The Mininimum Effective Anaesthetic Volume of Local Anaesthetic in Ultrasound-guided "Shamrock" Lumbar Plexus Block

The "Shamrock method" is a new ultrasound-guided lumbar plexus block. The aim of the study is to determine the minimum effective volume of ropivacaine 0.5% required to produce an effective lumbar plexus block with this method. Using the Dixon and Massey up-and-down method study design, 30 patients scheduled for elective total hip and knee arthroplasty will be included in the study.