The Investigators aim to study the efficacy of Exparel as compared to Marcaine, taking into account pain control, narcotic consumption, narcotic-related side effects, outcomes measures, and patient satisfaction. Moreover, the Investigators plan to perform cost-benefit analysis to evaluate whether use of Exparel decreases analgesic consumption, duration of hospital stay and the need for physical therapy postoperatively, therefore, offsetting its higher price in comparison with Marcaine.

Inclusion Criteria:

All patients at least 18 years old who have primary unilateral TKA for osteoarthritis performed at Thomas Jefferson University Hospital.

Exclusion Criteria:

• American Society of Anesthesiologist (ASA) score of 4 or higher
• Hepatic disease (contraindication for acetaminophen)
• Renal disease (contraindication for NSAIDs)
• Any contraindication for oxycodone, ketorolac, epinephrine, pregabalin, gabapentin, hydromorphone, Tramadol, morphine or other narcotics that are considered as part of routine postoperative pain control protocol
• Fibromyalgia
• Any contraindication for intrathecal opioid injection
• History of substance abuse during the last 2 years
• History of allergy to amide compounds
• Current consumption of monoaminoxidase (MAO) inhibitors and tricyclic antidepressant (TCA) medications
• Allergy to metabisulfite compounds
• Chronic use of opioid medications in the month prior to surgery (leads to opioid tolerance and/or opioid-induced hyperalgesia)
• Body weight<50 Kg, BMI>40 Kg/m2
• History of hypotension
• Patients with any surgery related complication in the first 4-6 weeks following TKA, such as infection or mechanical failure