The purpose of this study is to determine which technique for catheter placement in continuous femoral nerve block (FNB) is most successful - guidance with (1) ultrasound or (2) nerve stimulation and ultrasound. Sensory and motor assessment scores will be obtained post-FNB. Patient controlled analgesia and opiate consumption is also recorded along with pain scores for the first 48 hour post-FNB.

Continuous femoral nerve block (cFNB) is a widely used regional anesthetic technique for many lower limb operations, such as total knee arthroplasty (TKA), anterior cruciate ligament repair, tibial osteotomy and patellar surgery. It provides superior pain relief, faster ambulation, shorter hospital stays and less risk of side effects in comparison to patient controlled analgesia (PCA), local anesthetic wound infiltration, or single shot femoral nerve block (FNB).

Stimulating catheters were introduced in 1999 to provide an objective end point to guide continuous nerve block catheter position by maintaining the desired evoked muscle response with nerve stimulation (NS). The main advantages of stimulating catheters are faster onset of sensory and motor block and reduction of local anesthetic drugs consumption. In recent years the precise insertion of continuous catheters has improved especially with the introduction of ultrasound (US)-guided imaging to regional anesthesia practice and advances in scanning techniques. That led to a call to reduce cost by switching to non-stimulating catheters. However, most studies comparing both catheters lacked anesthetic technique standardization and adequate sample size.

In this prospective randomized controlled trial, we compared postoperative analgesic efficacy and opioids consumption in patients having cFNB insertion using US alone and that of US combined with NS.

Inclusion Criteria:

• American Society of Anesthesiologists physical status I to III patients
• Aged 18-75 scheduled for unilateral TKA

Exclusion Criteria:

• History of significant psychiatric problems
• BMI > 40 kg/m^2
• Prior surgery in the inguinal region
• Neurological disease with sensory or motor deficit
• Diabetic neuropathy
• Contraindication to any study medications
• Daily opioid consumption >10 mg PO morphine (or equivalent) for 2 weeks prior to surgery