Indications

Anatomic considerations

Sensory and motor supply to the lower extremity is more elaborate than that of the upper extremity and involves two separate plexii (lumbar and sacral).

Organization of the lumbar and sacral plexii

The lumbar plexus is formed by the union of the first four lumbar spinal nerves which reunite within the substance of the psoas major muscle, in a fascial plane termed the "psoas compart-ment" where it can be approached via a posterior route through the quadratus lumbarum muscle. It supplies four nerves to the anterior part of the lower extremity, the femoral, lateral cutaneous, obturator and genitofemoral nerves. The psoas and iliacus muscles are enveloped by the same aponeurosis, the fascia iliaca sheath. At their emergence from the psoas muscle, all lumbar plexus nerves run a variable part of their course just below this fascia. Consequen-tly, an injection of adequate volume of local anesthetic within the inner surface of this fascia will result in blockade of the plexus components enveloped by the iliaca sheath. This is the anatomical concept behind the technique of the fascia iliaca compartment block.

The femoral nerve is the main branch of the lumbar plexus. It emerges from the psoas major muscle in the groove separating the psoas and the iliacus muscles, passes behind the inguinal ligament and enters the groin in the femoral triangle (Scarpa's triangle), lateral to the femoral vessels from which it remains separated by the lower part of the psoas major muscle. Of note, the femoral nerve does not enter the perivascular sheath, contrary to the brachial plexus which is contained in the perivascular sheath in the axilla. The main division branch of the fe-