Intra-Venous Acetaminophen and Muscle Relaxants After Total Knee

This research will be a prospective, three-arm, randomized, open-label trial to assess opioid use and patient reported outcomes after 48 hours of regular IV acetaminophen and muscle relaxant (IVAM) orphenadrine administration following total knee replacement surgery. 180 patients (60 in each arm) will be randomized to receive the standard group treatment, the IVAM group treatment, or to the control grouptreatment.

Standard Group Treatment: includes peripheral nerve single injection or catheter infusions (48 hours) as requested by the surgeon; preoperative (single dose) intravenous acetaminophen (1000 mg) and orphenadrine (60 mg); intraoperative spinal anesthesia or general anesthesia as determined by the anesthesia attending physician; postoperative oral oxycodone (5 mg) with acetaminophen (325 mg) (PRN dosing), oral orphenadrine (100 mg) every 12 hours for 3 doses, and intravenous hydromorphone (PRN dosing) for breakthrough pain.

Control Group Treatment: includes peripheral nerve single injection or catheter infusions (48 hours); preoperative (single dose) intravenous acetaminophen (1000 mg) intraoperative spinal anesthesia or general anesthesia as determined by the anesthesia attending physician; and postoperative oral oxycodone and acetaminophen (PRN dosing), and intravenous hydromorphone (PRN dosing) for breakthrough pain.

IVAM Group Treatment: includes peripheral nerve single injection or catheter infusions (48 hours); preoperative intravenous acetaminophen (1000 mg) and orphenadrine (60 mg); intraoperative spinal anesthesia or general anesthesia as determined by the anesthesia attending physician; postoperative intravenous acetaminophen (1000 mg) every 6 hours routine for total of 8 doses and intravenous orphenadrine (60 mg) every 12 hours for total of 4 doses; oral oxycodone (5 mg) (PRN dosing), and intravenous hydromorphone (PRN dosing) for breakthrough pain.

Inclusion criteria

• Age 18-85
• Primary, unilateral total knee arthroplasty
• American Society of Anesthesiologist (ASA) physical status I, II, or III

Exclusion criteria

• Chronic pain (as determined by regular opioid use in the month preceding surgery)
• Preoperative use of centrally acting muscle relaxants in the 24 hours preceding surgery
• Peripheral regional anesthesia procedures other than femoral nerve injections or catheters for postoperative pain control (such as popliteal block)
• Severe renal dysfunction, creatinine > 2.0
• Allergy or other contraindications to use of orphenadrine and/or acetaminophen
• Pregnant or breast feeding
• Abnormal Liver Function Tests(LFT) and / or history of chronic/excessive alcohol abuse.
• History of Hepatitis, B or C,
• History of cirrhosis or hepatic insufficiency