Saphenous nerve blockade is useful as a diagnostic, prognostic, or therapeutic procedure in painful disorders involving the knee, ankle, and foot.
After informed consent is obtained, the patient is placed in the supine or lateral position. The saphenous nerve is located at the medial surface of the medial condyle of the femur at about the same level as the apex of the patella. The patient is prepared in a standard aseptic fashion over an area large enough to allow palpation of landmarks, and sterile technique is used throughout the procedure. A 1½-in. (4-cm), 25-gauge needle is inserted perpendicular to the skin just below the medial surface of the tibial condyle. After negative aspiration, 5 to 10 mL of local anesthetic is injected subcutaneously to block the saphenous nerve (Fig. 67-18).
FIGURE 67-18. Saphenous nerve block at the knee. Approach for saphenous injection and neural blockade at the knee.
The saphenous nerve is the terminal branch of the femoral nerve. It provides cutaneous innervation to the skin overlying the medial, anteromedial, and posteromedial aspects of the leg from just above the knee to the level of the medial malleolus and, in some patients, to the medial aspect at the base of the great toe. There is no motor component.
The saphenous vein may accompany the saphenous nerve, and the patient should be made aware of the possibility of a hematoma from venous puncture. Other complications from the saphenous nerve block are rare, especially when care is taken to avoid an intraneural injection. Severe pain on injection suggests the possibility of an intraneural injection, and the needle should be repositioned immediately.