16 Popliteal and Saphenous Block

Perspective

The nerves blocked in the popliteal fossa—the tibial and peroneal nerves—are extensions of the sciatic nerve. The principal use of this block is for foot and ankle surgery. The addition of a saphenous nerve block improves comfort for many patients undergoing the popliteal block because medial lower leg and ankle sensory blockade makes tourniquets and medial ankle surgery more comfortable.

Patient Selection

To use the classic form of this block, the patient must be able to assume the prone position. Elicitation of a paresthesia or motor response is desirable but not essential; however, block effectiveness decreases without these end points.

Pharmacologic Choice

The principal use of these blocks is to provide sensory analgesia; thus, lower concentrations of a local anesthetic are practical, in contrast to situations in which motor blockade is essential. Concentrations of 1% lidocaine, 1% mepivacaine, 0.25% to 0.5% bupivacaine, and 0.2% to 0.5% ropivacaine are effective.

Traditional Block Technique

As illustrated in Figure 16-1, the cephalad popliteal fossa is defined by the semimembranosus and semitendinosus muscles medially and the biceps femoris muscle laterally. Its caudad extent is defined by the gastrocnemius muscles both medially and laterally. If this quadrilateral area is bisected, as shown in Figure 16-1, the area of interest to the anesthesiologist is the cephalolateral quadrant (hatched area). Here, both tibial and common peroneal nerve block is possible. The tibial nerve is the larger of these two nerves; it separates from the common peroneal nerve at the upper limit of the popliteal fossa and sometimes higher. The tibial nerve continues the straight course of the sciatic nerve and runs lengthwise through the popliteal fossa immediately under the popliteal fascia. Inferiorly, it passes between the heads of the gastrocnemius muscles. The common peroneal nerve follows the tendon of the biceps femoris muscle along the cephalolateral margin of the popliteal fossa, as illustrated in Figure 16-2. After the common peroneal nerve leaves the popliteal fossa, it travels around the head of the fibula and divides into the superficial peroneal and deep peroneal nerves.