Can Single-Injection Adductor Canal Blocks Improve PostOp Pain Relief in Patients Undergoing Total Knee Arthroplasty?

The purpose of the study is to determine the effect of a single injection adductor canal block (ACB) on pain scores within 24 hours post total knee arthroplasty (TKA).

Total knee arthroplasty (TKA), also known as total knee replacement, has been associated with a significant pain burden in the postoperative period. Methods to manage pain associated with this operation have in the past included injecting pain medication into the epidural space of the spinal cord, around a peripheral nerve, around the space surrounding the joint, or a combination of pain management techniques.

In recent years, the femoral nerve block (injection of pain medication around the peripheral nerve, specifically the femoral nerve) has been proposed as an effective way to manage pain while sparing many of the undesirable side effects of narcotic pain medications. Traditional techniques of the femoral nerve block involve the injection of pain medication around the peripheral nerve at the level of the groin area. A nerve block at this point in the path of the femoral nerve affects all of the musculature of the front part of the thigh as well as the nerves responsible for sensation to the majority of the knee joint. The femoral nerve block performed at the level of the groin provides an excellent level of pain relief at the knee joint, but is also associated with weakness of the quadriceps muscle. The resultant quadriceps weakness can both slow the physical therapy process and be a risk factor for post-operative falls. Participation in physical therapy is a critical component of the rehabilitation process and is started as soon as tolerated by the patient. The ideal pain management technique would provide the same degree of pain relief as the femoral nerve block while preserving the strength in the front part of the thigh muscles.

One suggested technique to achieve both of these goals is the injection of a large volume dilute local pain medication mixture around the joint during surgery. This has been used as a substitute to provide pain relief around the joint while maintaining strength in the quadriceps muscle and the ability to participate in physical therapy. This technique however, does not last long since the medication disperses away from the joint space.

A variation of the femoral nerve block in the lower thigh, within a space called the adductor canal, has been demonstrated to provide equivalent amounts of pain relief as a proximal femoral nerve block along with preservation of motor function to the quadriceps muscle. What is not as well-established is whether the combination of injecting pain medication directly around the joint space in the knee along with a single injection of pain medication in the adductor canal in the lower thigh can improve pain scores and extend the duration of pain relief provided compared to only an injection around the joint space.

Eligibility Criteria:
Inclusion Criteria:

* Males and Females age 18+ years old having total knee arthroplasty (TKA) at UCI Medical Center
* American Society of Anesthesiologists physical status I to III

Exclusion Criteria:

* Allergy to local anesthetics
* Pregnancy
* Nursing Mothers
* Children \<18 years of age
* Renal impairment (GFR\<60 mL/min/1.73m2)
* Hepatic Impairment (active hepatitis, elevated AST or ALT, jaundice)
* Opioid tolerant patients (defined as greater than 30 mg Morphine equivalent consumed daily)
* Patients that are diabetic with peripheral neuropathy
* BMI greater than 40