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Ultrasound-Guided Interscalene Block: Reevaluation of the "Stoplight" Sign and Clinical Implications
Carlo D Franco1, James M Williams
1From the *Department of Anesthesiology, John H. Stroger Jr. Hospital of Cook County; and †Department of Anatomy and Cell Biology, Section of Clinical Anatomy, Rush University Medical Center, Chicago, IL.
Regional Anesthesia and Pain Medicine
|May 21, 2016
Summary
The "stoplight" sign in ultrasound-guided interscalene blocks involves C5, C6 upper, and C6 lower fascicles. Misinterpreting the C6-C7 gap risks intraneural injection at C6.
Area of Science:
- Anatomy
- Ultrasound Imaging
- Regional Anesthesia
Background:
- The
- stoplight
- sign is a common ultrasound finding during interscalene blocks.
- It involves three hypoechoic structures between the scalene muscles.
Purpose of the Study:
- To correlate ultrasound images with brachial plexus anatomy.
- To identify anatomical features influencing interscalene block ultrasound interpretation.
Main Methods:
- Performed 20 brachial plexus dissections on 10 human cadavers.
- Analyzed and measured C5-C7 nerve roots.
- Correlated dissection findings with existing ultrasonographic images.
Main Results:
- C5 root is significantly smaller than C6 and C7.
- C6 and C7 roots often show visible intraroot splitting.
- C5 and C6 roots exhibit variations in their relationship with scalene muscles.
Conclusions:
- The
- stoplight
- sign comprises C5, C6 upper fascicle, and C6 lower fascicle.
- Injection in the perceived C6-C7 gap is an intraneural injection at C6.
- This can lead to potential spread toward the neuraxial space.
