The present protocol describes a technique for the standardization of median nerve ultrasound in cases of suspected carpal tunnel syndrome.
The use of neuromuscular ultrasound greatly enhances the evaluation of carpal tunnel syndrome as an adjunct diagnostic tool as it provides dynamic and structural information about the median nerve and its surrounding anatomy. Neuromuscular ultrasound aids in diagnostic accuracy (when used with electrodiagnostic testing) and offers etiologic information as a non-invasive, painless, cost-effective, and radiation-free imaging technology that can be easily carried out at the bedside for immediate interpretation. Neuromuscular ultrasound has the limitation of subjectivity, and the need for training and experience will affect the interpretation of results. This article describes a basic practical guide to visualizing the median nerve using neuromuscular ultrasound in a step-by-step manner to aid in the evaluation of carpal tunnel syndrome. Even though the use of ultrasound in the assessment of median nerve entrapment has been long established, there has been no recognized standard protocol. The present protocol aims to provide clear and concise instructions to describe a standard technique to visualize the median nerve through diagnostic ultrasound.
Neuromuscular ultrasound (NMUS) is an increasingly popular method that may be used in conjunction with electrodiagnostic and clinical information in order to diagnose, prognosticate, and guide injection procedures in patients with neuromuscular conditions1. Anatomical structures such as nerves, muscles, bones, and tendons can be identified with high-resolution ultrasound that can refine a diagnosis and provide structural etiology when present. Visualizing the median nerve in the carpal tunnel space-the site of the most common entrapment neuropathy-is one of the most mainstream uses of neuromuscular ultrasound. The rationale for this technique is based on evidence that NMUS is an accurate procedure that may help localize median nerve pathology and guide procedural interventions1,2,3,4. A recent expert consensus found that using both neuromuscular ultrasound and electrodiagnostic study for median nerve pathology is the superior method as opposed to either method alone5. The consensus also describes patient scenarios where the addition of median nerve ultrasound is advantageous for non-localizing or normal electrodiagnostic in the setting of clinical carpal tunnel symptoms, atypical electrodiagnostic, failed CTS surgery, and carpal tunnel syndrome due to a structural abnormality5.
General advantages to the use of NMUS include that it is a non-invasive bedside test that is low cost compared to other diagnostic options, well-tolerated, and can provide important morphologic information that is not uncovered when using other modalities. NMUS evaluation has been shown to be a useful tool in redirecting management strategies in patients6,7,8,9,10,11,12,13.
While there is currently no standard technique for visualization of the median nerve in the carpal tunnel space with ultrasound, there are widely accepted recommendations on how to approach imaging. Through the described procedure, the goal is to establish a clinical reference that clinicians may use to obtainconsistent, high-quality images and measurements. Limitations to this technique include having the proper equipment, including a high-frequency (15 to 22 MHz) linear array transducer used to evaluate the median nerve in two distinct planes. Another limitation to this technique will be proper clinical experience, as it is important to understand the anatomical positioning of the transducer prior to evaluating the nerve, so that correct interpretation of the landmarks is achieved. The present protocol describes the steps of clinical imaging of the median nerve and evaluation of median nerve entrapment.
As ultrasound visualization is a subjective process and operator dependent, it is critical to follow an organized approach in order to accurately determine parameters, including cross-sectional area, mobility, echogenicity, and vascularity. The most important steps include holding the probe perpendicular to the nerve while the patient is in the correct position. In addition, visualizing the nerve throughout its course proximally and distally to the area of entrapment allows for discovering further pathology or othe…
The authors have nothing to disclose.
We would like to thank the staff of the Wake Forest Baptist Health Neuromuscular department for their support and assistance.
GE CARES LOGIQ insite exc ultrasound Machine | any | 6066032WX0 | |
High-frequency (12 to 18 MHz) linear array transducer | GE | ||
Ultrasound Gel | Aquasonic |
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