SAPHENOUS NERVE BLOCK AT A GLANCE
Indications: saphenous vein stripping or harvesting; supplementation for medial foot/ankle surgery in combination with a sciatic nerve block, and analgesia for knee surgery in combination with multimodal analgesia.
Transducer position: transverse on anteromedial thigh at the junction between the middle and distal third of the thigh or below the knee at the level of the tibial tuberosity, depending on the approach chosen (proximal or distal) (Figure 33E–1)
Goal: local anesthetic spread lateral to the femoral artery and deep to the sartorius muscle or more distal, below the knee, adjacent to the saphenous vein.
Local anesthetic: 5–10 mL
Transducer position and needle insertion to block the saphenous nerve (A) at the level of the lower third of the thigh and (B) below the knee.
The saphenous nerve is a terminal sensory branch of the femoral nerve. It supplies innervation to the medial aspect of the leg down to the ankle and foot. It also sends infrapatellar branches to the knee joint. A saphenous nerve block is useful as a supplement to sciatic block for foot and ankle procedures that involve the medial aspect of the malleolus and the foot. The block has also been reported as a supplement to multimodal analgesia protocols in patients having knee arthroplasty. Typically, a more proximal (mid-thigh) approach and a larger volume of local anesthetic is used for this “adductor canal block”. Several approaches have been described to block the saphenous nerve along its route from the inguinal area to the medial malleolus (Figure 33E–2). The use of ultrasound (US) guidance has improved the success rates of the saphenous blocks compared with field blocks below the knee and blind transsartorial approaches.
Various approaches to the saphenous nerve block: the perifemoral typically targets the nerve to the vastus medialis muscle with nerve stimulation; the subsartorial at the femoral riangle; subsartorial at the adductor canal; at the medial femoral condyle, between the tendons of the sartorius and the gracilis muscle; once the femoral vessels have crossed the adductor hiatus to become the popliteal vessels; the paravenous approach using the saphenous vein as a landmark at the level of the tibial tuberosity; and at the level of the medial malleolus.1
The sartorius muscle descends in a lateral to medial direction across the anterior thigh and forms a “roof” over the adductor canal in the lower half of the thigh. The muscle appears as a trapezoid shape beneath the subcutaneous layer of adipose tissue. The sides of the triangular canal are formed by ...