Popliteal Block: Lateral Approach
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The lateral approach to popliteal blockade is a block of the sciatic nerve at the level of the popliteal fossa. This is an intermediate nerve block technique and sound knowledge of the principles of nerve sti-mulation and anatomic characteristics of the sciatic nerve are needed for its successful implementation. This block is well-suited for surgery on the calf, Achilles tendon, ankle, and foot. It provides complete analgesia for the calf tourniquet without the need for supplementary blocks of the saphenous nerve. |
The sciatic nerve consists of two separate nerve trunks, the tibial and common peroneal nerves. A common epineural sheath envelops these two nerves at their outset in the pelvis. As the sciatic nerve descends toward the knee, the two components eventually diverge in the popliteal fossa, giving rise to the tibial and common peroneal nerves. This division of the sciatic nerve usually occurs between 50 and 120 mm proximal to the popliteal fossa crease. |
An MRI image of the popliteal fossa at the level of the blockade (8 cm above the popliteal fossa crease). Note the position of the sciatic nerve between the biceps and semitendinosus muscles. During block performance, stimulation of the common peroneal nerve is usually obtained first (65%) because this nerve is positioned lateral and more superficial than the tibial nerve. |
Popliteal block results in anesthesia of the entire distal two thirds of the lower extremity, with the exception of the medial aspect of the leg. Cutaneous innervation of the medial leg below the knee is provided by the saphenous nerve. The saphenous nerve is a cutaneous extension of the femoral nerve. Depending on the level of surgery, the addition of a saphenous nerve block may be required for complete surgical anesthesia. |
The patient is in the lateral position. The foot on the side to be blocked should be positioned so that even the slightest movements of the foot or toes can be easily observed. This is best achieved by placing the foot on a foot rest. Attention should be paid so that the Achilles tendon is also protruding off the foot rest. This positioning allows easy visualization of any foot movement during nerve stimulation. |
A standard regional anesthesia tray is prepared with the following equipment:
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Surface Landmarks
The following surface anatomy landmarks are used to determine the insertion point for the needle:
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Anatomic Landmarks
Landmarks for the lateral approach to popliteal block include:
The needle insertion site is marked in the groove between the vastus lateralis and biceps femoris muscle. Note that the lateral femoral epycondyle is another landmark that can be used in this technique. It is easily palpated on the lateral aspect of the knee. This landmark is positioned 1 cm cephalad to the popliteal fossa crease. TIP: In some patients, the biceps muscle may be atrophic and the iliotibial aponeurosis may be more prominent. In such cases, the needle insertion site is labeled in the groove between the vastus lateralis and the iliotibial tract. |
Maneuvers to accentuate the anatomic landmarks
When not immediately apparent visually, the groove between the vastus lateralis and biceps femoris is examined by firmly pressing the fingers of the palpating hand against the adipose tissue in the groove approximately at 8 cm above the popliteal fossa crease. TIPS:
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The operator should be seated, facing the side to be blocked. The height of the bed with the patient is adjusted to allow for an ergonomic position and a greater precision during block placement. This position also allows the performer to simultaneously monitor both the patient and the responses to nerve stimulation. The figure below depicts the correct patient and anesthesiologist position during block placement. |
Local anesthetic skin infiltration
The site of needle insertion is cleaned with an antiseptic solution and infiltrated with local anesthetic at the site of estimated needle insertion using a 1½" 25 gauge needle. It is useful to infiltrate the skin in a line, rather than raise a single skin wheel. This allows for a needle reinsertion at a different site when necessary, without a need to anesthetize the skin again. |
Needle insertion
A 10cm 22G needle is connected to a nerve stimulator, inserted in a horizontal plane between the vastus lateralis and biceps femoris muscles and advanced to contact the femur. The contact with the femur is important because it provides information on the depth of the nerve (typically 1-2 cm beyond the skin-femur distance) as well as on the angle that the needle will need to be redirected posterior in order to stimulate the nerve. The initial current intensity is initially set at 1.5 mA. |
Keeping the fingers of the palpating hands firmly pressed and immobile in the groove, the needle is then withdrawn to the skin, redirected 30º posterior to the angle at which the femur was contacted and advanced toward the nerve. |
This MRI image demonstrates:
When the sciatic nerve is not localized on the first needle pass, the needle is withdrawn to the skin level and the following algorithm is followed:
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The ultimate goal of nerve stimulation is to obtain visible or palpable twitches of the foot or toes at a current of 0.2-0.5 mA.
- Stimulation of the sciatic nerve can result in tibial (plantar flexion) or common peroneal (dorsiflexion) response. Either of these is acceptable when a low-intensity current stimulation is obtained and large volume of local anesthetic is used. injection of large volume of local anesthetic will spread within the sheath to block both divisions of the nerve.
- Some authors recommend a double-stimulation/injection technique to increase the success rate of blockade of both division of the nerve. This involves, succinctly stimulating and injection both divisions of the sciatic nerve (tibial and common peroneal). This is not necessary with the technique described in this book.
- Isolated twitches of the calf muscles should not be accepted because they may be the result of stimulation of the sciatic nerve branches to the calf muscles that may be outside the sciatic nerve sheath.
- In some patients with long standing diabetes mellitus, renal failure or peripheral neuropathy, it may not be possible to obtain stimulation with low current intensity. In this case, stimulation of the tibial nerve (plantar flexion) often proves to be more reliable.
After the initial stimulation of the sciatic nerve is obtained, the stimulating current is gradually decreased until twitches are still seen or felt at 0.2-0.5 mA. This typically occurs at a depth of 5-7 cm. At this point, the needle should be stabilized and after negative aspiration for blood, 35-45 mL of local anesthetic is slowly injected. The hands should be kept as immobile as possible to prevent injection outside the sheath of the sciatic nerve. |
Troubleshooting
| Response Obtained | Interpretation | Problem | Action |
| Local twitch of the biceps muscle | Direct stimulation of the biceps femoris muscle | Too shallow a placement of the needle | Advance the needle deeper |
| Local twitch of the vastus lateralis muscle | Direct stimulation of the vastus lateralis muscles | Too anterior a placement of the needle | Withdraw the needle and reinsert posteriorly |
| Twitch of the calf muscles without the foot or toe movement | Stimulation of the muscular branches of the sciatic nerve | These small branches are often outside the sciatic sheath | Disregard and continue advancing the needle until foot/toes twitches are obtained |
| Vascular puncture | Blood in the syringe mostly commonly indicates placement into the popliteal artery or vein | Too deep and anterior a placement of the needle | Withdraw and redirect laterally |
| Twitches of the foot or toes | Stimulation of the sciatic nerve | None | Accept and inject local anesthetic |
Popliteal block requires larger volume of local anesthetic in order to achieve anesthesia of both divisions of the nerve. The choice of the type and concentration of local anesthetic should be based on whether the block is planned for surgical anesthesia or pain management. As could be seen in the table below, type and concentration of local anesthetics as well as the choice of additives to local anesthetic influence the onset and particularly duration of the blockade.
| Onset (min) |
Anesthesia (hrs) | Analgesia (hrs) | |
| 3% 2-Chloroprocaine (+ HCO3) | 10-15 | 1 | 2 |
| 3% 2-Chloroprocaine (+HCO3 + epinephrine) | 10-15 | 1.5-2 | 2-3 |
| 1.5% Mepivacaine (+ HCO3) | 15-20 | 2-3 | 3-5 |
| 1.5% Mepivacaine (+ HCO3 + epinephrine) | 15-20 | 2-2 | 3-8 |
| 2% Lidocaine (+ HCO3 + epinephrine) | 10-20 | 2-5 | 3-8 |
| 0.5% Ropivacaine | 15-30 | 4-8 | 5-12 |
| 0.75% Ropivacaine | 10-15 | 5-10 | 6-24 |
| 0.5 Bupivacaine (or l-bupivacaine) | 15-30 | 5-15 | 6-30 |
This technique is associated with a moderate patient discomfort because the needle transverses the biceps femoris muscle and adequate sedation and analgesia are necessary. Administration of midazolam (2-4 mg IV) and a short-acting narcotic (250-750 µg alfentanyl) assures patient comfort and prevents patient movement during block performance. Failure to administer appro-priate premedication makes it difficult to interpret response to nerve stimulation due to patient's moving during needle advancement. A typical onset time for this block is 10-25 minutes, depending on the type, concentration and volume of local anesthetic used. The first signs of onset of blockade are usually report by the patient that the foot "feels different" or inability to wiggle toes. Sensory anesthesia of the skin with this block is often the last to develop. Inadequate skin anesthesia despite the apparent timely onset of the blockade is common and it may take up to 30 minutes to develop. Thus, local infiltration at the site of the incision by the surgeon is often all that is needed to allow the surgery to proceed.
| Infection | Use a strict aseptic technique |
| Hematoma |
- Avoid multiple needle passes with a continuous block needle; the larger needle
diameter and/or Tuohy design may result in a hematoma of the biceps femoris or
vastus lateralis muscles - When the nerve is not localized on the first two or three needle passes, localize the nerve using a smaller gauge, single-shot needle first and then reinsert the continuous needle using the same angle; this technique is essentially similar to the localization of the internal jugular vein with a "localization needle" before inserting a large needle for canalization |
| Vascular puncture |
- Avoid too deep an insertion of the needle, because the vascular sheath is
positioned medially and deeper to the sciatic nerve - When the nerve is not localized within 2 cm after the local twitches of the biceps muscle cease, the needle should be withdrawn and reinserted at a different angle, rather than advanced deeper |
| Nerve injury |
- Exceedingly rare; use nerve stimulation and slow needle advancement; do not inject
when the patient complains of pain or high pressures on injection are met; do not
inject when stimulation is obtained at <0.2 mA current (100µsec) - Avoid a combination of epinephrine in local anesthetic and application of a tourniquet over the injection site to decrease the risk of prolonged ischemia of the nerve |
| Pressure necrosis of the heel |
- Instruct the patient on the care of the insensate extremity - Use heel padding and frequent repositioning |
- Benzon HT, Kim C, Benzon HP, et al: Correlation between evoked motor response of the sciatic nerve and sensory blockade. Anesthesiology 1997; 87:548-52
- Hadzic A, Vloka JD: A comparison of the posterior versus lateral approaches to the block of the sciatic nerve in the popliteal fossa. Anesthesiology 1998; 88:1480-6
- Hadzic A, Vloka JD, Singson R, Santos AC, Thys DM: A comparison of intertendinous and classical approaches to popliteal nerve block using magnetic resonance imaging simulation. Anesth Analg 2002; 94:1321-4
- McLeod DH, Wong DH, Claridge RJ, Merrick PM: Lateral popliteal sciatic nerve block compared with subcutaneous infiltration for analgesia following foot surgery. Can J Anaesth 1994; 41:673-6
- McLeod DH, Wong DH, Vaghadia H, Claridge RJ, Merrick PM: Lateral popliteal sciatic nerve block compared with ankle block for analgesia following foot surgery. Can J Anaesth 1995; 42:765-9
- Sunderland S: The sciatic nerve and its tibial and common peroneal divisions. Anatomical features. Nerves and Nerve Injuries. Edinburgh and London, E. & S. Livingstone LTD, 1968, pp 1012-95
- Vloka JD, Hadzic A, Kitain E, Lesser JB, Kuroda M, April EW, Thys DM: Anatomic considerations for sciatic nerve block in the popliteal fossa through the lateral approach. Reg Anesth 1996; 21:414-8.
- Vloka JD, Hadzic A, Lesser JB, Kitain E, Geatz H, April EW, Thys DM: A Common Epineural Sheath for the Nerves in the Popliteal Fossa and Its Possible Implications for Sciatic Nerve Block. Anesth Analg 1997; 84:387-90
- Vloka JD, Hadzic A, April EW, Geatz H, Thys, DM: Division of the sciatic nerve in the popliteal fossa and its possible implications in the popliteal nerve blockade. Anesth Analg 2001; 92:215-7
- Zetlaoui PJ, Bouaziz H: Lateral approach to the sciatic nerve in the popliteal fossa. Anesth Analg 1998; 87:79-82
