The purpose of this prospective research study is to determine the best way to manage post-operative pain after a total hip arthroplasty. Currently, there is no standard of care for managing post-operative pain in these patients. The quadratus lumborum block (QLB) first described by Blanco in 2007, is a promising technique in this indication: recently, there is a growing evidence for the use of the QLB as an alternative technique for pain management after hip surgery.