BackgroundKnee osteoarthritis (KOA) is increasingly more prevalent and significant number of patients require knee arthroplasty. Although knee arthroplasty is generally successful, it takes months to recover physical function. Preoperative physical function is known to predict postoperative outcomes and exercise can improve preoperative physical function. However, patients with KOA have difficulty exercise on land due to pain and stiffness, while water exercise can be better tolerated. We hypothesized that preoperative water exercise to improve preoperative physical function will improve postoperative outcomes after total knee arthroplasty (TKA).MethodsWe enrolled 43 participants who were scheduled for elective TKA in 4–8 weeks and scored at or below 50th percentile in mobility assessment tool-sf (MAT-sf). All enrolled participants were assessed on 1) clinical osteoarthritis symptom severity using Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), 2) physical function using Short Physical Performance Battery (SPPB), 3) self-reported mobility using Mobility Assessment Tool-short form (MAT-sf), 4) depression using Geriatric Depression Scale-short form (GDS-sf), 5) cognitive function using Montreal Cognitive Assessment (MoCA). Blood samples for high-sensitivity-C-reactive protein (hs-CRP), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) were stored at − 80 °C then all samples were analyzed together. All the enrolled participants were randomly assigned to the aquatic exercise intervention (AEI) or usual care group. Sixty minute sessions of AEI was conducted three times a week for 4–8 weeks. Participants in both groups were evaluated within 1 week before their scheduled surgery, as well as 4 weeks after the surgery.ResultsThe mean age was 67.1 (±6.2), 44% were female, 74% were White. There is no statistically significant difference in combined outcome of any complication, unscheduled ER visit, and disposition to nursing home or rehab facility by AEI. However, AEI was associated with more favorable outcomes: WOMAC scores (p < 0.01), chair-stand (p = 0.019), MAT-sf as well as improved depression (p = 0.043) and cognition (p = 0.008).Conclusion4–8 weeks of aquatic exercise intervention resulted in improved functional outcomes as well as improved depression and cognition in elderly patients undergoing TKA. A larger study is warranted to explore the role of water exercise in clinical and functional outcomes of TKA.