The purpose of this study is to determine feasibility of this study design and identify barriers that altered design could bring to overcome these barriers in the design of a large, pragmatic, multi-center clinical trial. It is also designed to estimate the effect size and variance of the main outcome measures, trust and fear, in patients undergoing rehabilitation after total knee arthroplasty (TKA). The study team hypothesizes that intramuscular (IM) oxytocin, in a dose and time determined by a series of previous studies under this grant to target the brain, will enhance trust and reduce fear and that these will be associated with improved outcomes. Again, the study is not designed to test this hypothesis, but to gather the critical data necessary to test it in a large, multi-center clinical trial that would follow this grant.~Participants that have decided to undergo unilateral TKA, will come to the Pain Clinical Research Unit at least 48 hours prior to surgery to confirm consent and complete a series of questionnaires. Participants surgery, anesthesia, and postoperative medication and therapy treatment will be routine. On the first outpatient study visit participants will complete a questionnaire of fear about pain and receive an intramuscular injection of oxytocin or placebo in a randomized, double blind manner. At the end of this session participants will complete a questionnaire assessing the degree of trust in the therapist. Physical therapy be will routine, and the fear and trust questionnaires will be completed at the 2nd, 4th, 8th, and last physical therapy session as well as routine measures of progress and function. The primary outcome measure is assessment of effect size and variability of the trust and fear questionnaires on the 1st and 2nd visit.
This study will examine the effect that a dose of intramuscular (IM) oxytocin (naturally occurring hormone) has on fear of pain and movement and trust in the physical therapist during outpatient rehabilitation after total knee replacement has been performed. Investigators will ask participants to answer questions about fear of pain and movement before several outpatient physical therapy session and investigators will ask participants questions about trust of the physical therapist several times after the outpatient physical therapy sessions.