Is the Phoenix Sign Phenomenon Due to Vasodilation? A Double-Blinded, Randomized Controlled Trial Comparing Motor Function Recovery After Diagnostic Common Fibular Nerve Block with Lidocaine and Papaverine

Is the Phoenix Sign Phenomenon Due to Vasodilation? A Double-Blinded, Randomized Controlled Trial Comparing Motor Function Recovery After Diagnostic Common Fibular Nerve Block with Lidocaine and Papaverine | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Is the Phoenix Sign Phenomenon Due to Vasodilation? A Double-Blinded, Randomized Controlled Trial Comparing Motor Function Recovery After Diagnostic Common Fibular Nerve Block with Lidocaine and Papaverine Stephen L. Barrett, Bailey Boyd, Sequioa DuCasse, Wajdi Nassier, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4802432/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Oct, 2024 Read the published version in BMC Musculoskeletal Disorders → Version 1 posted 10 You are reading this latest preprint version Abstract Background Focal entrapment of the common fibular (peroneal) nerve (CFN) is the most common nerve entrapment in the lower extremity. Accurate diagnosis can be difficult due to co-existent pathology such as low back pathology. A 1% lidocaine block of CFN is often used to confirm the local entrapment pathology and demonstrate possibility of pain relief. A surprising, unexpected and temporary strengthening of CFN supplied ankle and foot muscles is occasionally produced, termed the Phoenix sign. Aetiology of this phenomenon has been puzzling, but restoration of neural circulation and nutrition via improved local blood flow has been postulated to be responsible. Methods This is a double-blinded, randomized, prospective controlled trial of 19 patients, comparing 2 vasodilating agents and their ability to produce the Phoenix effect. Ultrasound guided infiltration of 0.3 mL 1% lidocaine or papaverine HCl 10 mg/mL was executed adjacent to CFN. Motor strength pre- infiltration and 4 minutes post-infiltration were measured for anterior compartment muscles utilizing MRC manual motor testing reported on a 0–5 scale. The extensor hallucis longus (EHL) muscle proved to be the most significant. Results Average motor strength of the EHL improved from 2.2 (+/-0.40) to 4.9 (+/-0.32).) in the lidocaine group. In the papaverine group, pre-infiltration EHL motor strength averaging 2.1 (+/-0.93) improved to 4.4 (+/- 1.01) post-infiltration. Papaverine and lidocaine produced similar statistically significant increases in muscle strength (p = < 0.05). Conclusion There was no difference between small local infiltrations of lidocaine or papaverine in production of increased anterior compartment EHL motor strength. It is most likely that the Phoenix Effect is explained by temporary local improvements in the microcirculation of the CFN vasa nervorum. Drop Foot vascular perfusion peripheral nerve block common peroneal nerve peripheral nerve Figures Figure 1 Figure 2 Figure 3 Figure 4 1 Background Entrapment of the common fibular nerve (CFN) at the level of the fibular neck in the lower extremity is the most commonly recognized peripheral nerve entrapment in the lower extremity [ 1 – 3 ]. It can cause chronic lower extremity pain, abnormal sensation, or motor weakness. Due to variations of clinical presentation, and comorbidities such as low back pain, recognition and diagnosis of this pathology can be complicated. Early diagnosis and treatment can prevent or mitigate musculoskeletal and neurological sequelae that can occur with delay in treatment [ 4 ]. One of the consequences of CFN entrapment is Drop Foot, due to a paralysis of the muscles of the anterior and lateral compartment of the leg. However, Drop Foot can have other causes, such as traumatic injury, rapid weight loss in bariatric surgery, positioning during or after knee and hip surgery, herniation of a lumbar disc, intraneural ganglia, long periods of squatting, and metabolic conditions causing neural oedema and enlargement such as type II diabetes [ 4 , 5 ]. Local lidocaine injection is used clinically to test whether pain relief may be expected after neurolysis. Recent literature reports that patients with Drop Foot can gain motor strength after an injection of a minimal volume of 1% lidocaine adjacent to the CFN [ 6 ]. After the injection, an effect was seen where the patient would temporarily regain partial or full dorsiflexion. This is named the Phoenix Sign. A positive Phoenix sign is helpful in the diagnosis and assessment of CFN palsy, allowing the clinician to reliably identify a focal peripheral nerve compression. Anaesthetic infiltration is placed adjacent to the CFN under sonographic guidance in patients with complete drop foot or significantly weakened motor strength of the muscles of the anterior compartment of the leg (Extensor Hallucis Longus (EHL), Tibialis Anterior (TA), and Extensor Digitorum Longus (EDL). This brief, lidocaine-induced improvement of anterior compartment muscle strength can allow the clinician to reliably differentiate a focal peripheral nerve compression from a CNS or more central peripheral nerve aetiology. There has been much conjecture about the explanation of this observation. Might this phenomenon be due to some type of neural reflex from the local anaesthetic agent, or could it be simply due to the vasodilatory effect of lidocaine? This study was designed to examine whether the Phoenix Effect produced by lidocaine and the known vasodilator papaverine were comparable. 2 Methods A double-blinded, randomised, prospective controlled trial was conducted at US Neuropathy Centers in Marietta, GA, under the approval of the Kennesaw State University Institutional Review Board. Patients with weak dorsiflexion of the ankle or a drop foot were recruited from the existing clinical practice at US Neuropathy Centers. Cohort inclusion criteria also included a stable medical and medication status, ages 18–85, speaking English as the primary language, and ambulatory. Walking aids or ankle-foot orthosis were permitted. Baseline characteristics of the 2 groups are shown in Table 1 (Show gender, cohort age ranges, pertinent medical diagnosis or history). Based on the inclusion criteria, only 20 patients were enrolled (Fig. 1 ). Patients were recruited over a period of 1 year and two months from January 2021 to March 2022 with no requirement for follow-up. The enrollment was concluded due to this being a pilot study. Table 1 Patient demographics with gender, cohort age ranges, and pertinent medical history Subject Gender Age PMHx 1 F 52 Diabetes 2 F 39 Fibromyalgia Cervical spinal fusion Polyneuropathy 3 F 50 Tarsal Tunnel Obese 5 M 68 CMT 6 M 53 Sleep apnoea 7 F 54 Diabetes Incomplete Paraplegia 8 M 56 Diabetes Chronic Pain 9 F 62 Chronic pain 10 F 65 Small Fiber Neuropathy Restless leg syndrome Diabetes PVD 11 F 35 Diabetes 12 M 71 Lumbar Pain 13 F 60 Neuropathy 14 F 28 Chronic pain (hx of MVA) 15 F 66 Peripheral Neuropathy 16 F 59 Plantar fasciitis 17 F 57 Lumbar Radiculopathy 18 F 57 Lumbar Radiculopathy 19 F 64 Diabetes PAD Peripheral Neuropathy 20 M 62 Peripheral Neuropathy Participants were randomised by the throw of dice to injection of 0.3 cc of Papaverine HCl 10 mg/mL or 0.3 cc of 1% Lidocaine HCl adjacent to CFN in a room separate from patient room. Injection solutions were prepared by non-blinded assistants and were visually indistinguishable. Patients and physicians are blinded to drugs received. Motor strength of the Extensor Hallucis Longus (EHL), Tibialis Anterior (TA), and Extensor Digitorum Longus (EDL) muscles were tested. Strength was rated according to the Medical Research Council Manual Muscle Testing scale 0–5. The CFN at the fibular neck was identified under high-resolution ultrasound imaging. The injection site was prepared with alcohol, and ethyl chloride was used to anaesthetise the skin. A 30-gauge 1-inch needle was inserted adjacent to, but not within, the CFN and 0.3cc of drug delivered (Fig. 4 ). The investigator then waited approximately five minutes and re-tested motor strength of the Extensor Hallucis Longus (EHL), Tibialis Anterior (TA), and Extensor Digitorum Longus (EDL) muscles manually. 3 Results The baseline and post-injection muscle strength of TA, EHL and EDL was rated as 0 to 5 according to the Medical Research Council Manual Muscle Testing scale as in Ciesla, et al. [ 7 ]. Post-injection strength was tested after 4–6 minutes. EHL, TA, and EDL strength before and after papaverine or lidocaine injections is reported for all subjects. EHL showed the most consistent and severe baseline weakness but improved in every subject and regained full power in 9/11 of lidocaine subjects and 6/9 of papaverine subjects (Figs. 2 and 3). Baseline TA strength was normal in greater than half the cases. EDL baseline strength was lower, but all achieved full strength after injection but one case. One subject had a history of Charcot Marie Tooth (CMT) disease. CMT subject was an outlier, showing no improvements in any muscle but EHL and even then, just 1 level from muscle recovery 1 to 2 strength after papaverine injection (see Table 2 ). Table 2 Changes in MMT strength of CFN supplied foot and ankle muscles after injection of lidocaine or papaverine vasodilator drug Muscle Drug MMT Mean Strength Regained any strength Regained 5/5 strength P value Pre Post Change EHL Lidocaine 2.2 4.9 2.7 11 / 11 9 / 11 < 0.001 Papaverine 2.1 4.4 2.3 9 / 9 6 / 9 < 0.001 TA Lidocaine 4.5 5.0 0.5 3 / 3 3 / 11 < 0.001 Papaverine 4.1 4.6 0.5 4 / 5 4 / 9 < 0.05 EDL Lidocaine 3.4 5 1.6 11 / 11 11 / 11 0.05 Papaverine 3.3 4.6 1.3 7 / 8 7 / 9 < 0.002 4 Discussion Accurate diagnosis of lower extremity peripheral nerve entrapments can be difficult even for the most experienced clinicians. When there may be coexisting pathology such as previous CNS disturbances like stroke and multiple sclerosis or low back pathology, a simple diagnosis becomes more complicated. Interestingly, we have seen patients who have a documented history of a CNS pathology that demonstrated a positive Phoenix Sign. Universally, this small cohort of patients who subsequently underwent nerve decompression surgery enjoyed improved muscle strength, indicating the patient had to have had a “double-crush”, two-pathology presentation [ 8 ] with at least some substantive nerve compression of the CFN at the neck of the fibula. Otherwise, post-operative improvements would not have been seen. These observations reinforce the potential value of this diagnostic nerve block in patients suffering from CFN palsy who also have documented CNS pathology. The accurate diagnosis will be missed or delayed in many cases if the Phoenix sign is not sought, leaving patients with a condition that could have been treated successfully with peripheral nerve decompression surgery. This would make recovery of better or normal musculoskeletal function in a high percentage of cases less likely [ 9 ]. Our findings presented in this paper strongly support the vasodilation hypothesis as explaining the Phoenix Sign. Both plain lidocaine and papaverine produced temporary restoration of motor function. While there is a paucity of literature regarding the efficacy of diagnostic peripheral nerve block to predict surgical outcomes, Dr. Nirenberg published an important paper in 2020 demonstrating similar diagnostic findings where he injected 4 cc of 1% plain lidocaine into the fibularis (peroneus) longus muscle belly adjacent to where the common fibular nerve courses around the neck of the fibula [ 10 ]. His hypothesis “...that the peroneus longus muscle becomes flaccid or relaxed, to an extent, allowing compression of the muscle (and its underlying fascia band) on the CFN to lessen, reducing and/or eliminating the nerve entrapment.” Our findings did not support his hypothesis of muscle relaxation as the mechanism behind his clinical observations because our administration of lidocaine was always below 0.5 cc (a miniscule amount that empirically could not be believed to cause significant muscular relaxation even if administered into the muscle) and was not infiltrated intramuscularly. Additionally, the musculature had increased motor strength 4 minutes after infiltration, which would not be expected from a muscle that is rendered flaccid. While papaverine is known to have some small indirect effects on smooth muscle, our administration of it was not intramuscular, and the same increase in motor strength was observed after its administration, as was seen with the patients that received lidocaine. Regardless of the hypothesis proffered by Nirenberg’s work, it does demonstrate the ability to assist in the verification of a focal nerve entrapment of the common fibular nerve and gives prognostic insight correlative to what we have observed with the Phoenix Sign. In their rat model of chronic nerve compression, MacKinnon and Dellon [11] showed that at approximately 6 months post compression of the sciatic nerve, a very significant level of nerve degeneration can be seen histologically, and that after decompression, even in the presence of diabetes, the peripheral nerve can regenerate. Secondary nerve regeneration has been understood and well documented by Zhong et al. [ 12 ] and Juckett et al. [ 13 ]. Uemura and colleagues [ 14 ] in 2021 have demonstrated increased vascular circulation around the tibial nerve in diabetic neuropathic patients after tarsal tunnel decompression surgery. Specifically, they showed a thirty percent increase in vascularity around the tibial nerve illustrating how improvement in nerve function is related to improvement in vascularity. Anderson et al reinforce this fact in their study which demonstrated functional improvement of muscles in the leg via intraoperative EMG following CFN decompression in patients with diabetic neuropathy. Almost 43% of both fibularis longus and TA muscles regained strength from baseline in one leg. The return of microcirculation via the decompression of vasa nervorum along with CFN was attributed to the rapid functional improvement in muscles although the authors’ study was not designed for this type of investigation [ 15 ]. Drop Foot is a commonly seen complication following knee and hip replacement surgery. Kremers et al. [ 16 ] reported that by 2010 there had been 4.7 million total knee arthroplasties and 2.5 million hip replacements performed. Estimates of CFN complications following hip arthroplasty are 0.44% and post- knee arthroplasty range from 0.3–1.3% [ 5 , 17 ]. It is possible that these percentages are underestimated, as Beswick et al. showed a much higher incidence of chronic post-surgical pain of 10–34% following knee arthroplasty and 7–23% following hip arthroplasty procedures [ 18 ]. It is generally believed that peripheral nerve injury, especially to the CFN, makes up the lion’s share of these postoperative complications [ 18 ]. With extrapolation of the lower estimates, the incidence of drop foot or post arthroplasty pain due to CFN injury could comprise a significant percentage of the 124,100 to 721,000 cases annually. 5 Limitations of the study The purpose of this study was simply to determine whether a small local injection of the vasodilator papaverine exhibited an objective temporary increase in motor strength as does 1% lidocaine. Our results show it does, confirming that local circulation restoration can be a part of focal CFN dysfunction. This study had a small cohort size, but the result is significant by statistical analysis. Further investigation confirming the result with a larger number of subjects would be ideal. The study cohort is quite heterogeneous in diagnoses, yet the Phoenix sign correctly predicted motor improvement in all but the Charcot-Marie-Tooth subject. The double blinded, randomized, prospective design of this study is a strength despite the small sample size. A larger number of subjects would be ideal. Additionally, there is always a question of subject heterogeneity/homogeneity within the subject group. The purpose of this study was simply to determine if the papaverine group exhibited an increase in motor strength similar to that as seen within the lidocaine group when these medications were delivered at the site of a focal nerve compression. Focal nerve compression can be independent of any antecedent or concurrent medical comorbidities and the fact that there was some medical diversity within the subject group showed the universality of effect of the diagnostic blocks. 6 Conclusion Based on the results seen, there is no statistical difference in the increase of motor strength for the dorsiflexors after either infiltration with lidocaine or papaverine. These findings, although it is a small cohort, strongly suggest that the phenomenon known as the Phoenix Sign is due to the vasodilation component of the infiltrated local anaesthetic, and not some other unknown neurological explanation. With proper dosage and technique of ultrasound guided infiltration, the findings from this diagnostic block can provide the clinician with improved diagnostic accuracy of CFN entrapment. Additionally, the patient who demonstrates a positive Phoenix sign has a very high likelihood of successful peripheral nerve surgical decompression. Abbreviations CFN Common Fibular Nerve EHL Extensor Hallucis Longus TA Tibialis Anterior EDL Extensor Digitorum Longus MMT Manual Muscle Testing CNS Central Nervous System Declarations Acknowledgements Heather Stein, Ph.D. helped with preparing the manuscript and supporting documents for final submission. Author contributions SLB is the primary author and major contributor in writing the manuscript as well as interpreted patient data into manuscript. SLB enrolled participants. BB analysed and interpreted patient data into figures and tables using Microsoft Excel. BB helped collect patient data in various forms, including patient consent and helped enrol participants. SD generated random allocation sequences and assigned participants to interventions. WN was one of the clinical investigators and aided in data collection. NM performed informed consent and gathered clinical data. APN analysed and interpreted patient data into figures and tables utilizing Microsoft Excel and Microsoft Word. MDP was vital in assisting with draft revisions and helped create the study design. SY and SN proofread and edited the manuscript. SN edited and revised the tables and graphs. All authors read and approved the final manuscript. Funding No funding received for this study Data availability The datasets used and/or analysed during the current study and the full trial protocol are available from the corresponding author on reasonable request. Ethics approval and consent to participate Ethics approval for this study has been obtained from the Institutional Review Board of Kennesaw State University under the FDA and DHHS (OHRP) designation of category 1a - Clinical study of drugs and medical devices for which investigational new drug application is not required. Informed Consent: Informed consent was obtained from all subjects before their participation in the study. Participants received clear and comprehensive information regarding the study's purpose, procedures, potential risks and benefits, confidentiality measures, and their right to withdraw at any time without consequences. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests in this section. 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A systematic review of prospective studies in unselected patients. BMJ Open. 2012;2(1):e000435; doi:10.1136/bmjopen-2011-000435. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 23 Oct, 2024 Read the published version in BMC Musculoskeletal Disorders → Version 1 posted Editorial decision: Revision requested 20 Aug, 2024 Reviews received at journal 18 Aug, 2024 Reviewers agreed at journal 14 Aug, 2024 Reviews received at journal 12 Aug, 2024 Reviewers agreed at journal 04 Aug, 2024 Reviewers invited by journal 02 Aug, 2024 Editor invited by journal 30 Jul, 2024 Editor assigned by journal 25 Jul, 2024 Submission checks completed at journal 25 Jul, 2024 First submitted to journal 25 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Yamasaki","email":"","orcid":"","institution":"Enso Medical Technologies Inc","correspondingAuthor":false,"prefix":"","firstName":"Dwayne","middleName":"S.","lastName":"Yamasaki","suffix":""},{"id":342483479,"identity":"d44ff24c-7c14-4442-bdfb-e45b794bbdf8","order_by":8,"name":"Scott Nickerson","email":"","orcid":"","institution":"NE Wyoming Wound Care Clinic","correspondingAuthor":false,"prefix":"","firstName":"Scott","middleName":"","lastName":"Nickerson","suffix":""}],"badges":[],"createdAt":"2024-07-25 14:10:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4802432/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4802432/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12891-024-07972-3","type":"published","date":"2024-10-23T15:57:30+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":63371809,"identity":"6e653d7b-a628-4ed2-bf18-8f58e54c3e67","added_by":"auto","created_at":"2024-08-27 11:59:52","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":36598,"visible":true,"origin":"","legend":"\u003cp\u003eFlow Chart of Study Enrolment\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4802432/v1/5b8e39b332ab9ea3b544d542.jpg"},{"id":63370613,"identity":"0e359e17-4c46-4cdb-a783-5787c605ad07","added_by":"auto","created_at":"2024-08-27 11:51:52","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":27521,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in EHL Muscle strength of CFN-supplied foot and ankle muscles after 0.3 cc injections of lidocaine\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4802432/v1/7b3ebb79ee26bdf7bc3d077f.jpg"},{"id":63370612,"identity":"8df8a7e0-1ac9-4ab9-97dc-780ed78fa098","added_by":"auto","created_at":"2024-08-27 11:51:52","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":30421,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in EHL Muscle strength of CFN supplied foot and ankle muscles after 0.3 cc injections of Papaverine\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4802432/v1/ae1b51d592d86cd8675985bf.jpg"},{"id":63370610,"identity":"23f4fab1-9c4c-489d-9626-1a8bf0a8c8d9","added_by":"auto","created_at":"2024-08-27 11:51:52","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":69210,"visible":true,"origin":"","legend":"\u003cp\u003eClinical and Ultrasonic representation of Common Fibular Nerve Block\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4802432/v1/0673b29acd723503422ce0d0.jpg"},{"id":67682588,"identity":"50fd0cd4-8065-42c6-a1ca-fa3ca9b3d8cd","added_by":"auto","created_at":"2024-10-28 16:14:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":619685,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4802432/v1/4f2d3a5e-8766-47fb-bd26-f3f2a74db65f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Is the Phoenix Sign Phenomenon Due to Vasodilation? A Double-Blinded, Randomized Controlled Trial Comparing Motor Function Recovery After Diagnostic Common Fibular Nerve Block with Lidocaine and Papaverine","fulltext":[{"header":"1 Background","content":"\u003cp\u003eEntrapment of the common fibular nerve (CFN) at the level of the fibular neck in the lower extremity is the most commonly recognized peripheral nerve entrapment in the lower extremity [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. It can cause chronic lower extremity pain, abnormal sensation, or motor weakness. Due to variations of clinical presentation, and comorbidities such as low back pain, recognition and diagnosis of this pathology can be complicated.\u003c/p\u003e \u003cp\u003eEarly diagnosis and treatment can prevent or mitigate musculoskeletal and neurological sequelae that can occur with delay in treatment [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. One of the consequences of CFN entrapment is Drop Foot, due to a paralysis of the muscles of the anterior and lateral compartment of the leg. However, Drop Foot can have other causes, such as traumatic injury, rapid weight loss in bariatric surgery, positioning during or after knee and hip surgery, herniation of a lumbar disc, intraneural ganglia, long periods of squatting, and metabolic conditions causing neural oedema and enlargement such as type II diabetes [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Local lidocaine injection is used clinically to test whether pain relief may be expected after neurolysis. Recent literature reports that patients with Drop Foot can gain motor strength after an injection of a minimal volume of 1% lidocaine adjacent to the CFN [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. After the injection, an effect was seen where the patient would temporarily regain partial or full dorsiflexion. This is named the Phoenix Sign. A positive Phoenix sign is helpful in the diagnosis and assessment of CFN palsy, allowing the clinician to reliably identify a focal peripheral nerve compression. Anaesthetic infiltration is placed adjacent to the CFN under sonographic guidance in patients with complete drop foot or significantly weakened motor strength of the muscles of the anterior compartment of the leg (Extensor Hallucis Longus (EHL), Tibialis Anterior (TA), and Extensor Digitorum Longus (EDL). This brief, lidocaine-induced improvement of anterior compartment muscle strength can allow the clinician to reliably differentiate a focal peripheral nerve compression from a CNS or more central peripheral nerve aetiology. There has been much conjecture about the explanation of this observation. Might this phenomenon be due to some type of neural reflex from the local anaesthetic agent, or could it be simply due to the vasodilatory effect of lidocaine? This study was designed to examine whether the Phoenix Effect produced by lidocaine and the known vasodilator papaverine were comparable.\u003c/p\u003e"},{"header":"2 Methods","content":"\u003cp\u003e A double-blinded, randomised, prospective controlled trial was conducted at US Neuropathy Centers in Marietta, GA, under the approval of the Kennesaw State University Institutional Review Board. Patients with weak dorsiflexion of the ankle or a drop foot were recruited from the existing clinical practice at US Neuropathy Centers. Cohort inclusion criteria also included a stable medical and medication status, ages 18\u0026ndash;85, speaking English as the primary language, and ambulatory. Walking aids or ankle-foot orthosis were permitted. Baseline characteristics of the 2 groups are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (Show gender, cohort age ranges, pertinent medical diagnosis or history). Based on the inclusion criteria, only 20 patients were enrolled (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Patients were recruited over a period of 1 year and two months from January 2021 to March 2022 with no requirement for follow-up. The enrollment was concluded due to this being a pilot study.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePatient demographics with gender, cohort age ranges, and pertinent medical history\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSubject\u003c/p\u003e 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colname=\"c3\"\u003e \u003cp\u003e39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFibromyalgia\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCervical spinal fusion\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePolyneuropathy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTarsal Tunnel\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eObese\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCMT\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSleep apnoea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDiabetes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncomplete Paraplegia\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDiabetes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eChronic Pain\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eChronic pain\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSmall Fiber Neuropathy Restless leg syndrome\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDiabetes PVD\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDiabetes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLumbar Pain\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNeuropathy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eChronic pain (hx of MVA)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePeripheral Neuropathy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePlantar fasciitis\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLumbar Radiculopathy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLumbar Radiculopathy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDiabetes\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePAD\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePeripheral Neuropathy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePeripheral Neuropathy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e Participants were randomised by the throw of dice to injection of 0.3 cc of Papaverine HCl 10 mg/mL or 0.3 cc of 1% Lidocaine HCl adjacent to CFN in a room separate from patient room. Injection solutions were prepared by non-blinded assistants and were visually indistinguishable. Patients and physicians are blinded to drugs received. Motor strength of the Extensor Hallucis Longus (EHL), Tibialis Anterior (TA), and Extensor Digitorum Longus (EDL) muscles were tested. Strength was rated according to the Medical Research Council Manual Muscle Testing scale 0\u0026ndash;5. The CFN at the fibular neck was identified under high-resolution ultrasound imaging. The injection site was prepared with alcohol, and ethyl chloride was used to anaesthetise the skin. A 30-gauge 1-inch needle was inserted adjacent to, but not within, the CFN and 0.3cc of drug delivered (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The investigator then waited approximately five minutes and re-tested motor strength of the Extensor Hallucis Longus (EHL), Tibialis Anterior (TA), and Extensor Digitorum Longus (EDL) muscles manually.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3 Results","content":"\u003cp\u003eThe baseline and post-injection muscle strength of TA, EHL and EDL was rated as 0 to 5 according to the Medical Research Council Manual Muscle Testing scale as in Ciesla, et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Post-injection strength was tested after 4\u0026ndash;6 minutes. EHL, TA, and EDL strength before and after papaverine or lidocaine injections is reported for all subjects. EHL showed the most consistent and severe baseline weakness but improved in every subject and regained full power in 9/11 of lidocaine subjects and 6/9 of papaverine subjects (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e and 3). Baseline TA strength was normal in greater than half the cases. EDL baseline strength was lower, but all achieved full strength after injection but one case. One subject had a history of Charcot Marie Tooth (CMT) disease. CMT subject was an outlier, showing no improvements in any muscle but EHL and even then, just 1 level from muscle recovery 1 to 2 strength after papaverine injection (see Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChanges in MMT strength of CFN supplied foot and ankle muscles after injection of lidocaine or papaverine vasodilator drug\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMuscle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eDrug\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eMMT Mean Strength\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eRegained any strength\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eRegained 5/5 strength\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eP value\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePre\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePost\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChange\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eEHL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLidocaine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e11 / 11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9 / 11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePapaverine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e9 / 9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6 / 9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLidocaine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3 / 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3 / 11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePapaverine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4 / 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4 / 9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eEDL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLidocaine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e11 / 11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e11 / 11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePapaverine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7 / 8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7 / 9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e "},{"header":"4 Discussion","content":"\u003cp\u003eAccurate diagnosis of lower extremity peripheral nerve entrapments can be difficult even for the most experienced clinicians. When there may be coexisting pathology such as previous CNS disturbances like stroke and multiple sclerosis or low back pathology, a simple diagnosis becomes more complicated.\u003c/p\u003e \u003cp\u003eInterestingly, we have seen patients who have a documented history of a CNS pathology that demonstrated a positive Phoenix Sign. Universally, this small cohort of patients who subsequently underwent nerve decompression surgery enjoyed improved muscle strength, indicating the patient had to have had a \u0026ldquo;double-crush\u0026rdquo;, two-pathology presentation [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] with at least some substantive nerve compression of the CFN at the neck of the fibula. Otherwise, post-operative improvements would not have been seen. These observations reinforce the potential value of this diagnostic nerve block in patients suffering from CFN palsy who also have documented CNS pathology. The accurate diagnosis will be missed or delayed in many cases if the Phoenix sign is not sought, leaving patients with a condition that could have been treated successfully with peripheral nerve decompression surgery. This would make recovery of better or normal musculoskeletal function in a high percentage of cases less likely [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOur findings presented in this paper strongly support the vasodilation hypothesis as explaining the Phoenix Sign. Both plain lidocaine and papaverine produced temporary restoration of motor function.\u003c/p\u003e \u003cp\u003eWhile there is a paucity of literature regarding the efficacy of diagnostic peripheral nerve block to predict surgical outcomes, Dr. Nirenberg published an important paper in 2020 demonstrating similar diagnostic findings where he injected 4 cc of 1% plain lidocaine into the fibularis (peroneus) longus muscle belly adjacent to where the common fibular nerve courses around the neck of the fibula [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. His hypothesis \u0026ldquo;...that the peroneus longus muscle becomes flaccid or relaxed, to an extent, allowing compression of the muscle (and its underlying fascia band) on the CFN to lessen, reducing and/or eliminating the nerve entrapment.\u0026rdquo; Our findings did not support his hypothesis of muscle relaxation as the mechanism behind his clinical observations because our administration of lidocaine was always below 0.5 cc (a miniscule amount that empirically could not be believed to cause significant muscular relaxation even if administered into the muscle) and was not infiltrated intramuscularly. Additionally, the musculature had increased motor strength 4 minutes after infiltration, which would not be expected from a muscle that is rendered flaccid. While papaverine is known to have some small indirect effects on smooth muscle, our administration of it was not intramuscular, and the same increase in motor strength was observed after its administration, as was seen with the patients that received lidocaine. Regardless of the hypothesis proffered by Nirenberg\u0026rsquo;s work, it does demonstrate the ability to assist in the verification of a focal nerve entrapment of the common fibular nerve and gives prognostic insight correlative to what we have observed with the Phoenix Sign.\u003c/p\u003e \u003cp\u003eIn their rat model of chronic nerve compression, MacKinnon and Dellon [11] showed that at approximately 6 months post compression of the sciatic nerve, a very significant level of nerve degeneration can be seen histologically, and that after decompression, even in the presence of diabetes, the peripheral nerve can regenerate. Secondary nerve regeneration has been understood and well documented by Zhong et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and Juckett et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Uemura and colleagues [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e14\u003c/span\u003e] in 2021 have demonstrated increased vascular circulation around the tibial nerve in diabetic neuropathic patients after tarsal tunnel decompression surgery. Specifically, they showed a thirty percent increase in vascularity around the tibial nerve illustrating how improvement in nerve function is related to improvement in vascularity. Anderson et al reinforce this fact in their study which demonstrated functional improvement of muscles in the leg via intraoperative EMG following CFN decompression in patients with diabetic neuropathy. Almost 43% of both fibularis longus and TA muscles regained strength from baseline in one leg. The return of microcirculation via the decompression of vasa nervorum along with CFN was attributed to the rapid functional improvement in muscles although the authors\u0026rsquo; study was not designed for this type of investigation [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDrop Foot is a commonly seen complication following knee and hip replacement surgery. Kremers et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e16\u003c/span\u003e] reported that by 2010 there had been 4.7\u0026nbsp;million total knee arthroplasties and 2.5\u0026nbsp;million hip replacements performed. Estimates of CFN complications following hip arthroplasty are 0.44% and post- knee arthroplasty range from 0.3\u0026ndash;1.3% [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. It is possible that these percentages are underestimated, as Beswick et al. showed a much higher incidence of chronic post-surgical pain of 10\u0026ndash;34% following knee arthroplasty and 7\u0026ndash;23% following hip arthroplasty procedures [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. It is generally believed that peripheral nerve injury, especially to the CFN, makes up the lion\u0026rsquo;s share of these postoperative complications [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. With extrapolation of the lower estimates, the incidence of drop foot or post arthroplasty pain due to CFN injury could comprise a significant percentage of the 124,100 to 721,000 cases annually.\u003c/p\u003e"},{"header":"5 Limitations of the study","content":"\u003cp\u003eThe purpose of this study was simply to determine whether a small local injection of the vasodilator papaverine exhibited an objective temporary increase in motor strength as does 1% lidocaine. Our results show it does, confirming that local circulation restoration can be a part of focal CFN dysfunction. This study had a small cohort size, but the result is significant by statistical analysis. Further investigation confirming the result with a larger number of subjects would be ideal.\u003c/p\u003e \u003cp\u003eThe study cohort is quite heterogeneous in diagnoses, yet the Phoenix sign correctly predicted motor improvement in all but the Charcot-Marie-Tooth subject. The double blinded, randomized, prospective design of this study is a strength despite the small sample size. A larger number of subjects would be ideal. Additionally, there is always a question of subject heterogeneity/homogeneity within the subject group. The purpose of this study was simply to determine if the papaverine group exhibited an increase in motor strength similar to that as seen within the lidocaine group when these medications were delivered at the site of a focal nerve compression. Focal nerve compression can be independent of any antecedent or concurrent medical comorbidities and the fact that there was some medical diversity within the subject group showed the universality of effect of the diagnostic blocks.\u003c/p\u003e"},{"header":"6 Conclusion","content":"\u003cp\u003eBased on the results seen, there is no statistical difference in the increase of motor strength for the dorsiflexors after either infiltration with lidocaine or papaverine. These findings, although it is a small cohort, strongly suggest that the phenomenon known as the Phoenix Sign is due to the vasodilation component of the infiltrated local anaesthetic, and not some other unknown neurological explanation. With proper dosage and technique of ultrasound guided infiltration, the findings from this diagnostic block can provide the clinician with improved diagnostic accuracy of CFN entrapment.\u003c/p\u003e \u003cp\u003eAdditionally, the patient who demonstrates a positive Phoenix sign has a very high likelihood of successful peripheral nerve surgical decompression.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCFN\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eCommon Fibular Nerve\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEHL\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eExtensor Hallucis Longus\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eTA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eTibialis Anterior\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEDL\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eExtensor Digitorum Longus\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMMT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eManual Muscle Testing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCNS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eCentral Nervous System\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHeather Stein, Ph.D. helped with preparing the manuscript and supporting documents for final submission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSLB is the primary author and major contributor in writing the manuscript as well as interpreted patient data into manuscript. SLB enrolled participants. BB analysed and interpreted patient data into figures and tables using Microsoft Excel. BB helped collect patient data in various forms, including patient consent and helped enrol participants. SD generated random allocation sequences and assigned participants to interventions.\u0026nbsp;WN was one of the clinical investigators and aided in data collection. NM performed informed consent and gathered clinical data. APN analysed and interpreted patient data into figures and tables utilizing Microsoft Excel and Microsoft Word. MDP was vital in assisting with draft revisions and helped create the study design. SY and SN proofread and edited the manuscript. SN edited and revised the tables and graphs. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding received for this study\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study and the full trial protocol are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthics approval for this study has been obtained from the Institutional Review Board of Kennesaw State University under the FDA and DHHS (OHRP) designation of category 1a - Clinical study of drugs and medical devices for which investigational new drug application is not required.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent:\u003c/strong\u003e Informed consent was obtained from all subjects before their participation in the study. Participants received clear and comprehensive information regarding the study\u0026apos;s purpose, procedures, potential risks and benefits, confidentiality measures, and their right to withdraw at any time without consequences.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests in this section.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBowley MP, Doughty CT. Entrapment Neuropathies of the Lower Extremity. Med Clin North Am. 2019;103(2):371\u0026ndash;82; doi:10.1016/j.mcna.2018.10.013.\u003c/li\u003e\n\u003cli\u003ePark JH, Yang J, Park KR, Kim TW, Kim T, Park S, Tsengel B, Cho J. A Cadaveric Study of the Distal Biceps Femoris Muscle in relation to the Normal and Variant Course of the Common Peroneal Nerve: A Possible Cause of Common Peroneal Entrapment Neuropathy. Biomed Res Int. 2020;2020:3093874; doi:10.1155/2020/3093874.\u003c/li\u003e\n\u003cli\u003eSouter J, Swong K, McCoyd M, Balasubramanian N, Nielsen M, Prabhu VC. Surgical Results of Common Peroneal Nerve Neuroplasty at Lateral Fibular Neck. World Neurosurg. 2018;112:e465\u0026ndash;72; doi:10.1016/j.wneu.2018.01.061.\u003c/li\u003e\n\u003cli\u003eMadani S, Doughty C. Lower extremity entrapment neuropathies. Best Pract Res Clin Rheumatol. 2020;34(3):101565; doi:10.1016/j.berh.2020.101565.\u003c/li\u003e\n\u003cli\u003eFortier LM, Markel M, Thomas BG, Sherman WF, Thomas BH, Kaye AD. An Update on Peroneal Nerve Entrapment and Neuropathy. Orthop Rev (Pavia). 2021;13(2):24937; doi:10.52965/001c.24937.\u003c/li\u003e\n\u003cli\u003eBarret SL, Khan A, Brown V, Rosas E, Du Casse S, Bailey P. Predictive Reliability of the Phoenix Sign for the Outcome of Common Fibular (Peroneal) Nerve Decompression Surgery. Open J Orthop. 2020;10(9):234\u0026ndash;40; doi:10.4236/ojo.2020.109025.\u003c/li\u003e\n\u003cli\u003eCiesla N, Dinglas V, Fan E, Kho M, Kuramoto J, Needham D. Manual muscle testing: a method of measuring extremity muscle strength applied to critically ill patients. J Vis Exp. 2011;(50):2632; doi:10.3791/2632.\u003c/li\u003e\n\u003cli\u003eUpton AR, McComas AJ. The double crush in nerve entrapment syndromes. Lancet. 1973;2(7825):359\u0026ndash;62; doi:10.1016/s0140-6736(73)93196-6.\u003c/li\u003e\n\u003cli\u003eKaneda T, Hayasaka R, Nagai Y, Tajima T, Urakawa N, Nakajyo S, Shimizu K. Effects of Papaverine on Twitches in Mouse Diaphragm. Pharmacology. 2010;86(5\u0026ndash;6):273\u0026ndash;80; doi:10.1159/000320769.\u003c/li\u003e\n\u003cli\u003eNirenberg MS. A simple test to assist with the diagnosis of common fibular nerve entrapment and predict outcomes of surgical decompression. Acta Neurochir (Wien). 2020;162(6):1439\u0026ndash;44; doi:10.1007/s00701-020-04344-3.\u003c/li\u003e\n\u003cli\u003eMackinnon SE, Dellon AL, Hudson AR, Hunter DA. Chronic nerve compression\u0026ndash;an experimental model in the rat. Ann Plast Surg. 1984;13(2):112\u0026ndash;20; doi:10.1097\u003cbr\u003e /00000637-198408000-00004.\u003c/li\u003e\n\u003cli\u003eZhong W, Yang M, Zhang W, Visocchi M, Chen X, Liao C. Improved neural microcirculation and regeneration after peripheral nerve decompression in DPN rats. Neurol Res. 2017;39(4):285\u0026ndash;91; doi:10.1080/01616412.2017.1297557.\u003c/li\u003e\n\u003cli\u003eJuckett L, Saffari TM, Ormseth B, Senger JL, Moore AM. The Effect of Electrical Stimulation on Nerve Regeneration Following Peripheral Nerve Injury. Biomolecules. 2022;12(12):1856; doi:10.3390/biom12121856.\u003c/li\u003e\n\u003cli\u003eUemura T, Watanabe H, Yanai T, Kawano H, Yoshida A, Okutsu I. A Minimally Invasive Full Endoscopic Approach to Tibial Nerve Neurolysis in Diabetic Foot Neuropathy: An Alternative to Open Procedures. Plast Reconstr Surg. 2021;148(3):592\u0026ndash;96; doi:10.1097/PRS.0000000000008299.\u003c/li\u003e\n\u003cli\u003eAnderson JC, Nickerson DS, Tracy BL, Paxton RJ, Yamasaki DS. Acute improvement in intraoperative EMG following common fibular nerve decompression in patients with symptomatic diabetic sensorimotor peripheral neuropathy: 1. EMG results. J Neurol Surg A Cent Eur Neurosurg. 2017;78(5):419\u0026ndash;30; doi:10.1055/s-0036-1593958.\u003c/li\u003e\n\u003cli\u003eMaradit KH, Larson DR, Crowson CS, Kremers WK, Washington RE, Steiner CA, Jiranek WA, Berry DJ. Prevalence of Total Hip and Knee Replacement in the United States. J Bone Joint Surg Am. 2015;97(17):1386\u0026ndash;97; doi:10.2106/JBJS.N.01141.\u003c/li\u003e\n\u003cli\u003eWengler A, Nimptsch U, Mansky T. Hip and knee replacement in Germany and the USA: Analysis of individual inpatient data from German and US hospitals for the years 2005 to 2011. Dtsch Arztebl Int. 2014; 111(23\u0026ndash;24):407\u0026ndash;16; doi:10.3238/arztebl.2014.0407.\u003c/li\u003e\n\u003cli\u003eBeswick AD, Wylde V, Gooberman-Hill R, Blom A, Dieppe P. What proportion of patients report long-term pain after total hip or knee replacement for osteoarthritis? A systematic review of prospective studies in unselected patients. BMJ Open. 2012;2(1):e000435; doi:10.1136/bmjopen-2011-000435.\u003c/li\u003e\n\u003c/ol\u003e\n"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Drop Foot, vascular perfusion, peripheral nerve block, common peroneal nerve, peripheral nerve","lastPublishedDoi":"10.21203/rs.3.rs-4802432/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4802432/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eFocal entrapment of the common fibular (peroneal) nerve (CFN) is the most common nerve entrapment in the lower extremity. Accurate diagnosis can be difficult due to co-existent pathology such as low back pathology. A 1% lidocaine block of CFN is often used to confirm the local entrapment pathology and demonstrate possibility of pain relief. A surprising, unexpected and temporary strengthening of CFN supplied ankle and foot muscles is occasionally produced, termed the Phoenix sign. Aetiology of this phenomenon has been puzzling, but restoration of neural circulation and nutrition via improved local blood flow has been postulated to be responsible.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eThis is a double-blinded, randomized, prospective controlled trial of 19 patients, comparing 2 vasodilating agents and their ability to produce the Phoenix effect. Ultrasound guided infiltration of 0.3 mL 1% lidocaine or papaverine HCl 10 mg/mL was executed adjacent to CFN. Motor strength pre- infiltration and 4 minutes post-infiltration were measured for anterior compartment muscles utilizing MRC manual motor testing reported on a 0\u0026ndash;5 scale. The extensor hallucis longus (EHL) muscle proved to be the most significant.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eAverage motor strength of the EHL improved from 2.2 (+/-0.40) to 4.9 (+/-0.32).) in the lidocaine group. In the papaverine group, pre-infiltration EHL motor strength averaging 2.1 (+/-0.93) improved to 4.4 (+/- 1.01) post-infiltration. Papaverine and lidocaine produced similar statistically significant increases in muscle strength (p\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThere was no difference between small local infiltrations of lidocaine or papaverine in production of increased anterior compartment EHL motor strength. It is most likely that the Phoenix Effect is explained by temporary local improvements in the microcirculation of the CFN vasa nervorum.\u003c/p\u003e","manuscriptTitle":"Is the Phoenix Sign Phenomenon Due to Vasodilation? A Double-Blinded, Randomized Controlled Trial Comparing Motor Function Recovery After Diagnostic Common Fibular Nerve Block with Lidocaine and Papaverine","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-08-27 11:51:47","doi":"10.21203/rs.3.rs-4802432/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-08-20T06:37:55+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-18T09:16:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"182142701859248429392683303642779882952","date":"2024-08-14T14:33:07+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-08-13T02:04:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"210039625521962513930846376018003541736","date":"2024-08-04T10:27:54+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-08-02T10:17:39+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-07-30T20:44:32+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-26T03:26:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-26T03:25:55+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Musculoskeletal Disorders","date":"2024-07-25T14:08:37+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"6c35f1c9-14f5-4c97-89f4-4b86af3d907a","owner":[],"postedDate":"August 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-10-28T16:10:28+00:00","versionOfRecord":{"articleIdentity":"rs-4802432","link":"https://doi.org/10.1186/s12891-024-07972-3","journal":{"identity":"bmc-musculoskeletal-disorders","isVorOnly":false,"title":"BMC Musculoskeletal Disorders"},"publishedOn":"2024-10-23 15:57:30","publishedOnDateReadable":"October 23rd, 2024"},"versionCreatedAt":"2024-08-27 11:51:47","video":"","vorDoi":"10.1186/s12891-024-07972-3","vorDoiUrl":"https://doi.org/10.1186/s12891-024-07972-3","workflowStages":[]},"version":"v1","identity":"rs-4802432","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4802432","identity":"rs-4802432","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}