الفهرس 
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Abstract
Introduction: Interleukin-21 is a proinflammatory cytokine that has a role in the pathogenesis of primary knee osteoarthritis. The aim of the study was to assess the relation between serum interleukin-21 and primary knee osteoarthritis severity regarding pain, stiffness, functional disability and structural damage.
Patients and methods: The study included 50 patients with primary knee osteoarthritis and 40 apparently healthy volunteers. Clinical examination was done. Western Ontario and Mcmaster Universities Osteoarthritis Index was used to assess primary knee osteoarthritis severity. Functional assessment of knee osteoarthritis was done using Health Assessment Questionnaire-Disability Index. Kellgren-Laurence grading scale was used to assess knee joint radiologically. Serum level of interleukin-21 was measured in both patients and control subjects.
Results: The study included 50 patients with primary knee osteoarthritis (44 females [88.0%]). The control group included 40 apparently healthy volunteers (33 females [82.5%]). There were no statistical significant differences between patients and control groups regarding gender (P=0.552) and age (P=0.068).
Serum interleukin-21 level was statistically significantly higher among the patients group in comparison to control group (P=0.008). There were statistical significant positive correlations between interleukin-21 serum level and Western Ontario and Mcmaster Universities Osteoarthritis Index stiffness subscale (P=0.050) and Health Assessment Questionnaire-Disability Index score (P=0.031). Serum interleukin-21 level was statistically significantly higher among patients group with knee joint line tenderness versus patients group without knee joint line tenderness (P=0.003).
Serum interleukin-21 level was statistically significantly higher among patients group with knee joint effusion versus patients group without knee joint effusion (P=0.005). There was statistically significant differences between patients with serum interleukin-21 level exceeded the reference cut-off value versus those with serum interleukin-21 level within the reference cut-off value regarding percentage of patients with knee joint effusion (P=0.043), Western Ontario and Mcmaster Universities Osteoarthritis Index pain subscale (P=0.044) and Western Ontario and Mcmaster Universities Osteoarthritis Index total score interpretation (P=0.004).
Conclusions: Serum interleukin-21 was significantly higher in patients with primary knee osteoarthritis. Serum interleukin-21 was positively correlated with Western Ontario and Mcmaster Universities Osteoarthritis Index stiffness subscale and Health Assessment Questionnaire-Disability Index.
Higher grades of Western Ontario and Mcmaster Universities Osteoarthritis Index scores, joint line tenderness and joint effusion were associated with patients with serum interleukin-21 level exceeded the reference cut-off value. Knee pain, stiffness, joint tenderness, effusion and osteoarthritis functional disabilities were related to interleukin-21.
Serum interleukin-21 could be a potential biochemical marker for primary knee osteoarthritis.