Participants in this group will receive intraoperative analgesia via application of ZYNRELEF (HTX-011) directly into the periarticular tissues at the surgical site following prosthesis implantation and prior to capsule closure. The medication will be applied by the surgeon using sterile technique per manufacturer instructions, targeting the posterior capsule, medial and lateral gutters, and surrounding soft tissues.

Participants in this group will receive a postoperative ultrasound-guided adductor canal block performed by a board-certified anesthesiologist or regional anesthesia-trained provider. The procedure will be conducted under sterile conditions while the patient remains under spinal anesthesia.

A single 14 mL dose of HTX-011 containing 400 mg bupivacaine and 12 mg meloxicam will be applied intraoperatively to the surgical site. This FDA-approved formulation is designed to provide sustained analgesia for up to 72 hours following total knee arthroplasty.

Mean cumulative milligram morphine equivalents (MME) administered at 4, 8, 12, 16, 20, 24, 48, and 72 hours following total knee arthroplasty (TKA). Values will be compared between patients receiving Zynrelef and those receiving adductor canal block (ACB)

Pain scores assessed 4 hours after surgery and at 6 weeks follow up using the Visual Analog Scale (VAS) for pain assessment consists of a line drawn in the form of a ruler, and numbers from 0 to 10 (with 0 as "no pain" and 10 as "unbearable pain"