An ‘Invisible Nerve’ To Block: A Regional Anaesthesia Block Conundrum of Sciatic Nerve for Above-Knee Amputation in A High-Risk Patient

An ‘Invisible Nerve’ To Block: A Regional Anaesthesia Block Conundrum of Sciatic Nerve for Above-Knee Amputation in A High-Risk Patient | 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 Case Report An ‘Invisible Nerve’ To Block: A Regional Anaesthesia Block Conundrum of Sciatic Nerve for Above-Knee Amputation in A High-Risk Patient Malaka Munasinghe Baththirange, NJASS Jayasuriya This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5639461/v2 This work is licensed under a CC BY 4.0 License Status: Posted Version 2 posted You are reading this latest preprint version Show more versions Abstract Background Above-knee amputation (AKA) under regional anaesthesia alone can pose multiple challenges to anaesthetists. For AKA, ultrasound-guided selective sciatic nerve, posterior femoral cutaneous nerve (PFCN), femoral, lateral femoral cutaneous, and obturator nerve blockade provide satisfactory anaesthesia. Here, we present probably the first reported case of liquefactive necrosis of the sciatic nerve leading to a challenging subgluteal block. Case Presentation A 52-year-old woman with ischemic heart disease, atrial fibrillation on therapeutic anticoagulation, chronic kidney disease stage 3, poorly controlled diabetes mellitus, anaemia, and heart failure (ejection fraction 25–30%) was scheduled for an urgent left AKA under regional anaesthesia block due to ascending infection. Considering the high risk, a suprainguinal fascia iliaca block with a perineural catheter was performed under ultrasound. Visualisation of the sciatic nerve and the PFCN was unsuccessful as the neurosonoanatomy was undetectable. The motor response using a nerve stimulator to the suspected sciatic nerve failed, too. 0.375% levobupivacaine 20ml was administered in the area of the suspected nerves using piriformis and other sonoanatomical landmarks. Amputation was carried out without additional analgesia or sedation. Intraoperatively, the sciatic nerve was found to be distorted macroscopically due to liquefactive necrosis. Postoperatively in HDU, her pain control was satisfactory with perineural infusion. Conclusions The inability to identify the sciatic nerve due to liquefaction is a peculiar encounter in this patient. Still, it hints at an unusual cause for difficult peripheral nerve visualisation and stimulation. Due to the fact that the sciatic and PFCN lie closer when they exit the sciatic foramen under piriformis, a sufficient volume of local anaesthetic during sciatic nerve block may spread around and anaesthetise PFCN. Above-knee amputation regional nerve block sciatic nerve posterior femoral cutaneous nerve liquefactive necrosis case report Figures Figure 1 Figure 2 Introduction Above-knee amputation (AKA) is associated with increased perioperative mortality and morbidity [1]. The majority of the patients have multiple co-morbidities and are on polypharmacy, including antiplatelets and anticoagulants [2]. These factors will play an essential role in deciding the mode of anaesthesia. Regional nerve blocks are emerging as a safer, more practical, and effective alternative to standard methods. They offer the additional advantage of continued postoperative analgesia with the use of perineural catheters [3]. This case report presents a challenging and distinctive case of regional anaesthesia in a middle-aged woman where other modes of anaesthesia offered a high risk and presents probably the first documented case of liquefactive necrosis of sciatic nerve found during subgluteal sciatic nerve block. It was presented as an eposter (P147) at the 41st European Society of Regional Anaesthesia, Prague, 2024. Case Report A 52-year-old Caucasian woman, American Society of Anaesthesiology Physical Status 3, weight 75 kg and body mass index 20kgm − 2 , presented to the vascular unit of our institution with an ascending wound infection in her left leg, with a recent history of repeated wound debridement. Her past medical history included ischemic heart disease, atrial fibrillation, chronic kidney disease stage 3, poorly controlled diabetes mellitus, anaemia, and heart failure (ejection fraction 25–30%). Past surgical history included peripheral occlusive arterial disease. She did not disclose any history of allergy. She was a chronic, heavy smoker (40 pack years) and an occasional alcoholic. She was on a therapeutic dose of enoxaparin. Her vital parameters were as follows. Non-invasive blood pressure was 92/54mmHg; pulse rate was 102 per minute; peripheral oxygen saturation was 93% on room air; and respiratory rate was 20 per minute. Her initial haemoglobin was 68g/L. Two units of packed red blood cells were transfused slowly overnight under frusemide cover, which raised her haemoglobin to 83g/L. Her C-reactive protein was elevated (345 mg/dl) with a white cell count of 25,000/mm 3 . The clotting profile was normal. Serum electrolytes were normal. Creatinine was 1.2mg/dl. Her random blood sugar was 245mg/dl. She was started on sliding-scale insulin infusion and broad-spectrum antibiotics after taking blood and urine for cultures. Her echocardiogram showed sinus tachycardia and no other abnormalities. Arterial blood gas analysis revealed metabolic acidosis (pH 7.30 PCO2 31 PO2 98 (on air), bicarbonate 16 BE -8 lactate 3.7). Considering the high risk for thrombosis, preoperative therapeutic enoxaparin was continued. Consent was taken to proceed with the above-knee amputation of the septic left leg under the regional nerve block with a high-dependency bed reserved for postoperative care. A suprainguinal fascia iliaca (SIFI) block was performed under ultrasound guidance with 20 ml of 0.5% levobupivacaine and 10 ml of 2% lignocaine 1:200,000 adrenaline (Fig. 1 ). A perineural catheter was placed successfully. The patient was positioned in a lateral position. Attempts at ultrasonic visualisation of the sciatic nerve and posterior femoral cutaneous nerve (PFCN) along their course failed. Nerve stimulation was also attempted using the landmark technique. A motor response was not elicited after careful needle placement. Under ultrasonic guidance, using piriformis as the reference, 0.375% levobupivacaine 20ml was deposited in the anatomical region of the nerves. No paresthesia was detected during the whole procedure. The plan in case of insufficient analgesia during the posterior dissection was to administer intravenous short-acting opiates and local infiltration of 2% lignocaine. After 20 minutes following the completion of the block, satisfactory cutaneous analgesia was achieved in the required dermatomes. Intraoperatively, a guillotine amputation was performed, and the patient was comfortable without requiring additional analgesia. During the dissection, it was found that the sciatic nerve had undergone liquefactive necrosis (Fig. 2 ). Due to the local infection, the surgeon did not place a sciatic nerve perineural catheter. Arterial blood pressure monitoring was continued with a small dose of peripheral phenylephrine infusion (500 mic/hr.). In the high-dependency unit, perineural infusion was continued with 0.2% Ropivacaine 15ml/hr with excellent pain relief. Her phenylephrine infusion was weaned off overnight. She was sent to the ward on day two of the postoperative period. Consent was obtained from the patient before the manuscript was written. Discussion For complete surgical anaesthesia for AKA, the femoral, lateral femoral cutaneous nerve, obturator nerve, and posterior femoral cutaneous nerve (PFCN) territories should be anaesthetised. The posterior femoral cutaneous nerve is a small sensory nerve [4]. Selective block of this nerve is possible under ultrasound guidance but might prove challenging [5]. The obturator nerve provides cutaneous supply to the medial aspect of the thigh, making it necessary to anaesthetise before AKA. SIFI block aids the anaesthesia of the femoral, lateral femoral cutaneous nerve and obturator nerve. Despite the controversy over the reliable block of the obturator nerve during SIFI, it is noted that a higher volume of local anaesthetic can, in fact, block the obturator nerve satisfactorily [6–7]. An RCT conducted to assess the obturator nerve block during SIFI had shown an 86% success rate [8]. Using nerve catheters and long-acting local anaesthetic agents has further increased the efficacy of fascial iliaca compartment blocks during AKA by lengthening postoperative analgesia [9]. Sciatic nerve block at the gluteal region is adopted for AKA by anaesthetists. This may aid in blocking PFCN due to the proximity of both at the greater sciatic foramen under the piriformis muscle when they exit. At the level of transgluteal or subgluteal sciatic block, two nerves lie in different compartments, requiring separate injections to block each [10]. However, an adequate volume of local anaesthetic deposited around the sciatic nerve at this level might spread proximally and anaesthetise the smaller diameter PFCN. The evidence is lacking in this regard as studies have shown that the deep investing muscular fascia acts as a barrier to local anaesthetic spread between the nerves [11]; thus, the probability of the former postulation needs to be researched. It should be noted that intramuscular injection of local anaesthetics should be avoided to prevent myotoxicity [12]. Liquefaction of the sciatic nerve is an interesting (and infrequent) occurrence witnessed in our patient. The increased severity of the underlying infection might have contributed to it. The clinical implications were the difficulty visualising the nerve under ultrasound and the failed electrical stimulation despite its normal anatomical position confirmed during dissection. The inability of ultrasonic detection may be due to tissue oedema, which reduces the echo contrast between the nerve and the adjacent structures due to co-existent infection [13]. The macroscopic and microscopic destruction of the nerve filaments may have led to failed electrical stimulation. It is unclear whether the infection involved the PFCN, as it was not identified during the dissection. The surrounding necrotic tissue and the relatively acidic environment might act similarly to a peripheral local anaesthetic infiltration in the case of a block of a larger peripheral nerve. This is an exciting area to explore. Studies have shown that the local anaesthetic doses required in patients with diabetic neuropathy are comparatively less [14–15]. Patients with organ failure are at a higher risk of local anaesthetic systemic toxicity [16]. On the contrary to these observations, we opted for higher doses (in the background of diabetes, renal failure and heart failure). The patient was at high cardiac risk during the AKA with a background history of ischemic heart disease and atrial fibrillation, where suboptimal perioperative pain control would have precipitated a major adverse cardiac event. As providing other anaesthetic modes was impractical, the sole mode of anaesthesia was regional nerve blockade. To complicate the matter, she was extremely anxious as well. The patient was continuously monitored during the intraoperative period (with the use of ultrasound during SIFI block and the use of a local anaesthetic agent with reduced systemic toxicity, levobupivacaine) and postoperative period in the HDU for any local anaesthetic-related adverse event, including systemic toxicity. Thus, we opted for relatively higher doses (not exceeding toxic doses) under close, continued monitoring to ensure satisfactory anaesthesia during the intraoperative period and extended analgesia during the postoperative period. In conclusion, we presented an extremely rare occurrence of sciatic nerve liquefaction in a patient who underwent AKA. Such presentations will provide a challenging case of peripheral nerve blockade for a nerve block enthusiast. Abbreviations Above-knee amputation AKA Suprainguinal fascia iliaca SIFI Posterior femoral cutaneous nerve PFCN Declarations Competing Interests: The authors declare no conflicts of interest. Running Head Sciatic nerve block conundrum due to liquefactive necrosis Ethics approval and consent to participate: Our institution does not require ethical approval to publish anonymised case reports on patient identity. Consent for publication The patient provided written informed consent for the publication of this case report and accompanying images. The editor-in-chief of this journal can review a copy of the written consent upon request. Competing interests The authors declare no conflicts of interest. Funding Not applicable Funding: The authors have no sources of funding to declare for this manuscript. Author Contribution BMM, NJ- Concept, literature review, preparation of initial manuscript, critical analysis, Approval of the final manuscript Acknowledgement The authors want to acknowledge Dr V. Parameswaran and Dr Athmaja Thottungal (Consultant Anaesthetists, Kent and Canterbury Hospital, Canterbury CT1 3NG, United Kingdom) for their clinical supervision and manuscript revision, respectively. Availability of data and materials Data sharing does not apply to this article as no datasets were generated or analysed during the current study. References 1. Chandran R, Beh ZY, Tsai FC, Kuruppu SD, Lim JY. Peripheral nerve blocks for above-knee amputation in high-risk patients. Journal of Anaesthesiology Clinical Pharmacology. 2018 Oct 1;34(4):458 − 64. 2. Kujak MK, Pomerantz LH, Petrovic M. Regional technique provides complete surgical anesthesia for above-the-knee amputation: a viable alternative to general endotracheal anesthesia in a time of COVID-19. Cureus. 2022 May;14(5). 3. Neil MJ. Pain after amputation. Bja Education. 2016 Mar 1;16(3):107 − 12. 4. Saba EK. Posterior femoral cutaneous nerve sensory conduction study in a sample of apparently healthy Egyptian volunteers. The Egyptian Journal of Neurology, Psychiatry and Neurosurgery. 2022 Dec 15;58(1):162. 5. Meng S, Lieba-Samal D, Reissig LF, Gruber GM, Brugger PC, Platzgummer H, Bodner G. High-resolution ultrasound of the posterior femoral cutaneous nerve: visualization and initial experience with patients. Skeletal radiology. 2015 Oct;44:1421-6. 6. Bendtsen TF, Pedersen EM, Moriggl B, Hebbard P, Ivanusic J, Børglum J, Nielsen TD, Peng P. Anatomical considerations for obturator nerve block with fascia iliaca compartment block. Reg Anesth Pain Med. 2021 Sep;46(9):806–812 7. Amato PE, Thames MR. How I do it: suprainguinal fascia iliaca block. ASRA News 2020;45. https://doi.org/10.52211/asra110120.063 8. Desmet M., Vermeylen K., Van Herreweghe I. A longitudinal supra-inguinal fascia iliaca compartment block reduces morphine consumption after total hip arthroplasty. Reg Anesth Pain Med. 2017;42:327–333 9. O'Reilly N, Desmet M, Kearns R. Fascia iliaca compartment block. BJA Educ. 2019 Jun;19(6):191–197 10. Feigl GC, Schmid M, Zahn PK, González CA, Litz RJ. The posterior femoral cutaneous nerve contributes significantly to sensory innervation of the lower leg: an anatomical investigation. British Journal of Anaesthesia. 2020 Mar 1;124(3):308 − 13. 11. Johnson CS, Johnson RL, Niesen AD, Stoike DE, Pawlina W. Ultrasound-guided posterior femoral cutaneous nerve block: a cadaveric study. Journal of Ultrasound in Medicine. 2018 Apr;37(4):897–903. 12. Hussain N, McCartney CJ, Neal JM, Chippor J, Banfield L, Abdallah FW. Local anaesthetic-induced myotoxicity in regional anaesthesia: a systematic review and empirical analysis. British Journal of Anaesthesia. 2018 Oct 1;121(4):822 − 41 13. Henderson M, Dolan J. Challenges, solutions, and advances in ultrasound-guided regional anaesthesia. BJA Education. 2016 Nov 1;16(11):374 − 80. 14. Parthasarathy S, Chanda A, Saravanan B. Estimation of the minimum effective volume of 0.5% bupivacaine for ultrasound-guided popliteal sciatic nerve block in diabetic patients with neuropathy. Indian J Anaesth. 2022 Jul;66(7):511–516 15. Kumar TS, Indu K, Parthasarathy S. Successful Management of above Knee Amputation with Combined and Modified Nerve Blocks. Anesth Essays Res. 2017 Apr-Jun;11(2):520–521 16. Mahajan A, Derian A. Local Anesthetic Toxicity. [Updated 2022 Oct 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499964/ Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 2 posted You are reading this latest preprint version Show more versions 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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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5639461","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":430104498,"identity":"547ee329-0365-11f0-91e4-06cc9d20a69f","order_by":0,"name":"Malaka Munasinghe Baththirange","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4ElEQVRIiWNgGAWjYFAC5gbGBgY5Bgb2BiDHwIIYLYwgLcYMDDwHQFokSNEikQDiEaFFt/1g48cZNQbR5pLPr274USDBwN/enYBXi9mZxGbJDccMcnfOzim72QN0mMSZsxvwazmQ2CD5gO1P7obbOWk3eIBaDCRyCWg5/7D554N/Brkbbp5Ju/mHKC03EtskN7YBtdxgP3abOFtuPGyznNkH9EtPDtttGQMJHsJ+OZ98+GbPN4Pc7ezHn91888dGjr+9F78WODBg4DEA0TzEKYdoYX9AvOpRMApGwSgYUQAASmtQqyCnKzsAAAAASUVORK5CYII=","orcid":"","institution":"Base Hospital, Thambuththegama","correspondingAuthor":true,"prefix":"","firstName":"Malaka","middleName":"Munasinghe","lastName":"Baththirange","suffix":""},{"id":430104499,"identity":"5e66a71a-0365-11f0-91e4-06cc9d20a69f","order_by":1,"name":"NJASS Jayasuriya","email":"","orcid":"","institution":"Base Hospital, Thambuththegama","correspondingAuthor":false,"prefix":"","firstName":"NJASS","middleName":"","lastName":"Jayasuriya","suffix":""}],"badges":[],"createdAt":"2024-12-13 16:08:24","currentVersionCode":2,"declarations":"","doi":"10.21203/rs.3.rs-5639461/v2","doiUrl":"https://doi.org/10.21203/rs.3.rs-5639461/v2","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":78702340,"identity":"95245e9c-abbe-422f-b920-73d587004973","added_by":"auto","created_at":"2025-03-17 19:44:49","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":241987,"visible":true,"origin":"","legend":"\u003cp\u003eUltrasound-guided suprainguinal fascia iliaca block\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5639461/v2/0561bec4abff4dcb31ddca91.jpg"},{"id":78702019,"identity":"465699f6-4c53-4814-9ca1-9c4ba7b05cc0","added_by":"auto","created_at":"2025-03-17 19:36:49","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":940607,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of the intraoperative finding of the liquefied Sciatic nerve (Real-time image was not acquired due to technical difficulties)\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5639461/v2/7886d754092d8150de6ce164.jpg"},{"id":83105618,"identity":"6ce67c8d-b9ad-43df-9329-537213f12b1a","added_by":"auto","created_at":"2025-05-20 06:09:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1555067,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5639461/v2/8172553d-ebf7-43e4-aba2-dc6e4211e5d1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"An ‘Invisible Nerve’ To Block: A Regional Anaesthesia Block Conundrum of Sciatic Nerve for Above-Knee Amputation in A High-Risk Patient","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAbove-knee amputation (AKA) is associated with increased perioperative mortality and morbidity [1]. The majority of the patients have multiple co-morbidities and are on polypharmacy, including antiplatelets and anticoagulants [2]. These factors will play an essential role in deciding the mode of anaesthesia. Regional nerve blocks are emerging as a safer, more practical, and effective alternative to standard methods. They offer the additional advantage of continued postoperative analgesia with the use of perineural catheters [3]. This case report presents a challenging and distinctive case of regional anaesthesia in a middle-aged woman where other modes of anaesthesia offered a high risk and presents probably the first documented case of liquefactive necrosis of sciatic nerve found during subgluteal sciatic nerve block. It was presented as an eposter \u003cb\u003e(P147)\u003c/b\u003e at the 41st European Society of Regional Anaesthesia, Prague, 2024.\u003c/p\u003e"},{"header":"Case Report","content":"\u003cp\u003eA 52-year-old Caucasian woman, American Society of Anaesthesiology Physical Status 3, weight 75 kg and body mass index 20kgm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, presented to the vascular unit of our institution with an ascending wound infection in her left leg, with a recent history of repeated wound debridement. Her past medical history included ischemic heart disease, atrial fibrillation, chronic kidney disease stage 3, poorly controlled diabetes mellitus, anaemia, and heart failure (ejection fraction 25\u0026ndash;30%). Past surgical history included peripheral occlusive arterial disease. She did not disclose any history of allergy. She was a chronic, heavy smoker (40 pack years) and an occasional alcoholic. She was on a therapeutic dose of enoxaparin. Her vital parameters were as follows. Non-invasive blood pressure was 92/54mmHg; pulse rate was 102 per minute; peripheral oxygen saturation was 93% on room air; and respiratory rate was 20 per minute. Her initial haemoglobin was 68g/L. Two units of packed red blood cells were transfused slowly overnight under frusemide cover, which raised her haemoglobin to 83g/L. Her C-reactive protein was elevated (345 mg/dl) with a white cell count of 25,000/mm\u003csup\u003e3\u003c/sup\u003e. The clotting profile was normal. Serum electrolytes were normal. Creatinine was 1.2mg/dl. Her random blood sugar was 245mg/dl. She was started on sliding-scale insulin infusion and broad-spectrum antibiotics after taking blood and urine for cultures. Her echocardiogram showed sinus tachycardia and no other abnormalities. Arterial blood gas analysis revealed metabolic acidosis (pH 7.30 PCO2 31 PO2 98 (on air), bicarbonate 16 BE -8 lactate 3.7). Considering the high risk for thrombosis, preoperative therapeutic enoxaparin was continued. Consent was taken to proceed with the above-knee amputation of the septic left leg under the regional nerve block with a high-dependency bed reserved for postoperative care.\u003c/p\u003e \u003cp\u003eA suprainguinal fascia iliaca (SIFI) block was performed under ultrasound guidance with 20 ml of 0.5% levobupivacaine and 10 ml of 2% lignocaine 1:200,000 adrenaline (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA perineural catheter was placed successfully. The patient was positioned in a lateral position. Attempts at ultrasonic visualisation of the sciatic nerve and posterior femoral cutaneous nerve (PFCN) along their course failed. Nerve stimulation was also attempted using the landmark technique. A motor response was not elicited after careful needle placement. Under ultrasonic guidance, using piriformis as the reference, 0.375% levobupivacaine 20ml was deposited in the anatomical region of the nerves. No paresthesia was detected during the whole procedure. The plan in case of insufficient analgesia during the posterior dissection was to administer intravenous short-acting opiates and local infiltration of 2% lignocaine. After 20 minutes following the completion of the block, satisfactory cutaneous analgesia was achieved in the required dermatomes. Intraoperatively, a guillotine amputation was performed, and the patient was comfortable without requiring additional analgesia. During the dissection, it was found that the sciatic nerve had undergone liquefactive necrosis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDue to the local infection, the surgeon did not place a sciatic nerve perineural catheter. Arterial blood pressure monitoring was continued with a small dose of peripheral phenylephrine infusion (500 mic/hr.). In the high-dependency unit, perineural infusion was continued with 0.2% Ropivacaine 15ml/hr with excellent pain relief. Her phenylephrine infusion was weaned off overnight. She was sent to the ward on day two of the postoperative period. Consent was obtained from the patient before the manuscript was written.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eFor complete surgical anaesthesia for AKA, the femoral, lateral femoral cutaneous nerve, obturator nerve, and posterior femoral cutaneous nerve (PFCN) territories should be anaesthetised. The posterior femoral cutaneous nerve is a small sensory nerve [4]. Selective block of this nerve is possible under ultrasound guidance but might prove challenging [5]. The obturator nerve provides cutaneous supply to the medial aspect of the thigh, making it necessary to anaesthetise before AKA. SIFI block aids the anaesthesia of the femoral, lateral femoral cutaneous nerve and obturator nerve. Despite the controversy over the reliable block of the obturator nerve during SIFI, it is noted that a higher volume of local anaesthetic can, in fact, block the obturator nerve satisfactorily [6\u0026ndash;7]. An RCT conducted to assess the obturator nerve block during SIFI had shown an 86% success rate [8]. Using nerve catheters and long-acting local anaesthetic agents has further increased the efficacy of fascial iliaca compartment blocks during AKA by lengthening postoperative analgesia [9].\u003c/p\u003e \u003cp\u003eSciatic nerve block at the gluteal region is adopted for AKA by anaesthetists. This may aid in blocking PFCN due to the proximity of both at the greater sciatic foramen under the piriformis muscle when they exit. At the level of transgluteal or subgluteal sciatic block, two nerves lie in different compartments, requiring separate injections to block each [10]. However, an adequate volume of local anaesthetic deposited around the sciatic nerve at this level might spread proximally and anaesthetise the smaller diameter PFCN. The evidence is lacking in this regard as studies have shown that the deep investing muscular fascia acts as a barrier to local anaesthetic spread between the nerves [11]; thus, the probability of the former postulation needs to be researched. It should be noted that intramuscular injection of local anaesthetics should be avoided to prevent myotoxicity [12].\u003c/p\u003e \u003cp\u003eLiquefaction of the sciatic nerve is an interesting (and infrequent) occurrence witnessed in our patient. The increased severity of the underlying infection might have contributed to it. The clinical implications were the difficulty visualising the nerve under ultrasound and the failed electrical stimulation despite its normal anatomical position confirmed during dissection. The inability of ultrasonic detection may be due to tissue oedema, which reduces the echo contrast between the nerve and the adjacent structures due to co-existent infection [13]. The macroscopic and microscopic destruction of the nerve filaments may have led to failed electrical stimulation.\u003c/p\u003e \u003cp\u003eIt is unclear whether the infection involved the PFCN, as it was not identified during the dissection. The surrounding necrotic tissue and the relatively acidic environment might act similarly to a peripheral local anaesthetic infiltration in the case of a block of a larger peripheral nerve. This is an exciting area to explore. Studies have shown that the local anaesthetic doses required in patients with diabetic neuropathy are comparatively less [14\u0026ndash;15]. Patients with organ failure are at a higher risk of local anaesthetic systemic toxicity [16]. On the contrary to these observations, we opted for higher doses (in the background of diabetes, renal failure and heart failure). The patient was at high cardiac risk during the AKA with a background history of ischemic heart disease and atrial fibrillation, where suboptimal perioperative pain control would have precipitated a major adverse cardiac event. As providing other anaesthetic modes was impractical, the sole mode of anaesthesia was regional nerve blockade. To complicate the matter, she was extremely anxious as well. The patient was continuously monitored during the intraoperative period (with the use of ultrasound during SIFI block and the use of a local anaesthetic agent with reduced systemic toxicity, levobupivacaine) and postoperative period in the HDU for any local anaesthetic-related adverse event, including systemic toxicity. Thus, we opted for relatively higher doses (not exceeding toxic doses) under close, continued monitoring to ensure satisfactory anaesthesia during the intraoperative period and extended analgesia during the postoperative period.\u003c/p\u003e \u003cp\u003eIn conclusion, we presented an extremely rare occurrence of sciatic nerve liquefaction in a patient who underwent AKA. Such presentations will provide a challenging case of peripheral nerve blockade for a nerve block enthusiast.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eAbove-knee amputation\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eAKA\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eSuprainguinal fascia iliaca\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eSIFI\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePosterior femoral cutaneous nerve\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePFCN\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting Interests:\u003c/h2\u003e \u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eRunning Head\u003c/h2\u003e \u003cp\u003eSciatic nerve block conundrum due to liquefactive necrosis\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eEthics approval and consent to participate:\u003c/h2\u003e\u003cp\u003eOur institution does not require ethical approval to publish anonymised case reports on patient identity.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003ch2\u003eConsent for publication\u003c/h2\u003e \u003cp\u003e The patient provided written informed consent for the publication of this case report and accompanying images. The editor-in-chief of this journal can review a copy of the written consent upon request.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eNot applicable\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThe authors have no sources of funding to declare for this manuscript.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eBMM, NJ- Concept, literature review, preparation of initial manuscript, critical analysis, Approval of the final manuscript\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors want to acknowledge Dr V. Parameswaran and Dr Athmaja Thottungal (Consultant Anaesthetists, Kent and Canterbury Hospital, Canterbury CT1 3NG, United Kingdom) for their clinical supervision and manuscript revision, respectively.\u003c/p\u003e\u003ch2\u003eAvailability of data and materials\u003c/h2\u003e \u003cp\u003eData sharing does not apply to this article as no datasets were generated or analysed during the current study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e1. Chandran R, Beh ZY, Tsai FC, Kuruppu SD, Lim JY. Peripheral nerve blocks for above-knee amputation in high-risk patients. Journal of Anaesthesiology Clinical Pharmacology. 2018 Oct 1;34(4):458\u0026thinsp;\u0026minus;\u0026thinsp;64.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e2. Kujak MK, Pomerantz LH, Petrovic M. Regional technique provides complete surgical anesthesia for above-the-knee amputation: a viable alternative to general endotracheal anesthesia in a time of COVID-19. Cureus. 2022 May;14(5).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e3. Neil MJ. Pain after amputation. Bja Education. 2016 Mar 1;16(3):107\u0026thinsp;\u0026minus;\u0026thinsp;12.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e4. Saba EK. Posterior femoral cutaneous nerve sensory conduction study in a sample of apparently healthy Egyptian volunteers. The Egyptian Journal of Neurology, Psychiatry and Neurosurgery. 2022 Dec 15;58(1):162.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e5. Meng S, Lieba-Samal D, Reissig LF, Gruber GM, Brugger PC, Platzgummer H, Bodner G. High-resolution ultrasound of the posterior femoral cutaneous nerve: visualization and initial experience with patients. Skeletal radiology. 2015 Oct;44:1421-6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e6. Bendtsen TF, Pedersen EM, Moriggl B, Hebbard P, Ivanusic J, B\u0026oslash;rglum J, Nielsen TD, Peng P. Anatomical considerations for obturator nerve block with fascia iliaca compartment block. Reg Anesth Pain Med. 2021 Sep;46(9):806\u0026ndash;812\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e7. Amato PE, Thames MR. How I do it: suprainguinal fascia iliaca block. ASRA News 2020;45. https://doi.org/10.52211/asra110120.063\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e8. Desmet M., Vermeylen K., Van Herreweghe I. A longitudinal supra-inguinal fascia iliaca compartment block reduces morphine consumption after total hip arthroplasty. Reg Anesth Pain Med. 2017;42:327\u0026ndash;333\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e9. O'Reilly N, Desmet M, Kearns R. Fascia iliaca compartment block. BJA Educ. 2019 Jun;19(6):191\u0026ndash;197\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e10. Feigl GC, Schmid M, Zahn PK, Gonz\u0026aacute;lez CA, Litz RJ. The posterior femoral cutaneous nerve contributes significantly to sensory innervation of the lower leg: an anatomical investigation. British Journal of Anaesthesia. 2020 Mar 1;124(3):308\u0026thinsp;\u0026minus;\u0026thinsp;13.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e11. Johnson CS, Johnson RL, Niesen AD, Stoike DE, Pawlina W. Ultrasound-guided posterior femoral cutaneous nerve block: a cadaveric study. Journal of Ultrasound in Medicine. 2018 Apr;37(4):897\u0026ndash;903.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e12. Hussain N, McCartney CJ, Neal JM, Chippor J, Banfield L, Abdallah FW. Local anaesthetic-induced myotoxicity in regional anaesthesia: a systematic review and empirical analysis. British Journal of Anaesthesia. 2018 Oct 1;121(4):822\u0026thinsp;\u0026minus;\u0026thinsp;41\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e13. Henderson M, Dolan J. Challenges, solutions, and advances in ultrasound-guided regional anaesthesia. BJA Education. 2016 Nov 1;16(11):374\u0026thinsp;\u0026minus;\u0026thinsp;80.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e14. Parthasarathy S, Chanda A, Saravanan B. Estimation of the minimum effective volume of 0.5% bupivacaine for ultrasound-guided popliteal sciatic nerve block in diabetic patients with neuropathy. Indian J Anaesth. 2022 Jul;66(7):511\u0026ndash;516\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e15. Kumar TS, Indu K, Parthasarathy S. Successful Management of above Knee Amputation with Combined and Modified Nerve Blocks. Anesth Essays Res. 2017 Apr-Jun;11(2):520\u0026ndash;521\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e16. Mahajan A, Derian A. Local Anesthetic Toxicity. [Updated 2022 Oct 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499964/\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Above-knee amputation, regional nerve block, sciatic nerve, posterior femoral cutaneous nerve, liquefactive necrosis, case report","lastPublishedDoi":"10.21203/rs.3.rs-5639461/v2","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5639461/v2","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eAbove-knee amputation (AKA) under regional anaesthesia alone can pose multiple challenges to anaesthetists. For AKA, ultrasound-guided selective sciatic nerve, posterior femoral cutaneous nerve (PFCN), femoral, lateral femoral cutaneous, and obturator nerve blockade provide satisfactory anaesthesia. Here, we present probably the first reported case of liquefactive necrosis of the sciatic nerve leading to a challenging subgluteal block.\u003c/p\u003e\u003ch2\u003eCase Presentation\u003c/h2\u003e \u003cp\u003eA 52-year-old woman with ischemic heart disease, atrial fibrillation on therapeutic anticoagulation, chronic kidney disease stage 3, poorly controlled diabetes mellitus, anaemia, and heart failure (ejection fraction 25\u0026ndash;30%) was scheduled for an urgent left AKA under regional anaesthesia block due to ascending infection. Considering the high risk, a suprainguinal fascia iliaca block with a perineural catheter was performed under ultrasound. Visualisation of the sciatic nerve and the PFCN was unsuccessful as the neurosonoanatomy was undetectable. The motor response using a nerve stimulator to the suspected sciatic nerve failed, too. 0.375% levobupivacaine 20ml was administered in the area of the suspected nerves using piriformis and other sonoanatomical landmarks. Amputation was carried out without additional analgesia or sedation. Intraoperatively, the sciatic nerve was found to be distorted macroscopically due to liquefactive necrosis. Postoperatively in HDU, her pain control was satisfactory with perineural infusion.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThe inability to identify the sciatic nerve due to liquefaction is a peculiar encounter in this patient. Still, it hints at an unusual cause for difficult peripheral nerve visualisation and stimulation. Due to the fact that the sciatic and PFCN lie closer when they exit the sciatic foramen under piriformis, a sufficient volume of local anaesthetic during sciatic nerve block may spread around and anaesthetise PFCN.\u003c/p\u003e","manuscriptTitle":"An ‘Invisible Nerve’ To Block: A Regional Anaesthesia Block Conundrum of Sciatic Nerve for Above-Knee Amputation in A High-Risk Patient","msid":"","msnumber":"","nonDraftVersions":[{"code":2,"date":"2025-03-17 19:28:44","doi":"10.21203/rs.3.rs-5639461/v2","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}},{"code":1,"date":"2025-01-16 09:01:44","doi":"10.21203/rs.3.rs-5639461/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2e99f508-7dae-49e3-b536-177414835a36","owner":[],"postedDate":"March 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-05-20T06:08:53+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-17 19:28:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v2","identity":"rs-5639461","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5639461","identity":"rs-5639461","version":["v2"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}