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17 Articles in Volume 19, Issue #7
Analgesics of the Future: Inside the Potential of 3 Drug Delivery Systems
Balancing Pain Care - and Opioids - in the Aging Adult
Book Review: A Useful Guide for New Pain Practitioners
Correspondence: Opioid Tapering & Discontinuation
Effective Interventions for Post-Stroke Shoulder Subluxation and Pain
Family: Their Role and Impact on Pain Management
Introducing the "Phoenix Sign:" Improved Vascular Perfusion of the Dorsalis Pedis Artery after a Subanesthetic Dose of Lidocaine
Medication Management of Chronic Pain in Patients with Comorbid Cardiovascular Disease
Multisite Pain May Be Associated with Fractures in the Elderly
Reconciling the New HHS Opioid Tapering Guideline with CDC and State Policies
Research Insights: Impaired Motor Imagery in Chronic Pain Conditions
Tapentadol: A Real-World Look at Misuse, Abuse, and Diversion
Temporomandibular Disorders in Performance Artists (Part 2)
Thoracic Outlet Syndrome Presenting as an Acute Stroke Mimic
Untangling Chronic Pain and Hyperarousal with Heart Rate Variability: A Case Report
What topicals exist for post-herpetic neuralgia pain?
When to Keep Your License: Older Physicians and Boundary Issues

Introducing the "Phoenix Sign:" Improved Vascular Perfusion of the Dorsalis Pedis Artery after a Subanesthetic Dose of Lidocaine

A case study illustrates efficacy of the nerve block and decompression in a patient with post-traumatic chronic left lower extremity pain.
Pages 51-54

Paradoxically, improved motor function was observed clinically by the authors several years ago after administering a small subanesthetic dose of lidocaine under sonographic guidance to reduce the pain associated with a common fibular nerve entrapment in a patient with almost no ability to dorsiflex their foot. The use of peripheral nerve blocks has been well established in the determination and identification of those nerves that are thought to be first-order pain generators so that accurate diagnosis and appropriate intervention can be planned.1 However, there has been no previous report in the literature of a local anesthetic nerve block improving peripheral nerve function to our knowledge.

Since discovery of this phenomenon in 2017, we have repeated this test in hundreds of administrations. The findings have been consistent and proven extremely reliable in both the confirmation of a nerve compression and ultimate patient outcome after nerve decompression surgery, when clinically there was no provocation sign, or Tinel’s sign, present. The lead author (Barrett) coined this phenomenon, the “Phoenix Sign,” as the once non-functioning common fibular nerve “rose from the ashes,” and with a drop foot, the patient was suddenly able to dorsiflex their foot.

Before making clinical observation, there were initially a small subset of patients afflicted with a drop foot due to a common fibular nerve palsy or entrapment that were not offered the chance for nerve decompression surgery because they would have not met the selection criteria for surgical intervention. Our team now uses this test, which we are calling the “Phoenix sign block,” routinely on patients who manifest a motor weakness in the extensors of their lower extremity below the knee, as this sign has also proved valuable in the predictive outcome of surgical nerve decompression of the common fibular nerve. If there is an improvement in motor strength noted, it is referred to as a positive Phoenix Sign; if there is no response, it is noted as a negative Phoenix Sign.

Subsequently, after hundreds of these infiltrations, our team made further observations of not only improved motor function but also improvements in vascularity and cutaneous sensation distally to the block.

Hypothesized Mechanism of Action
for the “Phoenix Sign”

Local anesthetics, aside from cocaine, provide vasodilatory effects.2 The authors hypothesize that because of this vascular effect, there is a temporary increase in the focal vascular supply at the site of nerve entrapment. In peripheral nerve decompression surgery, an almost immediate filling of the vaso nervorum is frequently observed after the nerve is decompressed. The ischemia of the nerve is reduced and improved function is not only demonstrated clinically in the post-anesthesia care unit (PACU) but also with intraoperative EMG monitoring.3,4 See Figure 1.

Figure 1. In 6 minutes after peripheral nerve decompression of the nerve seen on left, there is evidence of vaso nervorum seen in the photo on right.

To further support this hypothesis, the authors tested several patients who demonstrated improvements in motor strength with plain lidocaine. When these same patients were infiltrated with lidocaine with 1:100,000 epinephrine (vasoconstrictor), they did not show a positive “Phoenix Sign.” The following retrospective case report illustrates these findings and the utility of the diagnostic peripheral nerve block and subsequent peripheral nerve decompression. (More on lidocaine as a delivery system.)

Case History

A 63-year-old male with post-traumatic chronic left lower extremity pain presented to our clinic in 2017. His history of present illness started with a left ankle injury and tibial fracture resulting from playing baseball 28 years prior. He underwent eight surgical procedures, implantation of a spinal cord stimulator, multiple lumbar epidural steroid injections (LESIs), and has taken high levels of opioids since his injury. He reported a history of constant burning pain at all times with a pain level never less than 7 out of 10, which greatly interfered with his general activity, ability to work, enjoy life, and sleep. His pain has further caused an extremely antalgic gait with subsequent closed kinetic chain compensations, increasing his lower back pain. He is a non-insulin-dependent diabetic (NIDDM) with hepatitis and cardiovascular disease.

The patient returned to our clinic in April 2019 with an unchanged HPI, except that he now had his diabetes under better control. (Note: There was a gap in care due to the patient temporarily losing insurance benefits). Physical examination revealed that he had no palpable dorsalis pedis pulse, with minimal evidence of dorsalis pedis perfusion with high-resolution Doppler ultrasonography. The waveform had a 0-1.0 cm amplitude, with a slight crescent shape (see Figure 2).

Figure 2. This Doppler study shows a small presence of a dorsalis pedis pulse but the frequency is slow and the amplitude is minimal.

At this time, infiltration of 0.4 ccs of 1% lidocaine plain was administered under guided ultrasound adjacent to the common fibular nerve. After less than 4 minutes, the amplitude of the waveform increased significantly – to about 2.5 cm, and the artery, though still slightly crescent-shaped, was much stronger in addition to being palpable (see Figure 3).


Figure 3. In less than 4 minutes, there was a significant increase in the amplitude and frequency of the dorsalis pedis waveforms.

Radiographic evaluation revealed fusions of the 1st metatarsal phalangeal joint, midfoot fusions, a derangement of the central 3 metatarsal phalangeal joints, severe 1st metatarsal elevatus, and remaining staples. See Figures 4a-c.


Figure 4a. In photos 4a, 4b, and 4c, severe osseous derangement can be seen with dramatic osteopenia due to the patient’s inability to walk.

After completion of a comprehensive lower extremity peripheral nerve exam, a biomechanical exam, a peripheral nerve block as described above, and a radiographic evaluation, the following assessments were determined:

  • common fibular nerve entrapment, left
  • superficial fibular nerve entrapment at the foraminal level, left
  • proximal tibial nerve entrapment at soleal sling level, left
  • tibial nerve entrapment at the medial ankle, left
  • medial plantar nerve entrapment, left
  • lateral plantar nerve entrapment, left
  • sinus tarsi syndrome, left
  • painful internal hardware, left
  • metatarsalgia
  • sural neuritis, left
  • chronic pain in the left lower extremity
  • painful hypertrophic scar with scar neuroma, left
  • exertional compartment syndrome, anterior and lateral compartments, left

Treatment Plan

The patient was casted for a custom left ankle foot orthosis (AFO) brace with a tarsal tunnel cutout to improve his symptoms of tarsal tunnel syndrome and to provide left ankle stabilization. Because of his poor vasculature but improvement in vascular perfusion after the Phoenix Sign block and complaints of pain in the lower leg, it was recommended he undergo the following surgical procedures:

  • left common fibular nerve tri-septal decompression (common, distal, and superficial fibular nerves at the level of the fibular neck)
  • left superficial fibular nerve decompression at the foraminal level with anterior and lateral fasciotomies
  • removal of painful hardware/screw in the left ankle.

Based on the vascularity being diminished in his foot and the fact that improved vascular perfusion could be expected after proximal nerve decompressions, staged surgeries were planned, predicated on the result of the first intervention.

On May 13, 2019, all three recommended procedures were performed. The common fibular and superficial fibular nerve decompressions not only increased his blood flow by at least 200% as assessed by the amplitude of the post-operative Doppler waveforms, but also reduced and/or alleviated his symptoms of pain. Additionally, he reported at his first post-operative follow-up (1 week) that his foot was no longer cold; he continues to report this improvement to date. The patient took pain medications as part of post-operative recovery but did not take vasodilators.


At the 8-week follow-up appointment on July 16, 2019, the artery appeared to be more of an oval shape with a strong and steady pulse near the deep fibular nerve. In the ultrasound of the left dorsalis pedis, the waveform was consistently at approximately a 2.0 cm amplitude (see Figures 5 and 6). The patient was seen again on August 11 (about a 12-week follow-up) and still manifested the same improvement in vascularity; he is now scheduled for further forefoot reconstructive surgery. At the time of this writing, the pain in the patient’s lower leg was completely gone and his sensation continues to improve. Positive trophic changes were also noted in his foot and leg (see Figure 7).

Figure 5. This waveform is inverted, but has maintained a good frequency and amplitude 8 weeks post-surgery, supporting improvement in the autonomic peripheral nerve subsequent to nerve decompression


Figure 6. On the left is the waveform prior to a “Phoenix Sign” block compared to the right which is post-surgery at 8 weeks.


Figure 7. This images shows an improvement in skin color and temperature. The two proximal incisions were used to decompress the common peroneal nerve and superficial peroneal nerve. The other incisions were from previous reconstructions.


By addressing common fibular nerve compressions with surgical neurolysis, the authors have routinely found that the case patient exhibits improved motor strength and sensation within that nerve distribution. In addition, there has been consistent improvement in vascularity distal to the nerve decompressions outside the parameters of this nerve distribution, which the authors acknowledge is paradoxical. Skin changes associated with autonomic dysfunction have improved in many patients following peripheral nerve decompression, which has been documented by preoperative and post-operative epidermal nerve density biopsies where there have been increases of nerve fiber count—in some cases back to or above the normal level. The improvement of vascular perfusion has been reported by Trignano, et al, with decompression of the tarsal tunnel in diabetic patients.5 It has been well established that peripheral nerve decompressions in diabetic patients with superimposed nerve compressions can improve sensation, decrease pain, and prevent ulceration and ultimately amputation in some cases.4,6

The fact that improved peripheral nerve function following decompression of focal entrapments leads to improved vascular function has many obvious potential benefits for the patient concerning conditions related to blood flow. Currently, the treatments for peripheral arterial disease (PAD) include: management of the symptoms, encouragement of a healthier lifestyle, implementation of various medications, and/or procedures such as angioplasty, bypass, and thrombolytic therapy.7-10

However, since improved nerve function may lead to improved vascular function, further study is needed to see if there may be a valid role for peripheral nerve decompression before endovascular intervention. This approach would aim to facilitate distal endovascular access. In addition, it may facilitate more distal reconstructive surgery of biomechanical pathology that would be precluded due to impaired vascular perfusion prior to the improvement seen from proximal nerve decompression surgery. This outcome is demonstrated in the presented case study.


The “Phoenix Sign” is a highly reproducible and reliable peripheral nerve block technique for determination and confirmation of lower extremity peripheral nerve focal entrapment—especially in cases where there are not the usual clinical signs of entrapment such as a positive Tinel’s sign or provocation sign. This peripheral nerve block also gives insight into what level of motor improvement could be expected after surgical nerve decompression. 


For citation purposes, this article's print title appeared as follows: Improved Vascular Perfusion of the Dorsalis Pedis Artery after Sonographic Guided Infiltration of a Subanesthetic Dose of Lidocaine—the “Phoenix Sign.” A retrospective case study illustrates efficacy of the nerve block and subsequent common fibular nerve decompression in a patient with post-traumatic chronic left lower extremity pain.

Last updated on: December 9, 2019
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