Objectives: Evaluate effectiveness and safety of using continuous adductor canal block (CACB) in patients undergoing ambulatory total knee arthroplasty (TKA), in comparison to single shot adductor canal block (SACB). Primary objective is assess the quality of recovery of those patients (using the 15-item quality of recovery scale - QoR-15) at predetermined time points postoperatively. Secondary objectives are to evaluate postoperative pain scores, postoperative use of opioid, opioid-induced adverse effects (measured via validated opioid symptom distress scale), postoperative functional status, complications relating to the perineural catheter and readmissions.

Hypothesis: Continuous adductor canal block would lead to a better quality of recovery in patients undergoing outpatient TKA.

Methods: Randomized controlled prospective trial, blinded for patient and evaluator, in patients undergoing outpatient primary TKA at Sinai Health. After Hospital's Ethics in Research Board approval, the recruitment will begin. Patients will be assessed about their eligibility for participating and after plain clear information about the study interventions they will or will not authorize their inclusion and data collection, through the signature of a written consent. The subjects will have their surgeries booked in advance and they will be submitted to the pre anesthesia consult at the Pre Admission Unit a few days before the surgery. The study proposal will be explained to the patients in that occasion. They will receive a booklet with information about the study and the Consent Form that they will bring home with them. They will have the time between the pre anesthesia assessment and the surgery (at least two days) to review and consent to the study. Patients will be randomized to one of the two groups using a computer-generated random numbers table. The randomization will be done before the beginning of the study and will define which study number is going to be managed as interventional group (continuous adductor canal block - CACB) or control group (sham continuous adductor canal block - ShACB). Each patient will receive a study number following the order of their entrance on the study. The elastomeric pumps to be used connected to the catheter will be previously prepared by hospital pharmacy, accordingly to the randomization made and the subject study number, with no identification of the content (NaCl 0.9% or Ropivacaine 0.2%). Hospital pharmacy will not be blinded for which study number and elastomeric pump will be linked to the study group. Research coordinator, professional who performs the adductor canal catheter insertion and researcher who collects the data will be blinded to which group each patient was randomized. After accordance to participate on the study, the patient will be randomized to one of the two studies groups: continuous adductor canal block (CACB) or sham continuous adductor canal block (ShACB). All patients will receive the same perioperative management. The only difference will be the postoperative continuous perineural infusion: the CACB group will receive an infusion of 0.2% ropivacaine 5mL/h and ShACB group will receive an infusion of NaCl 0.9% 5mL/h. Patients will initially be brought to a dedicated block room where a safety checklist will be performed by the block room team. Standard Canadian Anesthesia Society monitoring will be provided. Mild sedation with Midazolam 0.5-2mg and Fentanyl 25-100mcg might be administered for anxiolysis and analgesia. After proper cleaning of the ipsilateral thigh, under sterile technique and ultrasound guidance (Sonosite Edge II ultrasound machine), an adductor canal block (injection of 15 mL of Ropivacaine 0.5% with epinephrine 1:200,000) and an IPACK block (injection of 15 mL of Ropivacaine 0.25% with epinephrine 1:200,000) will be performed. Cumulative local anesthetic doses will be preemptively calculated to avoid a total Ropivacaine dose of \> 3mg/kg. After the peripheral nerve blocks, all patients will receive standard spinal or general anesthesia. All intraoperative opioids administered will be recorded. In the intra-operative period, each patient will receive IV Cefazolin 2g, Tranexamic acid 20mg/kg, Dexamethasone 0.1mg/kg, and Ondansetron 4mg. At the end of the procedure the surgeons will infiltrate the surgical site with 200 mg of Ropivacaine 0.2%. After surgery, the patient will be taken to the Post Anesthesia Care Unit. At this moment, an Arrow® (StimuCath® Continuous Peripheral Nerve Block Catheter) continuous adductor canal block catheter will be inserted using a Sonosite Edge II ultrasound machine. A bolus of 5-10mL of saline solution (NaCl 0.9%) with epinephrine 1:200,000 will be given, after negative aspiration, following adductor canal catheter insertion and the patient will be monitored for any heart rate change in order to rule out intravascular catheter placement. The catheter will be well secured with an adhesive fixation device to avoid displacement. Following catheter placement, the catheter will be aspirated to check for blood to ensure there is no intravascular placement.

The catheter will be aspirated prior to any injection including at the time of saline injection during catheter placement. The peripheral nerve catheter will be connected to a Baxter elastomeric pump. Depending on which group the patient is randomized to, the solution will be Ropivacaine 0.2% or Saline 0.9%. Infusion rate will be of 5mL/h. The patient will be discharged to home after achieving the discharge criteria, keeping the peripheral nerve catheter with the same infusion rate for the planed time. The adductor canal catheter will infuse for 48 hours. Prior to going home, patients will receive education and written information (educational pamphlet) regarding monitoring for local anesthetic systemic toxicity symptoms, possible CABC associated complications including potential transient muscle weakness, and instructions on patient removal of the catheter after 48 hours. This pamphlet will contain contact information for research team or Acute Pain Service, in case of any events, adverse effects or questions the patients may have about the peripheral nerve catheter. A phone number to contact each patient at home will collected before. Standard oral analgesic scheme will be prescribed to every patient (Acetaminophen 650mg QID, Celecoxib 200mg BID, Hydromorphone 1-2mg PRN Q4Hs).