Femoral Versus Adductor Canal Continuous Peripheral Nerve Blocks for Knee Arthroplasty

Patients typically experience moderate-to-severe pain following knee arthroplasty that is usually treated with a combination of oral and intravenous analgesics and enhanced by continuous peripheral nerve blocks. There are currently two locations to place a perineural catheter to provide analgesia following knee arthroplasty: a femoral nerve catheter and an adductor canal catheter. Both have been demonstrated to be effective following knee arthroplasty. However, it remains unknown if one location is superior to the other; or, more accurately, what the relative benefits are to each technique. While femoral CPNB has many benefits, one of the challenges of using this technique is that there is a decrease in quadriceps muscle strength which can be a limiting factor for rehabilitation. In contrast, the adductor canal catheter affects only the vastus medialis. This block may lessen block-induced quadriceps weakness following knee arthroplasty compared with a femoral infusion. The investigators hypothesize that compared with femoral perineural local anesthetic infusion, an adductor canal infusion is associated with a shorter time until four discharge criteria are met: (1) adequate analgesia; (2) independence from intravenous analgesics; (3) ability to ambulate 30 m; and (4) ability to stand, walk 3 m, and return to a sitting position without another's assistance.

Of importance: The primary investigation involves 80 evaluable subjects (with primary endpoint data) having tri-compartment knee arthroplasty. In addition, the investigators will enroll up to 70 subjects having uni-compartment knee arthroplasty as a pilot study in preparation for a subsequent larger, definitive trial. These two groups will not be analyzed together--they represent two distinct studies: one a definitive RCT for tri-compartment knee arthroplasty; and, one a pilot study for uni-compartment knee arthroplasty.

The control group will receive an adductor canal nerve block and postoperative ropivacaine 0.2% infusion

Discharge readiness is the number of hours until meeting the following 4 criteria: (1) adequate analgesia (defined as pain less than 4 on a NRS of 0-10); (2) independence from intravenous analgesics; (3) ability to ambulate 30 m and (4) ability to stand, walk 3 m, and return to a sitting position without another's assistance.

The time in hours until adequate analgesia is defined as pain less than 4 on a Numeric Rating Scale of 0-10, with 0=no pain and 10=worst imaginable pain

The time in hours until no intravenous analgesics were required for at least 12 hours (without future intravenous use during admission)

The timed-up-and-go (TUG) test measures the ability and speed of standing from a sitting position, walking 3 meters and returning to the original seated position independent from the assistance of healthcare personnel. This variable measured the time in hours until the patient could successfully achieve this test independently, regardless of the amount of time required.

The time in hours until a patient could ambulate at least 30 meters independently (regardless of time to achieve the 30 meters)

The amount of pain evaluated using the 0-10 Numeric Rating Scale with 0=no pain and 10=worst imaginable pain

Inclusion Criteria: primary, unilateral knee arthroplasty age ≥ 18 years postoperative analgesic plan includes perineural local anesthetic infusion of 48-72 hours Exclusion Criteria: morbid obesity as defined by a body mass index >40 (BMI=weight in kg/ [height in meters] chronic, high-dose opioid use (greater than 20mg oxycodone-equivalent opioid use daily within the 2 weeks prior to surgery and duration of use >4 weeks) history of opioid abuse allergy to study medications known renal insufficiency (creatinine > 1.5 mg/dL) pregnancy incarceration any known neuro-muscular deficit of the ipsilateral femoral nerve, obturator nerve and/or quadriceps muscle (including diabetic peripheral neuropathy); and inability to ambulate 30 m preoperatively.

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