TITLE:
Predictive Reliability of the Phoenix Sign for the Outcome of Common Fibular (Peroneal) Nerve Decompression Surgery
AUTHORS:
Stephen L. Barrett, Adam Khan, Victoria Brown, Erik Rosas, Sequioa Du Casse, Porscha Bailey
KEYWORDS:
Peripheral Nerve Block, Drop Foot, Ultrasound Guidance, Common Peroneal Nerve Entrapment, Common Fibular Nerve Entrapment
JOURNAL NAME:
Open Journal of Orthopedics,
Vol.10 No.9,
September
23,
2020
ABSTRACT: A positive Phoenix sign occurs when a patient, with a suspected focal
nerve entrapment of the Common Fibular (Peroneal) Nerve (CFN) at the level of
the fibular neck, demonstrates an improvement in dorsifexion after an
ultrasound guided infiltration of a sub-anesthetic dose of lidocaine. Less than 5 cc’s
of 1% or 2% lidocaine is utilized and the effect is seen within minutes after
the infiltration, but usually lasts only 10 minutes. This effect may be due to
the vasodilatory action of lidocaine on the microcirculation in the area of
infiltration. This nerve block has significant diagnostic utility as it is
highly specific in the confirmation of true focal entrapment of the CFN, has
high predictive value for a patient who may undergo surgical nerve
decompression if they have demonstrated a positive Phoenix Sign, and may help
in the surgical decision-making process in patients who have had a drop foot
for many years but still may regain some motor function after decompression. In
this retrospective review, 26 patients were tested, and 25 of this
cohort demonstrated a Positive Phoenix Sign
(an increase in dorsiflexion strength of the Extensor Hallucis Longus
muscle (EHL)). One patient had no response to the peripheral nerve block. Of the 25 patients who demonstrated a positive “Phoenix Sign” and underwent nerve decompression of the CFN, and 25 (100%)
showed an increase in dorsiflexion strength of the EHL after nerve decompression surgery of the CFN. The one patient in
this cohort who did not demonstrate
any improvement in dorsiflexion of the EHL after the nerve block did not
have any improvement after surgery.