Ultrasound-guided saphenous nerve block is utilized as a diagnostic and therapeutic maneuver in the evaluation and treatment of distal lower extremity pain thought to be mediated via the saphenous nerve. The most common pain syndrome mediated via the saphenous nerve is a postoperative neuropathy secondary to surgical injuries to the saphenous nerve during vein harvesting procedures for coronary artery bypass surgery or during lower extremity vein stripping procedures. Less commonly, saphenous neuralgia can occur as an isolated mononeuropathy without apparent cause. The symptoms associated with saphenous neuralgia depend on the point at which the nerve is damaged (Fig. 148.1).

Ultrasound-guided saphenous nerve block can also be utilized to provide surgical anesthesia when combined with ultrasound-guided sciatic nerve block for distal lower extremity surgery including distal amputations, debridements, skin grafting procedures, and fracture reductions and fixations. Ultrasound-guided saphenous nerve block with local anesthetics can be employed as a diagnostic maneuver when performing differential neural blockade on an anatomic basis to determine if the patient’s distal lower extremity pain is subserved by the saphenous nerve. If destruction of the saphenous nerve is being contemplated, ultrasound-guided saphenous nerve block with local anesthetic can provide prognostic information as to the extent of motor and sensory deficit the patient will experience following nerve destruction.

Ultrasound-guided saphenous nerve block with local anesthetic may also be used to provide postoperative pain relief following distal lower extremity surgeries and is useful in the treatment of persistent postoperative neuropathic pain following vein harvesting and stripping procedures. Electromyography can distinguish saphenous nerve dysfunction from lumbar plexopathy, lumbar radiculopathy, and diabetic polyneuropathy. Plain radiographs of the knee and distal lower extremity are indicated in all patients who present with saphenous neuralgia to rule out occult bony pathology. Based on the patient’s clinical presentation, additional testing may be warranted, including a complete blood count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging of the point of suspected nerve compromise is indicated if to clarify the diagnosis or if tumor, infection, or hematoma is suspected (Fig. 148.2). Ultrasound and computerized tomographic scanning are also indicated if mass or tumor is suspected or if the cause of saphenous nerve compromise is in question. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

The saphenous nerve is the largest sensory branch of the femoral nerve. The saphenous nerve provides sensory innervation to the medial malleolus, the medial calf, and a portion of the medial arch of the foot. The saphenous nerve is derived primarily from the fibers of the L3 and L4 nerve roots. The nerve travels along with the femoral artery through Hunter canal and moves superficially as it approaches the knee (Fig. 148.3). It passes over the medial condyle of the femur, splitting into terminal sensory branches. The saphenous nerve is subject to trauma or compression anywhere along its course. The nerve is frequently traumatized during vein harvest for coronary artery bypass grafting procedures. The saphenous nerve is also subject to compression as it passes over the medial condyle of the femur.

Ultrasound-guided block of the saphenous nerve at the knee can be carried out by placing the patient in the supine position with the arms resting comfortably across the chest and the affected lower extremity externally rotated (Fig. 148.4). A total of 8 mL of local anesthetic is drawn up in a 12-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic. A point ˜5 cm above the patella on the anteromedial femur is then identified by palpation (Fig. 148.5). A linear high-frequency ultrasound transducer is placed in a transverse plane over the previously identified point on the anteromedial femur, and an ultrasound survey scan is obtained (Figs. 148.6 and 148.7).


The hyperechoic anterior medial border of the femur will be visualized as well as the vastus medialis muscle just anteromedial to it. The ultrasound transducer is then slowly moved in a more medial direction until the sartorius muscle, which lies posteromedial to vastus medialis muscle, is visualized (Fig. 148.8). The saphenous nerve lies just in the fascial plane just below the sartorius muscle (Figs. 148.9 and 148.10). When the fascial plane below the sartorius muscle is identified on ultrasound imaging, the skin is prepped with anesthetic solution, and a 3½-inch, 22-gauge needle is advanced from the lateral border of the ultrasound transducer and advanced utilizing an in-plane approach with the trajectory being
adjusted under real-time ultrasound guidance until the needle tip is resting within the facial plane beneath the sartorius muscle in proximity to the saphenous nerve (Fig. 148.11). When the tip of needle is thought to be in satisfactory position, a small amount of local anesthetic and steroid is injected under real-time ultrasound guidance to confirm that the needle tip is correctly beneath the sartorius muscle in proximity to the saphenous nerve. There should be minimal resistance to injection. After needle tip placement is confirmed, the remainder of the contents of the syringe are slowly injected. The needle is then removed, and a sterile pressure dressing and ice pack are placed at the injection site.