Minimum Effective Volume of Lidocaine-Bupivacaine for Subgluteal Block

Inclusion Criteria: * age between 18 and 75 years * American Society of Anesthesiologists classification 1-3 * body mass index between 20 and 35 Exclusion Criteria: * adults who are unable to give their own consent * pre-existing neuropathy (assessed by history and physical examination) * coagulopathy (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. platelets≤ 100, International Normalized Ratio≥ 1.4 or partial prothrombin time ≥ 50) * renal failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. creatinine ≥ 100) * hepatic failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. transaminases ≥ 100) * allergy to LA * pregnancy * prior surgery in the subgluteal region * chronic pain syndromes requiring opioid intake at home