Comparing Femoral Nerve Catheters to Single Shot Femoral Nerve Blocks for Total Knee Replacement Surgery

The study will be a randomized controlled blinded study with a sham control arm. The patients will be randomized to either a single shot FNB with placement of a catheter on the skin (sham control) or a conventional CFNC with catheter.

The group with SSFNB will receive a femoral nerve block before the surgery in the pre-operative area guided by a nerve stimulator and ultrasound. A bolus of 0.5 % ropivacaine will be injected around the femoral nerve. A catheter would be placed on the skin, without penetration, with occlusive dressing applied over the site. A standard size saline bag will be placed on the pump but will not be turned on. The tubing will be opaque and a bag will be placed over the pump to blind the patient to the medication, or lack of medication, being administered. The patient, nursing staff and physical therapists will be blinded to the presence of a sham catheter. The infusion will be labelled 'Study Drug R' or 'Study Drug N' in the electronic medicine prescription.

The group randomized with active drug by CFNB would have a continuous femoral catheter placed using nerve stimulator and ultrasound. Catheter will be bolused with 0.5 % ropivacaine around the femoral nerve and occlusive dressing applied over the catheter.

After placement of the femoral nerve block patients will be transported to the operating room and spinal anesthesia with bupivacaine and fentanyl will be performed. Intra-operative sedation of propofol infusion will be titrated to the discretion of the anaesthesia team. Patients will receive scheduled as well as rescue analgesia as per clinical pathway protocol.

Patients with CFNB will receive ropivacaine 0.2% infusion (the infusion rate will be dependent on the clinical judgement of the anaesthesiologist) in the post anaesthesia care unit (PACU) after the spinal anaesthesia has worn off. The infusion will be continued for the duration of the catheter, 4am POD one. Patients with SSFNB will not receive any infusion through the sham catheter.

The catheters will be removed on post-operative day (POD) one at about 8 am. Patient's pain score using visual analogue score (VAS) will be assessed. Functional status will be assessed by the physical therapist on POD one. The therapist will assess and document the distance walked, assistive device used, level of assist needed to ambulate, and knee proprioception or continued recommendation of the knee immobilizer.

Patients will be assessed in the PACU and POD 1 and 2. Recordings will be made of total opioid consumption in morphine equivalents, VAS score from 0-10 both at rest and on participation in physical therapy, incidence of nausea and vomiting and functional status during physical therapy.

Inclusion criteria

• Adults (18-80 years old)
• Scheduled to undergo primary unilateral TKA with Parapatellar approach
• Patient agrees to participate in the study
• Effective femoral nerve block
• No contraindication for spinal or regional anesthesia

Exclusion criteria

• History of opioid dependence or current chronic analgesic therapy (daily use >4 weeks
• Allergy to study medications
• Known hepatic or renal insufficiency/disease
• Peripheral neuropathy
• Morbid obesity (BMI >40 kg/m2)
• Unable to comply with study protocol
• Pregnancy
• Incarceration