Femoral Versus Adductor Canal Continuous Peripheral Nerve Blocks for Knee Arthroplasty

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.

Inclusion Criteria:

1. primary, unilateral knee arthroplasty
2. age ≥ 18 years
3. postoperative analgesic plan includes perineural local anesthetic infusion of 48-72 hours

Exclusion Criteria:

1. morbid obesity as defined by a body mass index >40 (BMI=weight in kg/ [height in meters]
2. 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)
3. history of opioid abuse
4. allergy to study medications
5. known renal insufficiency (creatinine > 1.5 mg/dL)
6. pregnancy
7. incarceration
8. 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.