Malahias, MA, Birch GA, et al. - This study was undertaken to investigate whether perioperative synovial fluid or blood plasma cytokine levels are correlated with reduced early post-total knee arthroplasty (TKA) range of motion. This study enrolled a sum of 179 individuals with end-stage idiopathic osteoarthritis who had undergone TKA in this prospective cohort study. The obtained synovial fluid and blood plasma prearthrotomy and plasma was collected longitudinally in the postacute care unit and on postoperative days (PODs) 1 and 2. Stiffness was characterized as ≤ 95° range of motion assessed with a goniometer at 6 weeks (±2 weeks). The data indicate that there is a distinct acute postoperative cytokine response profile in individuals who establish stiffness 6 weeks after TKA. At the first 2 postoperative days, this profile was defined by significant differences in levels of 9 cytokines. These outcomes distinguish cytokines that are potential biomarkers for risk of early stiffness after TKA and may play a role in the pathophysiology of this outcome.