With the patient in the lateral decubitus and the block side independent, a curvilinear ultrasound transducer (2-5 MHz) will be directed caudally in a sagittal plane 3-4 cm lateral to the lumbar spinous process of L4, which is almost opposite to the iliac crest, producing a longitudinal scan of the lumbar paravertebral region; and thus identifying the transverse processes of L3 and L4, with PM muscle in-between and erector spinae muscle posteriorly.

The probe is shifted slowly to the lateral side until the transverse processes disappear and the QL muscle is evident in its long axis attached caudally to the iliac crest with a characteristic sonographic image of three muscle layers appearing from posterior to anterior as: erector spinae, QL, and PM muscles respectively. After subcutaneous local infiltration with lidocaine at the cephalic end of the probe, the block needle is advanced in a cephalo-caudal direction, through the erector spinae and QL muscles, until it pierces the epimysium of the QL. LA is injected anterior to the QL muscle, observing its spread in a caudal direction towards the iliac crest between the QL and psoas muscles