Femoral nerve block procedure guide

INTRODUCTION — The femoral nerve block (FNB) anesthetizes the anterior portion of the upper leg and medial portions of the lower leg. This block may be used to provide analgesia or surgical anesthesia for surgery of the upper leg and knee, for femoral neck and femur fractures, and for surgery of the medial calf, ankle, or foot. This topic will discuss the anatomy and injection techniques relevant to ultrasound guided and nerve stimulator guided femoral block.

General considerations common to all peripheral nerve blocks, including patient preparation and monitoring, use of aseptic technique, localization techniques, drug choices, contraindications, and complications, are discussed separately. (See "Overview of peripheral nerve blocks".)

Ultrasound guidance for peripheral nerve blocks is also discussed in detail separately. (See "Ultrasound for peripheral nerve blocks".) For all procedures, the use of a time-out or standard verification procedure prior to needle insertion is strongly encouraged.

ANATOMY — The femoral nerve is the largest terminal branch of the lumbar plexus and is derived from the ventral rami of L2-L4 spinal nerves (figure 1) [1].

Course of the nerve — After dividing off the lumbar plexus, the femoral nerve passes caudally in a groove between the psoas and iliacus muscles before adopting a position 1 to 2 cm lateral to the femoral artery at the level of the inguinal ligament. At the level of the inguinal crease the nerve remains lateral to the femoral artery but assumes a closer and occasionally posterolateral position. It then divides into anterior (superficial) and posterior (deep) branches (figure 2).

The fascia lata lies superficial to both the femoral vessels and femoral nerve at the level of the inguinal crease. In contrast, the fascia iliaca is deeper and immediately superficial to the femoral nerve. As the fascia iliaca courses medially, it lies between the femoral nerve and the femoral vessels. Whether the fascia iliaca encases the femoral nerve or instead lies just superficial to it is debated. Nonetheless, if local anesthetic is visualized spreading superficial to the artery during ultrasound guided block, it may indicate an inappropriately shallow needle position (movie 1).

The common femoral artery travels along with the femoral nerve before splitting into two branches, the deep and superficial branches, typically near or distal to the inguinal crease.

Innervation

●The anterior cutaneous branches of the femoral nerve provide sensory innervation to the skin of the anterior upper leg/thigh. The posterior division of the femoral nerve continues as the saphenous nerve, which supplies sensory innervation of the medial lower leg (figure 2 and figure 3).

●Osseous innervation of the femoral nerve predominately includes the pelvis, hip, anterior femur, patella, and medial proximal and distal tibia.

The femoral nerve innervates the medial and lateral hip capsule and anterior/anterolateral components of the hip joint [2]. The hip receives innervation widely from both the lumbar and sacral plexus.

The femoral nerve supplies the majority of innervation of the knee joint. There are also contributions from the sciatic, lateral femoral cutaneous, and obturator nerves. (See "Anesthesia for total knee arthroplasty", section on 'Relevant nerve and muscle anatomy'.)

●The femoral nerve supplies motor innervation to the sartorius, iliacus, pectineus, and quadriceps muscles (rectus femoris, vastus intermedius, vastus lateralis, and vastus medialis) [3]. Quadriceps contraction is used as the indicator for correct needle placement during nerve stimulator guided block. (See 'Nerve stimulation guided technique' below.) Of note, there is no motor innervation from the femoral to any muscle below the knee.

CLINICAL IMPLICATIONS OF ANATOMY — Femoral nerve blocks may be used for analgesia for the surgery or injury of the hip, femur, knee, and the medial lower leg. However, for complete anesthesia at these sites, other nerves (obturator, sciatic, lateral femoral cutaneous) must be blocked as well (figure 4). The role of femoral nerve block for these indications is discussed separately. (See "Anesthesia for orthopedic trauma", section on 'Anesthesia for lower extremity trauma' and "Anesthesia for total knee arthroplasty", section on 'Choice of peripheral nerve block'.)

The "3 in 1 block" is a term that was historically used to describe the performance of a femoral nerve block, with the idea that a single injection would anesthetize the lateral femoral cutaneous and obturator nerves in addition to the femoral nerve. The concept was based on the purported existence of a fascial sheath that enveloped the femoral nerve and could act as a conduit to the obturator nerve and lumbar plexus [4]. However, multiple studies have failed to replicate early success achieving blockade of these three nerves with a single injection, or the existence of a sheath conduit [5,6]. Therefore, alternative techniques (eg, targeted obturator and lateral femoral cutaneous blocks, lumbar plexus block, or suprainguinal and/or infrainguinal fascia iliaca blocks) should be used if block of the lateral femoral cutaneous and obturator nerves is required.

PATIENT POSITIONING — Position the patient supine and flat with the head of the bed lowered to a neutral position.

The clinician must have access to the inguinal crease to perform the block. For patients with obesity and a pendulous abdomen, it may be necessary to have an assistant retract the abdomen, or to tape the abdomen towards the contralateral side.

ULTRASOUND GUIDANCE VERSUS NERVE STIMULATOR GUIDANCE — We use ultrasound guidance to perform femoral nerve blocks. Ultrasound allows the clinician to verify the correct spread of local anesthetic and may reduce the risk of vascular puncture.

When ultrasound is not available, nerve stimulation is a reasonable alternative. Nerve stimulation may also be used for nerve confirmation during ultrasound-guided block, and should be used if the nerve cannot be visualized. Nerve stimulation can confirm the needle position and may serve as a monitor for needle contact with the nerve, potentially reducing the incidence of intraneural injection. (See "Overview of peripheral nerve blocks", section on 'Nerve stimulator guidance'.)

Studies that have compared ultrasound guidance versus nerve stimulator guidance have found similar block efficacy and increased block procedure time with nerve stimulation, whether used alone or in combination with ultrasound [7-9]. In one up and down sequential dose finding study that compared ultrasound guidance with nerve stimulator guidance in 60 patients who underwent knee arthroscopy, the effective dose of local anesthetic in 95 percent of cases was approximately 42 percent less with ultrasound guidance (22 [95% CI 13-36] versus 41 [95% CI 24-66] mL) [10].

ULTRASOUND GUIDED TECHNIQUE

●Select a linear high frequency transducer (eg, 15 to 5 mHz) (picture 1), with the depth set at approximately 3 cm. (See "Ultrasound for peripheral nerve blocks", section on 'Transducers'.)

●Place the transducer on the anterior leg transverse to the femur at the level of the inguinal crease (picture 2 and picture 3).

●Scan as follows: (image 1)

•Identify the femoral artery.

•Lateral to the femoral artery, identify the iliopsoas muscle.

•Identify the fascia iliaca, which covers the iliopsoas muscle and lies deep to the femoral artery and vein. In some cases, it may be difficult to visualize medial components of the fascia iliaca as it curves deep along the muscle and is therefore not angled towards the transducer.

•Identify the fascia lata superficial to the femoral artery and vein medially. This superficial position relative to the artery and vein differentiates the fascia lata from the fascia iliaca.

•Identify the femoral nerve. It appears as a hyperechoic structure lateral to the femoral artery, immediately deep to the fascia iliaca, and superficial to the iliopsoas muscle.

NOTE: Lymph notes are common in the groin and can be mistaken for femoral nerve, but they are generally more superficial and would NOT be deep to fascia iliaca.

•If the deep and superficial branches of the femoral artery are visualized, move the transducer cephalad until they coalesce into a single structure (the common femoral artery) (image 2).

•Attempt to optimize the image of the femoral nerve by tilting the ultrasound probe, applying additional probe pressure, or implementing small rotational/rocking/sliding probe adjustments (figure 5).

●Slide the probe laterally until the femoral artery is located on the medial portion of the screen. This position will allow for a decreased angle of incidence and improved block needle visualization.

●Use color Doppler to confirm the absence of significant vasculature in the path of the block needle (movie 2).

●Insert a short bevel (30°) 5 to 10 cm 22-gauge needle using an in-plane or out-of-plane ultrasound approach, visualizing the needle tip throughout (picture 4).

•For an in plane approach, insert the needle in a lateral to medial direction, 1 to 2 cm lateral to the edge of the transducer.

•For an out of plane approach, insert the needle at the midpoint of the transducer at a steep angle, advancing with hydrodissection or staccato needle movements to detect tissue deflection.

●Advance the needle tip to a position beneath the fascia iliaca and lateral to the femoral nerve. A pop may be felt as the needle tip passes through the fascia iliaca.

●Nerve stimulation can be used to confirm needle tip placement as described below. (See 'Nerve stimulation guided technique' below.)

●After negative aspiration, hydrodissect with a small volume of LA (eg, 3 to 5 mL) to visualize separation of the fascia iliaca from the nerve. Scan proximally and distally to confirm spread of LA along the femoral nerve (image 3). Continue to inject a total of 10 to 20 mL of LA, with gentle aspiration between injections, visualizing spread along the nerve.

Note: Local anesthetic spreading superficial to the femoral artery may indicate an injection that is inappropriately superficial to the fascia iliaca, and therefore not adjacent to the femoral nerve. If this occurs, stop the injection and reinsert the needle at a steeper angle, positioning the tip deep to the fascia iliaca before injecting again (movie 1).

●Reposition the needle as needed to optimize spread.

●Stop injection and reposition the needle tip if the patient complains of pain or paresthesia, if injection of local anesthetic is not visualized (potentially indicating an intravascular injection), if turbulent flow is detected in a vascular structure, or if there is resistance to injection. If using an injection pressure monitoring device, limit injection pressure to <15 pounds per square inch.

NERVE STIMULATION GUIDED TECHNIQUE — Nerve stimulator guidance can be used when ultrasound is not available, or along with ultrasound guidance when the nerve cannot be confidently visualized. We perform nerve stimulator guided block as follows, inserting the needle at the level of the inguinal crease and using a single stimulation assessed with quadriceps contraction. A more proximal approach at the level of the inguinal ligament has been described. However, at the inguinal crease the nerve is wider and more superficial and therefore easier to target [11].

A triple injection nerve stimulation technique targeting distinct muscle groups (vastus intermedius, vastus lateralis, and vastus medialis) has been described and may modestly improve analgesia and shorten block onset time, at the expense of prolonged block procedure time [12].

●The author uses a nerve stimulator initially set to a pulse width of 100 ms at 2 Hz and an initial current of 1.0 mA. We use an insulated, 30° (short) bevel, 20- to 22-gauge 5 to 10 cm stimulating needle. Connect the nerve stimulator to the needle and to an electrode placed on the patient's skin. (See "Overview of peripheral nerve blocks", section on 'Equipment for nerve stimulator guidance'.)

●Palpate the femoral artery at the level of or slightly distal to the inguinal ligament. At the level of the inguinal ligament, the femoral artery reliably lies at a midpoint position between the pubic symphysis and anterior superior iliac spine (picture 2 and figure 6). These landmarks can be helpful in patients with obesity, in whom there is a tendency to seek the femoral artery in a more lateral location.

●Insert the needle 1 cm lateral to the midpoint of the femoral artery pulse and 2 cm caudal to the inguinal ligament, angled slightly cephalad. This needle insertion point will be slightly distal to the inguinal crease (picture 5).

●Turn the stimulator on to 1 mA. Advance the needle until a quadriceps muscle response is induced, signified by a patellar twitch (picture 6).

•If a muscle twitch occurs with the medial thigh, the needle is positioned too medial and is stimulating motor branches to the sartorius muscle.

•If a localized motor response occurs near the site of needle insertion, the needle is likely directly stimulating the iliopsoas muscle and should be withdrawn and redirected.

•If no motor response if found, fan the needle systematically in a lateral or medial direction until an appropriate motor response occurs.

●After a motor response is achieved at 1 mA, reduce the stimulation intensity until the response disappears. Then turn the current up to the minimal current that results in a motor response. The goal is a minimal stimulation response between 0.2 and 0.5 mA. The presence of a motor response at <0.2 mA strongly suggests intraneural needle placement and the needle should be repositioned without injecting.

●After negative aspiration, inject 20 to 30 mL of LA containing epinephrine (as a vascular marker) in 5 mL increments, with gentle aspiration between injections.

●Stop injection and reposition the needle tip if the patient complains of pain or paresthesia, or if there is resistance to injection. Avoid high injection pressure. If using an injection pressure monitoring device, limit injection pressure to <15 pounds per square inch.

LOCAL ANESTHETIC CHOICE AND DOSE

Choice of local anesthetic — Local anesthetics (LAs) are chosen according to the goal of the block (surgical anesthesia or analgesia) and the desired duration of the effect of the block (table 1). If LA is used for other injections (eg, wound infiltration, periarticular infiltration), the total dose of LA should be calculated to avoid excessive dosing and minimize the risk of local anesthetic systemic toxicity (LAST). (See "Local anesthetic systemic toxicity".)

LAs for peripheral nerve blocks, including use of adjuvants, are discussed in more detail separately. (See "Overview of peripheral nerve blocks", section on 'Drugs'.)

Choices of LA for femoral nerve block (FNB) are as follows (table 1):

●Surgical anesthesia only – 2% lidocaine or 1.5% mepivacaine , which provide rapid onset, several hours of anesthesia, and limited postoperative analgesia (table 1).

For ultrasound guided block lower concentrations may provide adequate anesthesia. As examples:

•In dose finding studies of patients who had ultrasound guided femoral block for knee surgery, the minimum effective LA concentration in 90 percent of patients was 1% lidocaine [13] and 0.17% ropivacaine [14]. In both studies, 15 mL of LA was used for femoral block, and sciatic, obturator, and lateral femoral cutaneous blocks were performed as well.

•In a single institution retrospective study of patients who had single injection femoral nerve block for analgesia for anterior cruciate ligament repair, analgesia was similar after blocks using 0.5% bupivacaine versus 0.1 to 0.125% bupivacaine [15]. Motor block was not reported.

●Postoperative analgesia – 0.25% bupivacaine or 0.2 to 0.5% ropivacaine. We often mix 0.5% ropivacaine with an equal volume of saline to create a 0.25% solution, which is not commercially available. These lower concentrations may provide effective analgesia with a decreased risk of local anesthetic systemic toxicity.

●Surgical anesthesia and postoperative analgesia, either:

•For rapid onset – Equal volumes of a short-acting LA (2% lidocaine or 1.5% mepivacaine ) plus a long-acting LA (0.5% bupivacaine ).

Note that mixing LAs results in onset and duration that are both intermediate between the two agents [16].

•When rapid onset is not required – 0.5% bupivacaine or 0.5% ropivacaine.

Each of these agents should provide a duration of anesthesia between 7 to 8 hours and 9 to 14 hours of analgesia [3].

Volume of local anesthetic solution — LA volumes used for femoral nerve block vary. The author typically finds that no more than 20 mL of LA is required for ultrasound guided block. Higher volumes may be required for nerve stimulator guided block (up to 30 to 40 mL), particularly if a single injection is used, as the injection may occur farther from the nerve and separated by connective tissue. This was demonstrated by a randomized trial comparing ultrasound guided block with nerve stimulator guided block assessed by quadriceps contraction [10]. The volume of 0.5% ropivacaine required to provide effective sensory block in 95 percent of patients (ED95) was 22 mL with ultrasound guidance versus 41 mL with nerve stimulator guidance [10].

When determining the LA injection volume, the patient’s weight and the LA concentration should be calculated to remain within the maximum allowable dose, including any local anesthetic that might be injected by the surgeon (table 1). (See "Local anesthetic systemic toxicity", section on 'Local anesthetic dose'.)

CONTINUOUS FEMORAL NERVE BLOCK — A continuous femoral nerve block can be used to prolong analgesia beyond the duration of a single-shot block. For many knee procedures (eg, total knee arthroplasty), other more motor sparing blocks are commonly used. Continuous femoral block may be useful for lower extremity amputations, complex lower extremity surgical procedures where mobility limitations are deemed acceptable or a knee-immobilizing device is planned, and for patients where the risk of motor weakness is exceeded by the risk of prolonged and persistent opioid requirements.

Catheter placement technique — The technique for catheter placement is similar to the technique used for single-shot blocks, using ultrasound or nerve stimulator guidance as described above. The author uses ultrasound guidance, which allows visualization of the catheter placement and to verify local anesthetic spread around the nerve.

●We use a 19- or 20-gauge Tuohy needle for this technique. Standard Touhy needles and epidural catheters can be used; both through the needle and over the needle continuous block kits are available. Insulated, stimulating Touhy needles and catheters are also available. (See "Overview of peripheral nerve blocks", section on 'Equipment'.)

●For ultrasound guided continuous block in plane or out of plane needle placement can be used [17].

●Place the needle tip near the nerve, given the approach chosen. If nerve stimulation is used, place the needle tip such that nerve stimulation occurs at 0.2 to 0.5 mA. (See 'Nerve stimulation guided technique' above.)

When using ultrasound guidance, nerve stimulation can be used to confirm needle tip or catheter tip placement. Whether the use of a stimulating catheter is helpful or not during ultrasound guided block is unclear. In a randomized trial of 40 patients who underwent ultrasound guided block with nerve stimulation confirmation with the Touhy needle, use of a stimulating catheter did not improve block efficacy compared with no catheter stimulation, and prolonged block placement [18].

●After negative aspiration for blood, inject a small volume of saline or local anesthetic to distend the space into which the catheter will be threaded.

Note: Nerve stimulation guidance will no longer be possible after injecting saline or local anesthetic around the stimulating needle tip or catheter. Injecting 5 percent dextrose in water (D5W) may maintain or even augment twitch responses [19].

●Insert the catheter approximately 4 cm beyond the tip of the needle. If using ultrasound, visualize the catheter tip position near the nerve. Remove the needle without withdrawing the catheter.

●After negative aspiration, inject an epinephrine containing test dose (eg, 3 mL of 1.5% lidocaine with epinephrine [1:200,000]) to assess for intravascular injection. (See "Overview of peripheral nerve blocks", section on 'Adjuvants'.)

●After negative test dose, inject LA through the catheter as for single injection block.

Positioning, draping, and securing the catheter — Important technical aspects to consider when placing a catheter for continuous femoral nerve block (FNB):

●Placing a perineural catheter takes longer than a single injection block and sufficient time must be allocated if placement is planned prior to a surgical procedure. Catheter placement time may be decreased with the use of catheter over needle techniques.

●A large sterile field should be created to avoid contamination of the catheter. Either sterile towels or a clear plastic drape can be used but towels may be preferred as they are less apt to result in equipment sliding off the sterile field and subsequent contamination.

●In addition to sterile gloves, mask, and cap, we wear a sterile gown to avoid contamination of the catheter during placement. A sterile ultrasound sheath must be used to avoid contamination of the sterile field.

●More liberal local anesthetic (LA) is usually required at the needle insertion site, since a larger needle is used to facilitate catheter placement. In addition, immediately anesthetizing a track for catheter tunneling saves time later in the process. Slightly heavier sedation may also be necessary, though the patient should remain conscious enough to report a paresthesia or pain with injection through the needle or catheter.

●We tunnel the catheter away from the surgical site to decrease the rate of bacterial contamination, inadvertent dislodgement, and site leakage [20]. If the catheter is not tunneled it should be secured well.

●Chlorhexidine solution is typically used for skin decontamination prior to catheter insertion procedures. The use of a chlorhexidine impregnated patch at the catheter exit site has not been shown to decrease femoral nerve catheter colonization when used for infusions of two days or less [21].

Infusion drug dose — After injecting a bolus of LA as described above for single injection block, we start an infusion of LA at 5 to 12 mL/hour postoperatively, with a continuous or programmed intermittent bolus technique.

Specifics of our practice are as follows:

●For ambulatory patients with ambulatory catheters, we use a continuous infusion of 0.2% ropivacaine. Prior to discharge, the patient and their caregiver receive a comprehensive instruction sheet that includes the signs and symptoms of LA toxicity, pump maintenance information, and the acute pain service phone number for any issues that may arise.

●For inpatients, we generally use 0.2% ropivacaine delivered via an intermittent programmed bolus infusion strategy, which may improve analgesia and reduce opioid requirements compared with continuous infusion [22].

●Maximum safe local anesthetic delivery doses should take into account all sources of LA administration (other blocks, local anesthetic infiltration) and patient factors that increase the risk of toxicity (eg, older age, hepatic insufficiency). (See "Local anesthetic systemic toxicity", section on 'Risk factors for LAST'.)

SIDE EFFECTS AND COMPLICATIONS — Femoral nerve blocks (FNBs) are generally very safe. Complications common to all peripheral nerve blocks (ie, nerve injury, bleeding, local anesthetic [LA] systemic toxicity, infection) are discussed separately (see "Overview of peripheral nerve blocks", section on 'Complications'). Several complications are more likely with FNB than with many other peripheral nerve blocks.

Motor block — Femoral nerve block results in motor block of the hip flexor and knee extensor muscles, which can increase the risk of falls, limit patient participation in early physical therapy and delay discharge. The possibility of motor block limits the utility of femoral nerve block for ambulatory surgery. Whether the addition of a femoral nerve block increases the risk of patient falls in the postoperative period is unclear, and is discussed separately. (See "Anesthesia for total knee arthroplasty", section on 'Motor block and patient falls'.)

Patients who have had a femoral block should be considered at elevated risk for falls until the block resolves. This risk should be discussed with the patient and a knee immobilization device should be used if the patient attempts to ambulate while the block is in effect.

Infection — The risk of infection for a single injection femoral block is extremely low. The risk of infection is also low for continuous block catheters, but may be increased for femoral nerve block catheters compared with some other sites [23]. Increased risk of infection is also true for femoral venous catheters compared with other catheter insertion sites. This is discussed separately. (See "Central venous catheters: Overview of complications and prevention in adults", section on 'Infection control measures'.)

Of note, bacterial colonization is reported to occur for many continuous block catheters, without signs of infection. In one single institution study of over 200 continuous femoral nerve blocks with the catheter removed at 48 hours, the catheter was colonized in 57 percent of patients [24]. There were no signs of abscess, and patients were not treated with antibiotics. Three patients were thought to have transient bacteremia related to the catheter, which resolved after catheter removal.

When placing femoral nerve block catheters, we follow strict aseptic technique as described above, and monitor patients daily for signs of infection at the catheter site. If infection occurs we remove the catheter and continue to monitor daily. The risk of infection can be minimized by removing the catheter by 48 to 72 hours after placement. For patients who develop signs of infection, catheters are removed, and they are monitored closely.

The risk factors for infection are discussed separately. (See "Overview of peripheral nerve blocks", section on 'Infection'.)

Prolonged weakness/risk of reinjury — There may be increased risk of persistent weakness and delayed return to sport when a femoral nerve block is performed for anterior cruciate ligament (ACL) repair. However, the existing evidence is conflicting; some studies have found weakness that lasted up to six months after surgery [25,26], while others have found no difference between femoral nerve block and other forms of analgesia [27,28]. All of these studies involved single injection femoral nerve block.

In one randomized trial of patients who underwent ACL reconstruction with femoral nerve block versus adductor canal block (a motor sparing block), quadriceps strength was similar in the two groups at three and six months [28].

One single institution retrospective study of 360 patients who underwent ACL reconstruction found that femoral nerve block was associated with reduced isokinetic strength testing in the blocked leg at six months compared with the contralateral leg, and increased risk of ACL rupture during the first year after surgery (11.2 versus 5.7 percent) compared with patients who did not have femoral nerve block [29]. Conclusions from this study are limited by its retrospective nature and lack of information on the indication for femoral nerve block.

We discuss the potential risks of persistent weakness with patients and surgeon, and individualize the decision to use femoral nerve block, taking into account the risks and benefits of alternative options for analgesia. For some patients (eg, high level athletes), the risks of femoral nerve block, even though unclear, may outweigh analgesic benefits.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Local and regional anesthesia".)

SUMMARY AND RECOMMENDATIONS

●Anatomy

•The femoral nerve is derived from the ventral rami of L2-L4 spinal nerves. After dividing from the lumbar plexus the nerve travels into the leg, and lateral to the femoral artery at the level of the inguinal crease, where femoral nerve block is performed. (See 'Course of the nerve' above.)

•The femoral nerve provides sensory innervation to the skin of the anterior upper thigh, and through its saphenous branch, the medial lower leg (figure 3). It provides motor innervation to the muscles of the anterior thigh, including the quadriceps, and osseous innervation of portions of the pelvis, hip, anterior femur, patella, and medial proximal and distal tibia. (See 'Innervation' above.)

•The femoral nerve block is used for analgesia for injury or procedures of the hip, femur, knee, or medial lower leg. (See 'Clinical implications of anatomy' above.)

●Block technique – We use ultrasound guidance, with or without nerve stimulation. If ultrasound is not available, nerve stimulator guidance is a reasonable alternative. Block technique is briefly described here, and in more detail above.

Position the patient supine and flat to obtain access to the inguinal crease.

•Ultrasound guided block (See 'Ultrasound guided technique' above.)

-Place the ultrasound transducer at the inguinal crease (picture 4).

-Scan in the following sequence: Identify the femoral artery, then the iliopsoas muscle, fascia iliaca, fascia lata, femoral nerve (image 1).

-Position the needle tip beneath the fascia iliaca and lateral to the femoral nerve (movie 1).

-After negative aspiration, inject approximately 20 mL of local anesthetic (LA) in 5 mL increments, with gentle aspiration between injections, visualizing spread around the nerve (image 3).

•Nerve stimulator guided block (See 'Nerve stimulation guided technique' above.)

-Insert the needle 1 cm lateral to the femoral artery, slightly distal to the inguinal crease, and advance in a slightly cephalad direction watching for motor response in the thigh (picture 5).

-After appropriate quadriceps contraction (patellar twitch) (picture 6), and after negative aspiration, inject 30 mL of LA in 5 mL increments, with gentle aspiration between injections.

●Continuous block technique – Continuous block is performed as described for single injection block, using ultrasound or nerve stimulator guidance. (See 'Continuous femoral nerve block' above.)

●LA choice – The choice and concentration of LA is based on the goal for the block (ie, anesthesia versus analgesia), the desired duration of effect, other LA administered (eg, by the surgeon), and availability. (See 'Local anesthetic choice and dose' above and "Overview of peripheral nerve blocks", section on 'Drugs'.)

•For single injection block:

-For surgical anesthesia – 2% lidocaine or 1.5% mepivacaine.

-For postoperative analgesia – 0.25 to 0.5% bupivacaine or 0.2 to 0.5% ropivacaine

•For continuous block – Bolus injection as for single-injection block, followed by continuous infusion of 0.2% ropivacaine at 5 to 12 mL per hour with a continuous infusion or programmed intermittent bolus technique. (See 'Infusion drug dose' above.)

●Side effects and complications – Major adverse effects of femoral nerve block are very rare.

•Patients should be alerted to the possibility of motor block, which can cause quadriceps weakness and falls. (See 'Motor block' above.)

•The risk of infection may be higher with continuous femoral block than for some other continuous nerve blocks, particularly for catheters in place >48 hours. Patients should be monitored daily for infection. (See 'Infection' above.)

•The incidence of prolonged weakness after femoral nerve block for knee surgery is unclear. (See 'Prolonged weakness/risk of reinjury' above.)