Popliteal block procedure guide

INTRODUCTION — The popliteal block is a peripheral nerve block of the sciatic nerve at the level of the popliteal fossa. The sciatic nerve provides sensory and motor innervation of most of the lower leg. Thus, the popliteal block is used for anesthesia and analgesia for a wide variety of surgical procedures below the knee.

This topic will discuss the anatomy, ultrasound imaging, nerve stimulator guidance, and injection techniques for sciatic nerve block at the popliteal fossa. Proximal sciatic nerve block is discussed separately. (See "Sciatic blocks procedure guide".)

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" and "Ultrasound for peripheral nerve blocks".)

ANATOMY

Course of the sciatic nerve — The sciatic nerve is formed by the convergence of the ventral rami of spinal nerves L4 to S3 along the posterior ischium (figure 1). Each ventral ramus divides into dorsal and ventral branches, which translate into the lateral and medial aspects of the sciatic nerve, respectively. This lateral/medial arrangement of fibers within the sciatic nerve is maintained throughout its course, with the lateral fibers eventually becoming the common peroneal nerve (CPN) and the medial portion becoming the tibial nerve (TN) when the sciatic nerve divides in the distal thigh (figure 2) [1].

After travelling distally through the thigh, the sciatic nerve bifurcates into the tibial (medial) and common peroneal (lateral) nerves at approximately 6 to 10 cm proximal to the popliteal crease, though there is significant anatomic variation in the location of this split [2]. These nerves traverse the diamond-shaped popliteal fossa, (picture 1) which is bounded laterally by the biceps femoris tendon and medially by the semitendinosus and semimembranosus tendons.

The sciatic nerve is surrounded by a connective tissue sheath, referred to as the paraneural sheath, or paraneurium [3,4]. Beyond the bifurcation of the sciatic nerve, the paraneurium divides and the CPN and TN are surrounded by their own, separate paraneural sheaths (figure 3). The popliteal artery and vein travel outside this sheath.

Proximal to the popliteal crease, the popliteal vessels are deeper (more anterior) as they are continuations of the superficial femoral artery and vein after their passage through the adductor hiatus. At the level of the popliteal crease, the popliteal vessels are closely associated with the tibial nerve in an anteroposterior orientation, with the tibial nerve most superficial (posterior), popliteal vein just deep to it, and popliteal artery deepest (most anterior) (figure 4).

Innervation

Sensory

●Cutaneous – The sciatic nerve provides sensory innervation to the cutaneous skin of the leg and foot below the level of the knee, with the exception of a medial strip innervated by the saphenous nerve (figure 5).

•The CPN innervates the lateral skin of the calf (via the lateral sural cutaneous nerve), and the remaining skin of the calf and dorsum of the foot (via branches of the superficial peroneal nerve). The deep branch of the peroneal nerve innervates only the webspace between the first and second toes.

•Branches of the TN innervate the plantar surface of the foot.

●Bony innervation – The sciatic nerve innervates a distal portion of the posterior femur and all bones below the knee, with the exception of the medial tibial plateau and medial malleolus, which are innervated by branches of the femoral nerve.

Motor — After its division above the popliteal crease, the sciatic nerve continues as tibial and common peroneal nerves and innervates the muscles of the calf and foot.

●The CPN and its terminal branches innervate extensor muscles of the anterior compartment of the calf (ie, tibialis anterior, extensor hallucis longus and extensor digitorum longus). Their combined motor functions are eversion and dorsiflexion of the foot and ankle.

●The TN innervates muscles of the posterior compartment of the calf (ie, gastrocnemius, soleus, plantaris, flexor digitorum longus, flexor hallucis longus, tibialis posterior and popliteus), whose motor functions are inversion and plantar flexion of the foot.

CLINICAL ANATOMIC CORRELATIONS — For most indications either proximal sciatic or popliteal blocks can be used, as their block distributions do not vary in clinically relevant ways. However, since the popliteal block does not anesthetize muscles of the thigh, knee flexion is maintained after popliteal block.

For surgery on the medial lower leg, a saphenous nerve block may be required in addition to popliteal block (figure 6). Popliteal block without saphenous nerve block usually provides adequate analgesia for the patient to tolerate a calf tourniquet, since tourniquet pain is the result of pressure or ischemia of muscles, which are innervated by the sciatic nerve.

Multiple factors impact the clinical effects of sciatic nerve blockade. Many of these relate to the complex structure of the nerve and its surrounding tissue. As an example, clinical effects such as speed of onset, density of motor or sensory block and perhaps even block success may relate to whether injection is performed inside or outside the paraneural space.

As discussed above, there is significant variability in the location of the bifurcation of the sciatic nerve. Incomplete or failed block may occur if only one nerve is blocked with distal injection in a patient with an unexpectedly proximal bifurcation point. In our practice using ultrasound guidance, we aim to inject local anesthetic between the tibial and common peroneal nerves in their common sheath at the point of bifurcation (figure 7).

PATIENT POSITIONING — There are several options for patient positioning for popliteal block, chosen based on provider preference and patient factors:

●Supine, with the leg to be blocked elevated and slightly flexed at the knee, and with the calf and heel supported by a stand or other device that allows unobstructed access to the popliteal fossa (picture 2)

●Prone (picture 1)

●Lateral decubitus, with the leg to be blocked in the nondependent position and slightly flexed at the knee

SINGLE INJECTION BLOCK

Ultrasound guidance versus nerve stimulation — We use ultrasound guidance to perform popliteal blocks. When ultrasound is not available, nerve stimulation is a reasonable alternative. In general, ultrasound guidance improves block success, reduces placement and onset time, and is associated with decreased vascular puncture compared with nerve stimulation guidance for nerve blocks (see "Overview of peripheral nerve blocks", section on 'Ultrasound guidance'). In one randomized trial of 40 multiple injection posterior popliteal blocks, ultrasound guidance reduced the time needed to block and patients’ procedural pain, but block success rates were similar [5]. Another study comparing popliteal sciatic block with ultrasound versus nerve stimulation targeting any sciatic stimulation pattern showed better success with ultrasound (89.2 versus 60.6 percent) [6].

Nerve stimulation may be useful for nerve confirmation during ultrasound guided block, and can be invaluable if the nerve is not clearly visualized on ultrasound (eg, due to altered anatomy, obesity, edema).

Ultrasound guided block

Ultrasound imaging

●Select a high frequency 5 to 10 mHz, linear ultrasound transducer, using a general setting (set at neither the high nor low end of the frequency range). Set the depth on the ultrasound machine at approximately 3 to 5 cm.

●Place the transducer at the popliteal crease in a transverse orientation (picture 1).

●Identify the popliteal artery, and the vein just superficial to it.

●Identify the tibial nerve just superficial to the artery. Tilt the transducer slightly to identify the nerve as brightly as possible, due to significant anisotropy (picture 2).

●Slide the transducer proximally until the common peroneal nerve (CPN) is identified lateral and slightly superficial to the tibial nerve (TN) (figure 7).

●Continue to slide the transducer proximally to visualize the bifurcation of the sciatic nerve.

●The sciatic nerve appears as a round structure with a "honeycomb" appearance of hypoechoic nerve fascicle groups enmeshed in hyperechoic perineurium (image 1) [4,7,8]. It is best located between the lateral (short and long head of the biceps femoris) and medial (semimembranosus and semitendinosus) muscle groups.

●Move the transducer distally, tracing the nerve until a gap appears as it divides into the common peroneal nerve laterally and the tibial nerve medially (figure 7).

●The popliteal artery may be identified anterior (ventral) to the nerve, but is not intentionally sought due to its distance from the nerve.

Performing the block

●Infiltrate the skin and soft tissue at the injection site with 1% lidocaine, 1 to 3 mL, using a 25 gauge needle.

●With any patient position (supine, prone, or lateral decubitus), insert an echogenic B-bevel 20 to 22 gauge, 10 cm needle at the lateral edge of the transducer, using an in-plane approach, in a lateral to medial trajectory (picture 3). Take care to avoid inserting the needle into the tendon of the biceps femoris muscle.

●Target the block slightly distal to the sciatic nerve bifurcation, where both the common peroneal and tibial nerves are distinctly visible in a common sheath and slightly but not widely separated (figure 7 and image 2). Blockade at this location allows for placement of the needle tip between the tibial and common peroneal nerves, in the subparaneural space without passage through fascicles of either nerve. This approach results in shorter times for both motor and sensory blockade, greater longitudinal spread of local anesthetic (LA) along the nerve, and increased likelihood of success using a single needle pass [9]. In a randomized trial that compared popliteal blocks performed proximal versus distal to the sciatic bifurcation, distal block that targeted the CPN and TN individually resulted in faster onset of complete block (19.2 versus 26.1 minutes) [10]. In another trial including 50 patients who were randomly assigned to have ultrasound guided popliteal block performed 5 cm proximal to or 3 cm distal to the sciatic bifurcation, distal block resulted in shorter onset of sensory (21.4 versus 31.4 minutes) and motor block (21.5 versus 32.4 minutes) [11].

●Advance the needle through the biceps femoris muscle toward the nerves, entering the sub-paraneural space (figure 3 and movie 1). Subparaneural injection has been shown to increase block success (84 to 90 percent versus 56 to 63 percent) compared to an epineurial injection while maintaining a good safety profile [12].

●We use a single injection technique, though others use a three injection technique. The three injection technique may result in decreased time to block onset (12.5±7.9 minutes versus 15.8±7.9 minutes) compared with single injection with no difference in procedural discomfort or paresthesia [13]. Both techniques are described here.

•Single injection technique – Advance the needle ventral to the common peroneal nerve, and position the tip immediately lateral to the tibial nerve, between the two nerves. After negative aspiration, inject 1 to 2 mL saline, visualizing gentle separation of the nerves. After another negative aspiration, inject 10 to 30 mL LA in 5 mL increments, with gentle aspiration between injections. Visualize spread of LA around the nerves, moving the needle tip as necessary to achieve circumferential spread around and between the nerves.

•Three injection technique – Advance the needle ventral to the common peroneal nerve and position the tip immediately medial to the tibial nerve. After negative aspiration, inject 10 mL of LA in 5 mL increments, with gentle aspiration between injections. Withdraw the needle slightly to place the tip between the tibial and common peroneal nerves, and inject 10 mL LA incrementally as with the first injection. Finally, withdraw the needle, position the tip just lateral to the common peroneal nerve, and inject 10 mL of LA incrementally.

●If pain, paresthesia, or neural swelling (increase in the cross section of the nerve) occurs, stop the injection and redirect the needle tip away from the nerve.

Nerve stimulator guided block — Nerve stimulator guided popliteal block can be performed using a posterior or a lateral needle insertion site; the authors use a lateral approach. An advantage of the lateral approach is that it is performed with the patient supine, which simplifies positioning and avoids having to reposition the patient after the block for most procedures.

We describe single injection techniques here, preferentially targeting the tibial nerve, which is more medial than the common peroneal nerve, with a large (30 mL) single-injection of local anesthetic. Two-injection techniques have also been described for popliteal blocks [14,15]. For a two-injection block, the common peroneal and tibial nerves are identified separately, and typically half of the local anesthetic (15 mL) is injected at each nerve. Single injection approaches are as successful as two injection popliteal sciatic blockade, but single injection at the tibial nerve demonstrates a faster onset of action [16].

Nerve stimulation equipment — The authors set the nerve stimulator to a pulse width of 100 ms at 1 to 2 Hz and an initial current of 1.0 mA. We use a shielded, B-bevel, 20 to 22 gauge 10 cm stimulating needle. Connect the stimulator to the needle and to an electrode on the patient’s skin. (See "Overview of peripheral nerve blocks", section on 'Equipment for nerve stimulator guidance'.)

Nerve stimulation patterns — Two patterns of evoked response may occur during nerve stimulator guided popliteal block.

●Tibial nerve stimulation – Inversion and plantar flexion of the foot

●Common peroneal stimulation – Eversion and dorsiflexion of the foot

"TIP" (tibial = inversion, plantarflexion) and "PED" (peroneal = eversion, dorsiflexion) are useful mnemonics for these stimulation patterns. The preferred motor response is foot inversion/plantar flexion, evidence of tibial nerve stimulation [17,18].

Once stimulation occurs at 1 mA, decrease the stimulus current until the motor response disappears, then turn back up to the minimal current that results in a 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.

Posterior (prone) approach — The posterior approach to nerve stimulator guided block is often referred to as the classical approach; the needle is inserted in the posterior thigh in the popliteal fossa [19-21]. The intertendinous approach is a variant of the classical approach, using a more proximal needle insertion site [22,23]. In a randomized trial including approximately 100 nerve stimulator guided single injection popliteal blocks, the intertendinous approach resulted in faster block onset, and increased block success if tibial nerve stimulation was obtained [18].

●Position the patient prone, with the foot in position to allow for free, unrestricted motion so as to easily detect elicited stimulation. We place a roll under the shin to facilitate this.

●Identify the borders of the popliteal fossa, which create a triangle: the popliteal crease distally, the biceps femoris tendon laterally, and the semitendinosus tendon medially. Ask the patient to flex the knee against resistance to more easily palpate the medial and lateral borders.

●Draw a line from the apex of the popliteal triangle, bisecting the base.

•For the classical approach, used by the authors, mark a needle insertion point 7 cm proximal to the popliteal crease, and one cm lateral to the line bisecting the popliteal triangle (figure 8).

•For the intertendinous approach, mark a needle insertion point 10 to 12 cm proximal to the popliteal crease, on the line bisecting the popliteal triangle.

●Infiltrate the skin and soft tissue at the injection site with 1% lidocaine, 1 to 3 mL, using a 25 gauge needle.

●Insert the needle at a 45 degree angle cephalad. Set the stimulator current to 1 to 1.2 mA. Advance the needle until a motor response occurs in the calf, ankle, or foot. For the classical approach, nerve depth is often 1.5 to 2 cm from the skin, whereas the nerve is typically deeper at more proximal insertion sites (eg, 3 to 4 cm at 10 cm from the popliteal crease) [24].

●Aim for tibial nerve stimulation and manage the stimulator current as described above (see 'Nerve stimulation patterns' above). If common peroneal stimulation occurs, withdraw the needle slightly and redirect slightly medially, seeking tibial nerve stimulation. If no stimulation occurs, reassess landmarks and confirm proper stimulator function and connections.

●After negative aspiration, inject 35 to 45 mL of local anesthetic containing epinephrine (as a vascular marker), in 5 mL increments, with gentle aspiration between injections. Stop injection and reposition the needle tip if blood appears in the syringe, the patient complains of pain or paresthesia, or if there is resistance to injection. If paresthesia is elicited, withdraw the needle 1 to 2 mm.

Lateral (supine) approach

●Position the patient supine, with the leg extended straight and the foot in position to allow for unrestricted motion so as to easily detect elicited stimulation (eg, hanging freely off the bed or propped slightly on a roll).

●Sit on a stool beside the bed on the side to be blocked, with the bed height adjusted so the patient’s leg is just below the clinician’s eye level.

●Palpate the groove between the vastus lateralis and biceps femoris. Mark the needle insertion site in this groove, 7 cm cephalad to the lateral condyle of the femur (picture 4).

●Infiltrate the skin and soft tissue at the injection site with 1% lidocaine, 1 to 3 mL, using a 25 gauge needle.

●Using the non-dominant hand to stabilize the tissue between two fingers, insert the block needle at the marked site and advance to contact the femur, which confirms appropriate initial insertion site.

●Withdraw the needle to the skin and redirect 30 degrees posteriorly (towards the bed).

●Set the stimulator current to 1 to 1.2 mA. Advance the needle, seeking tibial nerve stimulation and managing the stimulator current as described above. (See 'Posterior (prone) approach' above and 'Nerve stimulation patterns' above.)

●If common peroneal stimulation occurs, withdraw the needle slightly and redirect slightly ventrally (anterior) seeking tibial nerve stimulation. If no stimulation occurs, reassess landmarks and confirm proper stimulator function and connections.

●After negative aspiration, inject 35 to 45 mL of local anesthetic containing epinephrine (as a vascular marker), in 5 mL increments, with gentle aspiration between injections. Stop injection and reposition the needle tip if blood appears in the syringe, the patient complains of pain or paresthesia, or if there is resistance to injection. If paresthesia is elicited, withdraw the needle 1 to 2 mm.

LOCAL ANESTHETIC CHOICE AND DOSE — 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). LAs for peripheral nerve blocks and the use of adjuvant drugs are discussed in more detail separately. (See "Overview of peripheral nerve blocks", section on 'Drugs'.)

●Choice of LA – Usual options for popliteal block are as follows:

•Surgical anesthesia only – 2% lidocaine or 1.5% mepivacaine.

•Postoperative analgesia – 0.25 to 0.5% bupivacaine or 0.5% ropivacaine.

•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 or 1% ropivacaine). Note that mixing LAs results in onset and duration that are both intermediate between the two agents [25].

-When rapid onset is not required (ie, 30 minutes for onset is acceptable) – 0.25 to 0.5% bupivacaine or 0.5% ropivacaine.

●Volume of LA – Local anesthetic volumes used for popliteal nerve blocks vary widely.

•Ultrasound guided block – A reasonable block volume for ultrasound guided popliteal block may be between 10 and 30 mL, depending on factors such as block intent (surgical anesthesia versus postoperative analgesia), proximity of injection to the nerve, intended duration of blockade, and maximum safe dose. In an up and down dose finding study for 0.5% ropivacaine in 32 patients who underwent ultrasound guided popliteal block, the minimum effective dose for 95 percent of patients (ED95) was 16 mL [26].

•Nerve stimulator guided block – Higher local anesthetic volumes of 35 to 45 mL may be required for successful nerve stimulator guided block, since injection may occur further from the target nerve, and potentially separated from the nerve by connective tissue barriers. In a dose finding study in patients who underwent nerve stimulator guided sciatic nerve block, the effective dose required to produce sensory and motor block in 95 percent of subjects (ED95) was 30 mL for popliteal block [27].

If multiple procedures are planned (eg, additional femoral block, or local infiltration), the total dose of LA should be calculated to avoid excessive dosing and to minimize the risk of local anesthetic systemic toxicity (LAST) (table 1). (See "Local anesthetic systemic toxicity".)

CONTINUOUS POPLITEAL BLOCK — Continuous block catheters may be used to provide prolonged postoperative analgesia, beyond the duration provided by a single injection block.

●Catheter placement technique – The technique for placing the catheter is similar to the technique used for single injection block.

•Use a 19 or 20 gauge Tuohy needle for this technique. Insulated, stimulating Touhy needles are available.

•After anesthetizing the skin and soft tissue, advance the Tuohy needle toward the nerve.

•Place the needle tip and catheter near the nerve, given the approach chosen.

-If ultrasound guidance is used, position the needle either between the tibial and common peroneal nerves or beneath the paraneural sheath if one can be identified.

-If nerve stimulation is used, place the needle tip such that tibial nerve stimulation occurs at 0.2 to 0.5 mA. (See 'Nerve stimulation patterns' above.)

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

•While stabilizing the needle, insert a catheter through the needle and advance far enough to allow the catheter perforations to bathe the nerve, typically 4 to 6 cm beyond the tip of the needle. The optimal distance for catheter insertion has not been well studied.

•If using ultrasound, carefully visualize catheter insertion to identify and correct catheter passage away from the nerve.

•Remove the needle without withdrawing the catheter.

•After negative aspiration, inject 15 to 30 mL of LA through the catheter. If using ultrasound, visualize gentle displacement of the nerve during injection.

●Positioning, draping and securing the catheter – Important technical aspects to consider when placing a catheter for continuous block include:

•Placing a perineural catheter takes longer than a single injection block and sufficient time must be allocated prior to surgery (budget 15 to 30 minutes).

•Create a large sterile field to avoid catheter contamination. Sterile towels and/or a clear plastic drape can be used.

•Wear a mask, cap, and sterile gloves during catheter placement. Use a sterile ultrasound sheath to avoid contamination of the surgical field.

•Secure the catheter well to prevent leakage and/or dislodgement.

-We apply surgical glue at the catheter insertion site, primarily to prevent leakage, which can disrupt dressing integrity and lead to catheter dislodgement. The glue also helps fix the catheter in place.

-We apply liquid adhesive (eg, tincture of benzoin or similar) around the insertion site.

-We use a catheter fixation device. Avoid placing such devices within the surgical field or where a tourniquet will be placed.

•Coil the excess catheter and fix it to the skin with a transparent adhesive dressing. Ensure the insertion site, fixating device, and catheter are well covered and visible.

●Infusion drug dose — After injecting a bolus of LA as described above, we start an infusion of 0.125% bupivacaine or 0.2% ropivacaine at 5 to 8 mL/hour postoperatively, with a continuous infusion and a patient controlled bolus of 5 mL per 30 minutes. Ambulatory catheters, which can be managed and removed at home by the patient, are well-described and have an excellent safety record [28]. Ambulatory patients receive comprehensive instructions on the signs and symptoms of LA toxicity and pump maintenance, and the acute pain service phone number prior to discharge.

SIDE EFFECTS AND COMPLICATIONS — Major complications of popliteal block are very rare. Complications common to all peripheral nerve blocks (eg, nerve injury, bleeding, local anesthetic systemic toxicity [LAST], infection) are discussed in detail separately (see "Overview of peripheral nerve blocks", section on 'Complications'). Several complications are of particular concern with popliteal block.

●Motor block – Motor weakness associated with popliteal block and other lower extremity blocks can cause patient falls and poor rehabilitation after surgery. The most important motor deficit associated with popliteal block is the inability to dorsiflex the ankle (ie, foot drop), which causes the foot to drag and catch on the ground. The resulting falls can lead to significant morbidity and mortality. (See "Falls in older persons: Risk factors and patient evaluation", section on 'Morbidity and mortality'.)

Motor block may be reduced but not eliminated by using dilute local anesthetic solutions and possibly by using ropivacaine rather than bupivacaine [29]. Patients and families should be alerted to the risk of motor block after popliteal block, particularly in ambulatory settings.

●Infection – Infection is rare after both single injection and continuous popliteal nerve block. In a prospective observational study of 400 continuous popliteal blocks left in place for a median of two days, there was one infection, which was a thigh abscess in a patient with a sutured catheter in place for five days [30]. In a larger prospective study of 1000 surgical patients who had perineural popliteal catheters in place for a median of 48 hours (range 30 to 190 hours), there were no cases of infection [31].

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 sciatic nerve is derived from spinal nerves L4-S3 (figure 1). It exits the pelvis and travels through the posterior thigh, ultimately traversing the popliteal fossa, where it divides into the tibial and common peroneal nerves.

•The popliteal block is a peripheral nerve block performed at the level of the sciatic nerve bifurcation.

•Popliteal blocks are used for surgery of the lower leg, ankle, and foot (figure 5). (See 'Anatomy' above.)

●Single injection block technique – We use ultrasound guidance, with or without nerve stimulator confirmation of the nerves. If ultrasound is unavailable, nerve stimulator guided block is a reasonable option. Technique is described briefly here and in more detail above. (See 'Ultrasound guidance versus nerve stimulation' above.)

Position the patient supine, prone, or in the lateral decubitus position, depending on provider preference and patient factors (picture 1 and picture 2). (See 'Patient positioning' above.)

•Ultrasound guided block – We perform ultrasound guided block as follows, with further explanation above (movie 1). (See 'Ultrasound guided block' above.)

-Use a high frequency (eg, 5 to 10 mHz) linear ultrasound transducer with the depth set to 3 to 5 cm.

-Place the transducer in the popliteal fossa, 5 to 8 cm proximal to the popliteal crease, transverse to the femur (picture 1).

-Identify the bifurcation of the sciatic nerve into the tibial and common peroneal nerves (figure 7 and image 2).

-Insert the block needle in-plane, positioning the tip immediately lateral to the tibial nerve.

-After negative aspiration, inject 10 to 30 mL of local anesthetic in 5 mL increments, with gentle aspiration between injections.

•Nerve stimulator guided block – Nerve stimulation can be used on its own, or for nerve confirmation during ultrasound guidance. Tibial nerve stimulation causes inversion and plantar flexion of the foot ("TIP"), whereas common peroneal nerve stimulation causes eversion and dorsiflexion ("PED"). (See 'Nerve stimulator guided block' above and 'Nerve stimulation patterns' above.)

-For a posterior approach, insert the needle 7 cm proximal to the popliteal crease, and 1 cm lateral to the midline (figure 8).

-For a lateral approach, insert the needle 7 cm cephalad to the lateral condyle of the femur, in the groove between the vastus lateralis and biceps femoris (picture 4).

-For either approach, aim for tibial nerve stimulation.

-After appropriate motor response and after negative aspiration, inject 35 to 45 mL of local anesthetic containing epinephrine (as a vascular marker), in 5 mL increments, with gentle aspiration between injections.

●Continuous block technique – Continuous popliteal block is performed as described for single injection block, using a Touhy needle with a 19 or 20 gauge catheter inserted through it and 4 to 6 cm beyond the needle tip. (See 'Continuous popliteal block' above.)

●Local anesthetic choice (see 'Local anesthetic choice and dose' above)

•For single injection block:

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

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

•For continuous block: Bolus injection as for single injection block, followed by continuous infusion of 0.125% bupivacaine or 0.2% ropivacaine at 5 to 8 mL per hour.

●Side effects and complications – Major side effects of popliteal block are very rare. Patients should be alerted to the possibility of motor block. (See 'Side effects and complications' above.)