This is a multicenter, randomized, double-blind, placebo-controlled, study conducted in subjects undergoing unilateral TKA. Subjects will undergo a screening visit up to 28 days prior to surgery. A sufficient number of subjects will be enrolled to obtain at least 40 evaluable subjects. Upon enrollment, subjects will be randomized in a 1:1 ratio of ALGRX 4975 to placebo. Subjects will receive a femoral nerve block prior to induction of general anesthesia. Subjects will undergo total knee arthroplasty (TKA) under general anesthesia. Prior to closure of the surgical wound, a single dose of ALGRX 4975 5 mg in 60 mL or placebo will be instilled (dripped by syringe over approximately 1 minute) into the wound onto the cut muscles and soft tissues and allowed to dwell for 5 minutes. The Investigator will then inject bupivacaine 0.25% up to 40 mL into the area of the wound and cut muscles and close the wound by usual surgical procedures. Postoperative pain will be managed by morphine sulfate administered intravenously by patient controlled analgesia (PCA). Following discontinuation of the PCA pump, subjects will be provided with hydrocodone 7.5 mg/acetaminophen 500 mg for postoperative pain.