Knee pain is a very common symptom of knee osteoarthritis (OA), and identification of the major contributors to knee pain is important to establish management plans for patients with knee OA. Among the potential contributors, we hypothesized that coexisting depressive symptoms might increase the severity of knee pain because the increased cytokine levels and neurotransmitter changes related to depression are known to influence the threshold of physical pain perception. Therefore, a possible relationship between self-reported depressive symptoms and self-reported knee pain has been explored. Additionally, we sought to determine factors influencing the severity of knee pain in a middle-aged and elderly Korean population using data from the fifth Korean National Health and Nutrition Examination Survey.
In total, 6599 persons aged ≥50 years were evaluated in terms of the radiographic severity of OA and pain severity using 10-point numerical rating scales. Depressive mood was assessed using a polar question: "Had the subject felt despair or depression every day for more than 2 weeks during the past year?"
The Kellgren-Lawrence knee OA grade, depression, gender, educational level, household income, smoking status, marital status, living place, comorbidity status, BMI, and age were identified by multiple linear regression as variables affecting knee pain severity. The presence of depressive symptoms was associated with an increased risk of severe knee pain (odds ratio 2.55 [95 % confidence interval 1.77-3.66]). After stratifying the group in terms of the radiographic severity of knee OA, the relationship with depression persisted in the minimal (2.89 [1.90-4.32]) and moderate OA subgroups (2.29 [1.33-3.94]), but not in the severe OA subgroup.
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Severe knee pain was independently associated with the presence of depressive symptoms in middle-aged and elderly Korean subjects. This suggests that screening for and treatment of depression may help improve knee pain in elderly individuals.