- Indications: anterior thigh, femur, and knee surgery
- Transducer position: transverse, close to the femoral crease
- Goal: local anesthetic spread adjacent to the femoral nerve
- Local anesthetic: 10–20 mL
Transducer position and needle insertion using an in-plane technique to block the femoral nerve at the femoral crease.
The ultrasound-guided technique of femoral nerve blockade differs from nerve stimulator or landmark-based techniques in several important aspects. Ultrasound application allows the practitioner to monitor the spread of local anesthetic and needle placement and make appropriate adjustments, should the initial spread be deemed inadequate. Also, because of the proximity to the relatively large femoral artery, ultrasound may reduce the risk of arterial puncture that often occurs with this block with the use of non-ultrasound techniques. Palpating the femoral pulse as a landmark for the block is not required with ultrasound guidance, a process that can be challenging in obese patients. Although the ability to visualize the needle and the relevant anatomy with ultrasound guidance renders nerve stimulation optional, motor response obtained during nerve stimulation often provides contributory information.
Orientation begins with the identification of the pulsating femoral artery at the level of the inguinal crease. If it is not immediately recognized, sliding the transducer medially and laterally will bring the vessel into view eventually. Immediately lateral to the vessel, and deep to the fascia iliaca is the femoral nerve, which is typically hyperechoic and roughly triangular or oval in shape (Figure 35-2A and B). The nerve is positioned in a sulcus in the iliopsoas muscle underneath the fascia iliaca. Other structures that can be visualized are the femoral vein (medial to the artery) and occasionally the fascia lata (superficial in the subcutaneous layer). The femoral nerve typically is visualized at a depth of 2- to 4-cm.
(A) Cross-sectional anatomy of the femoral nerve (FN) at the level of the femoral crease. FN is seen on the surface of the iliopsoas muscle covered by fascia iliaca. (white arrows). Femoral artery (FA) and femoral vein (FV) are seen enveloped in their own vascular fascial sheath created by one of the layers of fascia lata. (B) Sonoanatomy of the FN at the femoral triangle.
- Identification of the femoral nerve often is made easier by slightly tilting the transducer cranially or caudally. This adjustment helps "brighten" up the nerve and makes it appear distinct from the background.
Femoral nerve block results in anesthesia of the anterior and medial thigh down to the knee (the knee included), as well as a variable strip of skin on the medial leg and foot. It also contributes branches to the articular fibers to both the hip and knee. ...