When local anaesthetic is injected into the psoas compartment it spreads behind the muscle up to the level of lumbar vertebra L4 and covers the terminal nerves of the lumbar plexus and the lumbosacral trunk of the sacral plexus.
Vertebral body L4 (V4), psoas major (pm), local anaesthetic (green asterix), neural foramen of vertebra L4 (yellow asterix).
