Total knee arthroplasty (TKA) is associated with severe postoperative pain. Multimodal analgesia, including peripheral nerve block, is recommended for post-operative pain relief 1. Perineural analgesia offers the advantage of extended pain relief up to 24 hours after surgery2.

This is a prospective, randomized control trial designed to compare the analgesic efficacy of the adductor canal block (ACB) performed immediately before or immediately after primary total knee arthroplasty (TKA). The primary objective of this study is to measure pain score associated with knee motion following TKA among patients receiving ACB as part of their analgesic regimen for TKA. Secondary end points include assessment of postoperative ambulation, range of motion, pain at rest, opioid consumption, and patient satisfaction between the two analgesic approaches. The investigators hypothesize that ACB before the surgery will reduce a patient's postoperative pain and improve patient satisfaction.

All consecutive patients undergoing primary TKA will be recruited for enrollment in the study. Patients will be for randomized preoperatively to receive either preemptive ABC (PreACB) or postoperative ABC (PostACB). Patients randomized to the PreACB group will receive the block prior to incision. Patients randomized to the PostACB group will receive the block at the end of the surgery. Both techniques are in accordance to the standard of care at our institute. All patients will have the ACB done by a regional anesthesiologist in the regional anesthesia unit, or in the operating room. Patient medical history will be obtained and blocks will be placed per usual protocol. Operative and anesthetic details, including medications given, will be recorded.

Pain scores and pain medications given in the PACU will be recorded. Supplementary analgesics will be provided per institutional PACU protocol. Study data will be recorded for up to 72 hours or until patient discharge. A follow-up will occur in 4- 6 weeks at the orthopedic follow-up appointment to evaluate the patient's late pain scores and overall satisfaction. Data will be analyzed both at the conclusion of the study and at several intervals prior to completion of the study.

D. Research Design and Methods

Inclusion Criteria:

The study is a prospective, randomized controlled clinical trial comparing two methods of regional analgesia for primary TKA. All adult primary TKA patients are eligible for inclusion in the study.

Exclusion criteria:

• Allergy to local anesthetics or to systemic opioids
• Contraindication to regional anesthesia technique, such as local infection or coagulopathy
• Sensory/motor disorder involving operative limb
• Requirements of more than 30 mg morphine equivalent daily prior to surgery
• ASA 4 or greater
• Psychiatric or cognitive disorders
• Incarceration
• Renal insufficiency with Cr > 2.0
• Hepatic failure
• Pregnancy
• Age under 18 years Potential risks for the procedure, which will be explained to the patient, include: bleeding, local infection, local anesthetic toxicity. All are commonly listed as rare complications of the procedures.

After consenting to participation and upon randomization, ACBs will be placed either in the regional anesthesia bay or the OR prior to anesthesia induction and surgery, or in the OR immediately upon completion of surgery.

For participating patients, the following data will be collected by the research staff: ASA physical status, age, height, weight, gender, intra- and post operative quantitative opiate use (expressed as morphine equivalent), numeric VAS scores, KSS score (form included) and QoR score (form included).

Those collecting data will be blinded from randomization of patients to either research group.

Intraoperative care:

Intraoperative anesthesia will be achieved using a general anesthetic technique. Intraoperative analgesia will be administered per anesthesiologists' discretion.

All patients will have cemented total knee utilizing a medial parapatellar approach, including patellar resurfacing. A tourniquet will be used in all cases. Posterior capsule infiltration will be done with 20cc of 0.25% bupivacaine, as the preferred method of providing sacral plexus analgesia 5-6, per current institutional protocol.

ACB Procedure Details Patients will lie in the supine position. The needle insertion site, approximately 10cm proximal to their operative knee, will be exposed. The skin will be disinfected with 2% Chlorhexidine and the ultrasound probe placed in a sterile sleeve. The femoral artery is identified with a high frequency linear transducer (Philips 4-12L linear transducer with a frequency of 6-12 MHz, Milwaukee, WI or ) proximal to the operative knee. The appropriate location for injection will be determined by following the femoral artery cephalad until the artery is directly posterior to the Sartorius muscle. At this level, the saphenous nerve is located lateral to the femoral artery. An 18g insulated sonographic Tuohy needle (Pajunk GmbH, Geisingen, Germany) will be inserted in an in-plane approach, under constant ultrasound visualization, through the Sartorius muscle to a final location in close proximity to the saphenous nerve. Once satisfied with needle placement and following negative aspiration, 20 cc of 0.5% ropivacaine will be injected gradually through the needle under visualization, with recurrent aspirations to verify absence of intra-vascular injection signs.

Data Collection Patients will be enrolled for the study during the orthopedic surgical appointment upon the scheduling of the surgery. Upon enrollment, patients will complete a baseline KSS questionnaire (attached), have a VAS pain score recorded, and have their pre-operative analgesic medication documented.

To assess the effect of pain with movement and overall strength, on POD 1, the patient will indicate their level of pain using VAS numeric scale (1-10). QoR questionnaire (attached) will be assessed 24 hours from the placement of the ACB. Overall analgesic medication consumption, both opioid (expressed as morphine equivalent) and non-opioid will be recorded for PODs 1-3.

The patients will also complete the KSS and the QoR questionnaires at the 4-6 week orthopedic follow-up appointment, as VAS scores and total analgesic medication will be documented.

Inclusion Criteria:

The study is a prospective, randomized controlled clinical trial comparing two methods of regional analgesia for primary TKA. All adult primary TKA patients are eligible for inclusion in the study.

Exclusion Criteria:

• Allergy to local anesthetics or to systemic opioids
• Contraindication to regional anesthesia technique, such as local infection or coagulopathy
• Sensory/motor disorder involving operative limb
• Requirements of more than 30 mg morphine equivalent daily prior to surgery
• ASA 4 or greater
• Psychiatric or cognitive disorders
• Incarceration
• Renal insufficiency with Cr > 2.0
• Hepatic failure
• Pregnancy
• Age under 18 years