Femoral Nerve Origin: • The femoral nerve is the largest branch of the lumbar plexus, and is formed from L2,3,4.
Femoral N. Anatomy Key Points: • VAN – vein, artery, nerve (from medial to lateral). • Nerve lies on top of iliopsoas muscles. • Nerve to sartorius m. exits and lies superficial and medial to main body of femoral n.
Fascia Lata • Note fascias lata and iliaca. Fascia iliaca lies between the artery and the nerve – thus they lie in different compartments.
Femoral Nerve Cutaneous Distribution • The femoral nerve supplies the anterior thigh and part of the medial thigh, then as the saphenous nerve supplies the medial aspect of the lower leg and ankle.
Knee & Hip Bone Innervation Anterior Posterior
Standard Femoral Block Technique • Palpate femoral artery at inguinal crease. • Mark a spot 1 cm lateral to pulse. • Advance needle till quadriceps twitch obtained.
Issues With Standard Technique: Body Size
Nerve to Sartorius m. Sartorious Twitch Issues With Standard Technique: • Injection should not be done when a sartorius twitch is present, because the nerve may have already exited the sheath.
Injection Outside Sheath: Issues With Standard Technique:
Femoral N. Ultrasound Imaging (1): Positioning: • Patient flat, stomach retracted with wide tape if needed. • Stand on side of block, machine on opposite side. • Try to line up needle, transducer, and US monitor – makes it easier to image your needle.
Femoral N. Ultrasound Imaging (2): Holding the Probe: • Notice the hand is holding the probe in a way that the side facing us is easily visualized – making it easier to get the needle lined up with the middle of the probe. • Notice that the hand is resting on the patient’s skin. This helps keep the probe from sliding around on the gel.
Imaging: • Start below crease. • Perpendicular to leg, not parallel to crease. • Look for femoral artery, white triangle. Yes! No!
Lateral Medial Try to identify the fascial planes and the nerve.
Fine Tuning Imaging: • Slight rotational and angle adjustments of probe, to get best cross section. • Move probe cephalad to find best compromise between femoral nerve image and depth. (As you move cephalad, the nerve becomes a more distinct bundle. However, it can be harder to image as it gets deeper.)
Medial Lateral Another example. Try to identify the fascial planes and the nerve.
Note second artery below femoral artery – the profunda femoris branch.
At this location, femoral nerve is also branching out, and harder to image, so best to move more cephalad.
Approaches: With Stimulation IP OOP
Approaches: No Stimulation • Here, an 18 g Touhy needle is being used – easier to see with US, and easier to feel the 2 pops through fascias lata and iliaca.
OOP IP Don’t aim for nerve. Aim to pierce fascia iliaca lateral to nerve. Feel fascial pop, then give 1 ml test dose to confirm location.
OOP Geometry A good goal for the OOP approach would be that your needle tip approaches the nerve at the point that the ultrasound beam intersects with the nerve. That way, you will be sure to see your test injection. You can measure depth to nerve with US, then use that information as shown.
Example of Out of Plane Approach Note that the needle isn’t seen here, but tissue movement shows general track of the needle.
In Plane – Outside Sheath An example of a test injection above the fascia iliaca, and probably also above the fascia lata.
Out of Plane – Outside Sheath An example of a test injection above the fascia iliaca.
Post injection. Even though nerve is not completely surrounded with local, the block is still usually good.
Scenario:Total Knee Replacement • Preop meds: celexecob, gabapentin • Spinal anesthesia • Femoral single shot block vs catheter • Pre or postop. • Local by surgeon (helps with sciatic mediated pain).