a 46-year - old female patient was admitted with complaints of severe pain and paresthetica in the right anterolateral femoral region , which started a month ago . at the time of admittance ,
the visual analog scale ( vas ) of the patient was 8 , and she complained of excruciating pain in the right femoral region when she started to walk , causing her to rest more than 5 minutes before walking again .
recently , she had even woken once or twice in the night from the pain in the right femoral region .
the patient had visited a private orthopedics hospital , but there were no abnormalities in the lumbar x - ray , and despite continual physical modalities , there were no improvements in symptoms . after careful history taking , it was found that she had a total thyroidectomy 8 months previous because of a thyroid mass , and after the procedure her weight increased 27 kg , from 67 kg to 94 kg . in the standing position
in the physical exam , the straight leg raising test was normal , there was numbness in the right lateral femoral region , and there were trigger points along the inguinal ligament that generated symptomatic pain when pressured . based on the past history and physical exam , meralgia paresthetica was suspected , so a lateral femoral cutaneous nerve block using ultrasound ( s - nerve , sonosite inc . ,
jelly was applied to the linear probe ( 13 - 6 hz ) and disinfected transparent plastic was draped .
the end of the linear probe was positioned at the anterior superior iliac spine ( asis ) , and in line with the inguinal ligament it was moved down and confirmed the lfcn located above the sartorius and below the tensor fasciae latae ( fig .
a 23 gauge , 60 mm needle was inserted facing the lateral from the medial side of the patient and positioned near the lfcn by monitoring the current position using ultrasound .
a mixture of 1:10,000 epinephrine 0.15 ml , 0.2% bupivacaine 9 ml , and triamcinolone acetonide 40 mg was injected around the nerve while monitoring medication diffusion with ultrasound . after injection , the patient was bed rested for 30 minutes and returned home without complications . in a visit a week later
, the patient 's vas had been reduced to 3 . using the same method as the first procedure
, the procedure was performed once more but with half the amount of bupivacaine and triamcinolone acetonide , that is 1:10,000 epinephrine 0.15 ml , 0.2% bupivacaine 5 ml , and triamcinolone acetonide 20 mg . a week after the second procedure , a medical examination was conducted over the telephone and the vas had decreased to 0 .
lateral femoral cutaneous nerve block for the treatment of meralgia paresthetica is a commonly known treatment method , but there were no reports of procedures using ultrasound in south korea .
hafer first presented meralgia paresthetica in 1885 , reporting pressure on the lateral femoral cutaneous nerve as cause for the pain . from the greek words meros ( thigh ) and algos ( pain ) , roth named it " meralgia paresthetica " in 1895 , which has been used up to the present time .
meralgia paresthetica is characterized by pain and paresthica along the lfcn and is caused by compression of the nerves from conditions that increase intra - abdominal pressure such as obesity , pregnancy , tight belts or pants , metabolic disorders ( diabetes ) , alcohol and lead poisoning , or damage from surgeries near the inguinal region because of anatomical variability of the lfcn .
obesity is considered to be the reason in our case since there was a recent 27 kg increase in body weight .
the lfcn is a pure sensory nerve that originates from the 2 , 3 lumbar nerves emerges from the side of the psoas major and passes the iliacus diagonally towards the asis .
it then passes above , below or between the inguinal ligament , above the sartorius and into the subcutaneous tissue of the femoral region .
then it is divided into anterior and posterior division : the front controls the frontal femoral region and up to the knee area , the rear controls the lateral femoral region up to the greater trochanter area .
the anatomical variability of the lfcn is about 30% , and according to reports of bjurlin et al .
, the distance from the asis to the lfcn can vary from 0.3 - 6.5 cm .
however , blind blocks have had a failure rate of more than 60% and there could be blockages of the femoral or obturator nerve or intra - abdominal insertion .
nerve stimulators can reportedly increase the success rate up to 85% , but their use doubles the time needed and results can vary depending on the patient 's subjective complaints of paresthetica .
recently , ultrasound usage has increased dramatically in the area of pain medicine since it can confirm the target nerve and surrounding structures to allow accurate diagnosis , reduce additional damage when injecting medication , and allow injection of steroids or local anesthetic agents in the exact location .
ng et al .   investigated whether ultrasound was an accurate tool to find the location of the lfcn in 20 cadavers and 10 volunteers .
the location of the lfcn found through anatomical landmarks of 2.5 cm interior and 2.5 cm below the asis was compared with the location of the lfcn found using ultrasound .
accuracy was confirmed by dissection of the cadavers , and location of the actual nerve was confirmed by using the transdermal nerve stimulators in the volunteers .
location accuracy using anatomical landmarks was 5.3% in cadavers and 0% in volunteers , while accuracy of the ultrasound was 84.2% in cadavers and 80% in volunteers .
this study demonstrated how inaccurate blind block according to anatomical landmarks can be due to anatomical variance of the lfcn , while highlighting the accuracy of ultrasound - guided procedures .
from the three cases , two showed successful results , and the procedure was performed 4 and 3 times , respectively , for the 2 cases .
although the type of local anesthesia used was different , since our case obtained effective treatment results with less local anesthesia in two procedures , it can be suggested that ultrasound - guided blockage of the lfcn is more effective than results from blind technique .
it is commonly known that the amount of local anesthetic agent used is reduced in ultrasound - guided nerve blocks .
when blocking the lfcn , the amount of local anesthetic agent used in blind blocks is no less than 30 ml , while in ultrasound - guided lfcn blocks , usually 10 to 15 ml is recommended .
hurdle et al .   also reported a 100% success rate in ultrasound - guided blockage of the lfcn in 10 patients with small anesthetic dosages of 1 ml to 8 ml .
reducing the amount of local anesthetic agent used can reduce systemic toxicity as well as the risk of unintended blockage of the femoral or obturator nerves .
one week after the second procedure was performed , there were improvements in the vas and no complaints of sensory impairment or motor weakness in unintended areas , despite using half the amount of local anesthetic agent compared to the first procedure .
this effective result without unintended blocks was from accurate injection using ultrasound despite the small amount of local anesthetic agent used compared to blind blockage .
future research regarding minimum dosage of local anesthetic agent required when performing ultrasound - guided blockage of lfcn will be necessary .
 meralgia paresthetica is a rarely encountered sensory mononeuropathy characterized by paresthesia , pain or sensory impairment along the distribution of the lateral femoral cutaneous nerve ( lfcn ) caused by entrapment or compression of the nerve as it crossed the anterior superior iliac spine and runs beneath the inguinal ligament . 
 there is great variability regarding the area where the nerve pierces the inguinal ligament , which makes it difficult to perform blind anesthetic blocks . 
 ultrasound has developed into a powerful tool for the visualization of peripheral nerves including very small nerves such as accessory and sural nerves . 
 the lfcn can be located successfully , and local anesthetic solution distribution around the nerve can be observed with ultrasound guidance . 
 our successfully performed ultrasound - guided blockade of the lfcn in meralgia paresthetica suggests that this technique is a safe way to increase the success rate . 
CASE REPORT
DISCUSSION