Ultrasound (US) is a wonderful imaging modality for the assessment of the musculoskeletal system. It is a noninvasive, nonirradiating, cost-effective, and widely available technique. It allows real-time dynamic assessment of muscles, tendons, and nerves and can even generate images with greater spatial resolution than those obtained with standard clinical MRI techniques, for example for the small and/or distal structures.
The aim of this text is to present the usefulness of ultrasound regarding the main normal and pathological aspects of musculoskeletal structures.
The development of compact real-time ultrasound systems in the 1980s and the subsequent availability of broadband high-frequency linear-array transducers in the 1990s have dramatically improved the accuracy of clinical assessment of musculoskeletal disorders.1 Ultrasound exploration appears as an essential complement to many radiographic assessments of the musculoskeletal system.
The choice of transducer frequency depends on the overall size of the structure, its position relative to the skin (deep or superficial), and the conspicuity of the intervening soft tissue planes. Superficial structures require small-sized probes with high frequencies (7.5–24 MHz), while deep structures require low-frequency probes (3.5–5 MHz).1
The brightness of the images (echogenicity) depends on the degree of reflection of the ultrasound waves. The echogenicity of a tissue depends on its inner characteristics and on the transducer frequency. The terms used to describe such characteristics include hyperechoic (white signal), isoechoic, hypoechoic, and anechoic (black) echogenicity. In general, bones and gas-like structures are most echogenic, and fluids such as joint effusion are less echogenic.1
Assessing musculoskeletal disorders via ultrasound has many advantages as compared to other imaging modalities1–5:
It is well tolerated and has no contraindication, unlike MR imaging.
It is a nonionizing exploration, in opposition with CT or conventional X-ray examinations.
It can effectively image patients with orthopaedic hardware that causes significant artefacts in MR imaging.
It is noninvasive and does not require intravenous contrast administration in the clinical practice, as it can provide information about blood flow and the degree of tissue vascularity thanks to the use of color Doppler and power Doppler.1–3,6
It is cost-effective and widely available. An ultrasound examination of an extremity costs about three times less than an MRI examination.7
It allows real-time dynamic assessment of muscles, tendons, and nerves. Using passive and active movements, or isolated muscle contractions, is fundamental for the depiction of tendon and bursal impingements (such as subacromial impingement), nerve impingements, tendon and nerve instability, and muscle herniation, as well as to improve the depiction of small lesion such as tears.8,9
It facilitates bilateral comparison. A wide degree of anatomic variability exists in the musculoskeletal system. Consequently, the contralateral comparison is generally very useful when deciding whether an abnormality is present ...