Ethical statement: This study was conducted in accordance with the principles of the Declaration of Helsinki, International Committee on Harmonization of Good Clinical Practice Guidelines, and applicable local laws and regulations. This observational study was approved by the Institutional Review Board of our institution. Informed consent was obtained from all patients before enrolment in the study.
Patients and methods: The study included 20 knees of 19 patients who underwent TKA for rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), or knee osteoarthritis (OA). The inclusion and exclusion criteria are shown in Table 1. The patients were categorized into OA (OA, 11 knees) and non-OA (RA, 8 knees; SLE, 1 knee) groups.
Synovial and postoperative drainage fluid were collected from each patient according to the clinical study schedule shown in Table 2. During surgery, the synovial fluid was collected using an 18G needle and syringe before making a skin incision. Surgery was performed using standard techniques and a drainage tube was placed in the joint. To prevent the degradation of NGF and related molecules, a protease inhibitor cocktail (Nacalai Tesque, Kyoto, Japan) was added in advance to the drainage bottle, and the bottle was kept ice-cooled immediately after surgery until the time of drainage removal. Postoperative drainage fluid that accumulated in the drainage bottle until the time of drainage removal was collected on postoperative days 1, 2, and 14. Blood sampling was performed according to the study schedule and 20 mL of blood was collected at each time point. Preoperative blood sampling was conducted 1–3 days before surgery.
Routine blood tests were conducted, including hematological (e.g., hemoglobin, white blood cell count, white blood cell differential count, platelet count, and other complete blood counts) and blood chemistry tests (e.g., ALP, total bilirubin, albumin, AST, ALT, total protein, and other general biochemical parameters, as well as HBV, HCV, and HIV) (data not shown).
The NGF concentration was measured using an ELISA kit (Biosensis, BEK-2212). Cytokines were measured by an ELISA kit for interleukin (IL)-1β (R & D Systems, DLB50), tumor necrosis factor (TNF)-α (R&D Systems, HSTA00E), and IL-6 (R & D Systems, D6050). Lipid mediators were measured using liquid chromatography–tandem mass spectrometry as described previously [18].
Data analyses: Statistical analyses were performed using GraphPad Prism 10.1. (GraphPad Software, Inc., San Diego, CA, USA). Data are expressed as the mean ± SEM. Multiple groups were compared using one-way ANOVA followed by Dunnett’s test. Non-paired groups were compared using an unpaired t-test.