While the properties of joint fluid may affect the tribology of joint replacement prostheses, the flow parameters of joint fluid have not yet been examined in the context of total knee arthroplasty (TKA). The objective of this study was to evaluate the flow properties of joint fluids in patients undergoing index TKA or revision TKA. We hypothesized that an alteration of the properties of joint fluid would result from TKA. The steady-shear viscosity and storage and loss moduli were evaluated in joint fluid from 35 arthritis patients undergoing TKA, 14 patients undergoing revision of a previous TKA, and two patients presenting with joint effusion after TKA. The same properties were also evaluated in two commercially available sodium hyaluronate preparations and bovine serum, which is used as a lubricant in joint simulators. The steady-shear viscosity varied over three orders of magnitude among samples obtained from patients undergoing TKA, spanning previously established "normal" and "diseased" ranges. Fluid obtained at index TKA was more likely to exhibit normal viscous properties than fluid obtained at revision TKA (p = 0.01). Other viscous parameters distinguished the two groups, but the difference did not reach statistical significance. Both groups exhibited degenerate flow properties when compared to synovial fluid from healthy individuals. Further examination of the connection between flow properties and the tribology of joint replacement prostheses is warranted.