Continuous Versus Single Injection Adductor Canal Blocks for Outpatient Total Knee Arthroplasty

A Pilot Randomized Controlled Trial Assessing Pain and Opioid Outcomes Among Patients Undergoing Total Knee Arthroplasty Receiving 5-Day Outpatient Adductor Canal Continuous Versus Single Injection Blocks

This is a single-center pilot study to determine if an adductor canal continuous nerve block is superior to single injection nerve block following total knee arthroplasty. Investigators will randomize participants to either continuous nerve block or single injection nerve block for the adductor canal preoperatively. They will assess differences in pain (measured in numeric rating scale), opioid consumption, and physical therapy milestones from postoperative day 0 to 7.

Adductor canal blocks are standard care for postoperative analgesia following total knee arthroplasty. Adductor canal blocks involve depositing local anesthetic (ropivacaine) around the saphenous nerve at the location of the adductor canal on the ipsilateral thigh. At UCSD, the standard care is to perform single injection adductor canal blocks for research participants undergoing total knee arthroplasty prior to surgery in the preoperative waiting area.

Participants will be randomized to either: (1) single injection with ropivacaine (0.5%) of the adductor canal block AND a 5-day continuous perineural infusion of ropivacaine (0.2%) (experimental group); versus (2) single injection with ropivacaine (0.5%) of the adductor canal block and no continuous nerve block added.

Inclusion Criteria:

1. Adult participants of at least 18 years of age
2. Undergoing a primary, unilateral, total knee arthroplasty
3. Planned single-injection adductor canal nerve block
4. Weight > 50 kg (to minimize the risk of local anesthetic toxicity)

Exclusion Criteria:

1. chronic opioid or tramadol use: daily oxycodone equivalents > 20 mg for > 4 weeks
2. neuro-muscular deficit of the surgical limb
3. moderate pain (NRS > 3) in an anatomic location other than the surgical site
4. planned hospital admission following surgery
5. history of opioid misuse
6. those who lack capacity to complete informed consent
7. inability to contact the investigators during the treatment period, and vice versa (e.g., lack of telephone access)
8. incarceration
9. pregnancy
10. allergy to amide local anesthetics