Nociceptin/Orphanin is a novel opioid peptide system associated with inflammatory response. Currently is it uncertain as to the presence of absence of nociceptin in synovial fluid of patients. Nociceptin levels will be measured pre-operatively and post-operatively in plasma levels of patients receiving primary total knee arthroplasty. Nociceptin levels will also be measured in synovial fluid levels prior to surgical manipulation.

This is a prospective observational study where nociceptin levels will be drawn from the patient's serum as well as from the patient's synovial fluid. The blood draws will be completed by the anesthesia team and the synovial fluid and tissue will be obtained by the orthopedic team. The initial blood draw will be in the preoperative area and the second blood draw will be five minutes after the release of the tourniquet. The synovial fluid will be drawn by the surgeon with the first incision. There will be no randomization nor control group.

Endpoints:

1. The level or absence of nociceptin in synovial fluid in patients receiving total knee primary arthroplasty will be measured via ELISA in picograms per volume.
2. The level or absence of nociceptin in plasma in patients receiving total knee primary arthroplasty both in the preoperative period (less than 1 hour prior to surgery and 5 minutes after the tourniquet is removed) via ELISA in picograms per volume.
3. Determine the changes if any of nociception plasma levels during the perioperative course of patients receiving total primary knee arthroplasty.

Secondary Study Endpoints:

1. Determine the effect if present of history of chronic pain and opioid use on the levels of nociception present in patients' synovial fluid and plasma receiving primary total knee arthroplasty.
2. Determine the effect if present of demographic factors on the levels of nociception present in patients' synovial fluid and plasma receiving primary total knee arthroplasty

Inclusion Criteria:

• receiving a primary knee joint arthroplasty by Dr. Davis ages 18-80 years hemodynamically stable no joint or other types of infection informed consent received and signed no prior joint arthroplasty at the current surgical site no other surgical intervention planned

Exclusion Criteria:

• prior knee arthroplasty at site outside of desired age range pregnant current infection in joint or other location no desire to participate

Sequential patients receiving primary unilateral knee arthroplasty by the same surgeon