Last updated: October 10, 2014
Synonyms: Ultrasound, US
CPT Codes: Extremity US 76881; Limited US extremity 76882; US arthrocentesis/injection 20600 (small); 20605 (medium); 20610 (large joint); US guidance of needle placement 76942
Description: Ultrasonography uses analysis of reflections of sound waves to define tissue anatomy. There has been increasing interest in the musculoskeletal applications of US.
Method: Conventional gray scale (B-mode) US can clearly define articular and periarticular structures. Different than traditional radiography, it can assess non-calcified articular and periarticular structures, such as tendons, lligaments, cartilage and synovium. US is more sensitive than plain X-rays in detecting disruption in the bony cortex (i.e., erosions). Synovial hypertrophy, as seen in inflammatory arthritides, can be detected and quantified. Typically, transducers in the range of 7.5 to 15 MHz frequency have been used for US of musculoskeletal structures. Higher frequencies provide greater resolution and finer tissue detail, but tissue penetration decreases with increasing frequency. The optimal settings depend on the structures to be assessed. Power Doppler techniques have also proven very useful in musculoskeletal US. Doppler US assesses the mean frequency shift of sound waves echoing from moving objects and is used for defining large-vessel, high-velocity blood flow (e.g. large arteries). Power Doppler US encodes the amplitude of the Doppler signal and is useful for assessing blood flow in smaller vessels, such as those in the inflamed synovium. Power Doppler US findings, typically graded on a semiquantitive scale (0-3+) correlate with clinical findings and identify joints that will subsequently develop structural damage.
Indications: Many joints are amenable to US examination. Joint fluid, synovium, and periarticular structures are readily visualized. US is very useful in the delineation of abnormalities in the periarticular structures of the shoulder, such as the rotator cuff apparatus, and is therefore very useful in the evaluation of a painful shoulder. US of the knee allows identification of popliteal (Baker’s) cysts versus deep vein thrombosis in patients with acute, painful swelling of the calf. For many joints, US can facilitate the accurate placement of needles and hence injected medications within the joint space. In the small joints of the hands and feet, US has a sensitivity that is comparable with MRI in detecting periarticular erosions; both of these modalities are superior to conventional radiography in that regard. Power doppler imaging has been shown to correlate with measures of inflammation and thus may be a useful tool for the longitudinal assessment of disease activity within joints in conditions such as RA.
Advantages/Limitations: High sensitivity to relevant pathology, relatively low cost, lack of exposure to ionizing radiation, lack of adverse effects, ease of performance, and ready access make US attractive. Limitations of US include the dependence of imaging techniques on the skill of the examiner.
Cost: Typical charges for musculoskeletal US examination are $150–300.
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