Lumbar plexus block is described as a difficult block, thus requiring experienced practitioners. Many techniques have been used to date, notably anatomical landmarks, neurostimulation, and ultrasound-guided techniques. Among ultrasound-guided techniques, the "Trident" technique was described in 2006, while the "Shamrock" technique was described in 2013. Trident consists in putting the probe sagittally next to the lumbar spine and injecting local anesthetic around the lumbar plexus inside the psoas muscle at the level of L4. It is an out-of-plane puncture.

Shamrock puts the probe transversely on the iliac crest. Authors of the 2013 article said the image obtained with this technique was an image of L4. This technique allows an in-plane puncture, which is a safe technique.

This study aims at describing the level obtained with Shamrock, as well as at comparing depth of lumbar plexus, image quality and presence of vessels between the two techniques.

Inclusion Criteria:

• Adult with indication of lumbar echography

Exclusion Criteria:

• Antecedent of spine surgery or spinal malformation

Adult with indication of lumbar echography will be included.