Is the Phoenix Sign Linked to Blood Flow Changes?
A Clinical Trial Overview
Study Title: Evaluating motor function recovery after common fibular nerve block using lidocaine and papaverine.
Published in: BMC Musculoskeletal Disorders, October 23, 2024.
Background
The common fibular nerve is the most frequently trapped nerve in the lower leg. Diagnosing this issue can be challenging, especially if there are other related problems, like lower back pain. A 1% lidocaine injection is often utilized to confirm nerve entrapment and can provide temporary pain relief. Sometimes, a surprising improvement in muscle strength occurs after the injection, known as the “Phoenix sign.” This phenomenon may be due to increased blood circulation around the nerve.
Methods
This study involved a double-blinded, randomized trial with 20 patients. It compared two vasodilators (lidocaine and papaverine) to see which one better produces the Phoenix sign. Using ultrasound, a small amount of either lidocaine or papaverine was injected near the common fibular nerve. Muscle strength in the front of the leg was measured before and four minutes after the injection.
Results
The extensor hallucis longus (EHL) muscle showed significant improvement:
- Lidocaine group: Strength increased from 2.2 to 4.9.
- Papaverine group: Strength increased from 2.1 to 4.4.
Both lidocaine and papaverine led to similar significant improvements in muscle strength.
Conclusion
There was no notable difference in effectiveness between lidocaine and papaverine in enhancing muscle strength. The Phoenix sign likely results from temporary improvements in blood flow to the nerve.
Clinical Trial Registration:
NCT06637046
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