Abstract: Objective  To study the effect of autologous platelet rich plasma (PRP) injection combined with etoricoxib in the treatment of knee osteoarthritis (KOA) and its impact on cytokines. 
Methods  Sixty-eight patients with KOA were selected and divided into single group (n=34) and combination group (n=34) according to random number table. The single group was treated with etoricoxib, and the combination group was treated with autologous PRP injection and etoricoxib. At 6 weeks after treatment, the efficacy of the two groups was compared. Before treatment and at 6 weeks after treatment, the two groups were compared in terms of osteoarthritis index ［Western Ontario and McMaster University Osteoarthritis Index (WOMAC) score］, Lyshom Knee Rsting System (Lysholm) score, quality of life ［Index of Severity Forosteo Arthritis (ISOA) score］ and cytokines ［interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), high-sensitivity C-reactive protein (hs-CRP)］, and incidence of adverse reactions during treatment. 
Results  The total effective rate of combination group was higher than that of single group (P＜0.05). At 6 weeks after treatment, WOMAC score, ISOA score, IL-1β, TNF-α, and hs-CRP level were lower than those before treatment, while Lysholm score was higher than that before treatment; WOMAC score, ISOA score, IL-1β,TNF-α, and hs-CRP level were lower in the combination group than in the single group, and the Lysholm score was higher than that of the single group (P＜0.05). There was no significant difference in the incidence of adverse reactions between two groups (P＞0.05). 
Conclusion  The application of autologous PRP injection combined with etoricoxib in the treatment of KOA has an obvious effect, which can alleviate the inflammatory reaction of bone joints, improve the function of knee joints and quality of life, and regulate the level of cytokines, with high safety. 

Key words: osteoarthritis, knee, platelet-rich plasma, etoricoxib