comparing ways to freeze the nerve that provides thigh sensation

Conditions: Meralgia Paresthetica

Summary: background the sensation on the outside of portion of our thighs is provided by a nerve called the lateral femoral cutaneous nerve (lfcn). the investigators can inject freezing around the nerve to reduce the feeling around the thigh (i.e. anesthesia). anesthesia, or freezing, of the lateral femoral cutaneous nerve can reduce pain for patients having a) hip and knee surgery \[1,2\], b) removal of a skin graft \[3\], and c) wound care. in addition, damage to the lfcn (i.e. meralgia paresthetica) has been associated with body armour and gun belt use in military and police personnel \[4\]. although generally a benign condition, compression or injury to this nerve can be painful and require treatment. in addition, the actual variability in sensory distribution for this nerve has not been elucidated in a topographical fashion and will be measured in this study. finding the most efficient and effective method for anesthesia of the lfcn can improve and positively impact the quality of pain control for patients. ultrasound has improved the accuracy and efficiency of various other regional anesthesia techniques, and could also impact the safety. therefore the investigators hypothesize that ultrasound guided lateral femoral cutaneous nerve block using the subinguinal technique will be statistically more efficacious and efficient when compare to neurostimulation based blockade.

purpose of the study: the goal of this study is to compare the ultrasound-guided subinguinal injection technique to the neurostimulation-guided injection technique for lateral femoral cutaneous nerve block. the neurostimulation technique uses an electrical field to stimulate the nerve when a needle is close proximity. one older study showed it is better than using landmarks in achieving anesthesia of the lateral femoral cutaneous nerve, but no studies have compared it to using ultrasound to freeze the nerve \[7\]. the primary outcome will be relative efficiency, i.e. the total anesthesia-related time (defined as the sum of performance and onset times). this is looking at how long it takes for the procedure (needle insertion, medication injection), plus the time it takes for the thigh to go numb. secondary outcomes will include relative success rate, procedural discomfort, number of needle passes and topographical sensory distribution of this nerve in this cohort of patients . methodology: selection of human subjects: with the approval of the defence research \& development canada human research ethics committee (hrec), a total of 27 volunteers will be recruited. subjects will be recruited by advertising within the cf health services centre facility and by email notification to cf members in the national capital region through the dwan. if there is insufficient volunteers, those people that have volunteered, will be contacted by email to inquire if they are aware of any other people that maybe be interested in volunteering so that the study can be finalized. if they know if anyone, they will be asked to forward the initial email to those people, asking them to contact the investigator if they wish to have more information. interested civilian volunteers and class "a" reservists will be approached from the cohort of patients that responded to the original communication email. once patients have submitted their names for consideration, they will be contacted to review whether they meet inclusion/exclusion criteria. data analyses: the investigators expect the success rates to be similar for both groups. however our hypothesis is that the performance time and the onset time could be different. therefore the main outcome is the total anesthesia-related time (sum of performance and onset times). according to shannon et al \[7\], the total anesthesia-related time for the neurostimulation technique is 10.1 +/- 4.7 min (performance time: 9.5 +/- 4.7 min and onset time: 0.8 +/- 0.9 min). using a paired t-test to compare both techniques, a difference of 30% in total anesthesia time would represent an effect size of 0.74 and require a total of 17 subjects undergoing bilateral blocks to obtain a 2-tailed α error of 0.05 and a ß error of 0.2. since onset and total anesthesia-related times can only be measured for successful blocks and since the investigators expect a success rate of 85% for neurostimulation, the investigators will recruit 25 patients to account for those who do not reach the postulated end point. normality of the continuous data will first be assessed with the kolmogorov-smirnov test. continuous data will then analyzed using a paired t-test. for categorical data, the mann-whitney u test and chi-square test will be used as appropriate. hypotheses tested will be 2-tailed. p \< 0.05 will be considered statistically significant. risks: participation in this study will be voluntary and volunteers can withdraw consent at any time without having any effect on access to future medical care. there will likely minor discomfort during the procedure similar to having freezing before a dental procedure or blood drawn. patients can ask us to stop the procedure at any time. the chance of minor discomfort for up to a day or two after the injection can occur and can be managed with over the counter acetaminophen or ibuprofen. the investigators do not expect any limitations to daily activities. furthermore, side effects associated with lateral femoral cutaneous nerve blocks have not been reported and are likely rare. \[8\]. confidentiality/anonymity patients' confidentiality/anonymity will be protected through two mechanisms: * research subjects are identified by serial numbers * access to patient's research data will be restricted to primary investigators only approximate time involvement the approximate time commitment is 1.5 hour. roles and responsibilities of research team recruitment, study planning and organization will be done by gaurav gupta. technical procedures, data collection and manuscript preparation will be shared tasks by the entire research team.

Eligibility criteria:
inclusion criteria: * male and female between 18 and 60 years old * american society of anesthesiologists classification 1-3 exclusion criteria: * adults who are unable to give their own consent * pre-existing neuropathy (assessed by history and physical examination) - * coagulopathy (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. platelets ≤ 100, international normalized ratio ≥ 1.4 or prothrombin time ≥ 50) * renal failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. creatinine ≥ 100) * hepatic failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. transaminases ≥ 100) * allergy to local anesthetic agents local anesthetic * pregnancy based on patient self report of last menstrual cycle. if a patient wish/insist on participating in the study, and pregnancy status is unclear, a urine pregnancy test will be offered. also risk of lidocaine in pregnancy will be discussed with the patient as currently classified. we will convey that this risk is currently classified as a risk class b, which means that animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women. we will also discuss that animal-reproduction studies have shown an decrease in maternal fertility), but that was not confirmed in controlled studies in women in the first trimester and there is no evidence of a risk in later trimesters, * prior surgery in the hip and lateral leg region * prior lumbar surgery * previous pelvic fracture * previous l1, l2 or l3 lumbar radiculopathy, plexopathy or meralgia paresthetica * chronic pain syndromes requiring opioid intake

Keywords: lateral femoral cutaneous nerve block meralgia parasthetica nerve stimulator ultrasound