, 7, 8, 9, 10).

Ultrasound can be used to diagnose acute traumatic musculoskeletal pathology including fractures, joint effusions, and tears of tendons, ligaments, and muscles. It can also facilitate the diagnosis of acute inflammatory and infectious musculoskeletal pathologic states such as arthritis, tendinitis, tenosynovitis, myositis, and bursitis. Lastly, a number of musculoskeletal procedures can be performed with the aid of ultrasound guidance.

Evaluation of musculoskeletal pathology is typically performed with a high frequency (5 to 17 MHz) linear array transducer. The majority of ultrasound systems used in ED practice provide 5 to 12 MHz transducers for general-purpose imaging (Fig. 21.1A). Less often, a low-frequency (3 to 5 MHz) curvilinear transducer can be used when imaging structures, such as the hip, that are >4 to 5 cm deep (Fig. 21.1B).

Unlike imaging for other applications, the evaluation of musculoskeletal structures does not always include a landmark approach. Instead, the probe should be placed directly over the suspected site of pathology or the patient’s point of maximal tenderness. The area should be examined in a
systematic manner that includes views in the longitudinal and transverse axes. The evaluation of fractures additionally includes visualization of the anterior and posterior cortices (Fig. 21.2). It is common to scan the contralateral unaffected side to obtain images that can be used as a comparison in cases where questionable sonographic findings are encountered.

Musculoskeletal ultrasound presents a few unique challenges to the sonographer. First, most musculoskeletal structures are superficial, and the abnormal contour of the skin surface makes maintaining transducer scanning surface contact difficult. Second, certain musculoskeletal ultrasound evaluations, such as flexor tendon laceration assessment, involve longitudinal visualization during range of motion, which is difficult when the transducer is placed on the flexor surface of the finger. Lastly, the suspected site of pathology is often exquisitely painful, making direct transducer contact uncomfortable. A few measures can be taken to combat these difficulties. First, a modest amount of ultrasound gel should be placed between the transducer and the structure of interest. If this does not yield an adequate image, a water bath immersion or a stand-off pad may be helpful (Fig. 21.3). Water bath immersion becomes an important tool when the area of interest has abnormal contours, a small surface area for probe contact, and is painful to the patient, such as tendon assessment in a finger or toe. Both the transducer and the area requiring examination are placed in a shallow basin filled with water. The water then acts as a medium to conduct ultrasound waves to and from the area of interest without interruption. The technique has been shown to improve image quality without increasing patient discomfort (11).