The factors associated with pain severity in patients with knee osteoarthritis vary according to the radiographic disease severity: a cross-sectional study

Abstract

Knee osteoarthritis (OA) pain is suggested to be associated with inflammation and detrimental mechanical loading across the joint. In this cross-sectional study, we simultaneously examined the inflammation and alignment of the lower limb and examined how the pain components varied depending on the disease progression. One-hundred sixty female medial type of early- [n=74 in Kellgren-Lawrence (K/L) 2] to advanced-stage (n=96 in K/L >2) knee OA subjects (70.5 years on average) were enrolled. Knee pain was evaluated using a pain visual analog scale (VAS) and the pain-related subcategory of the Japanese Knee Osteoarthritis Measure (JKOM-pain). The serum interleukin (sIL)-6 level reflecting synovitis, and the high sensitivity C-reactive protein (hs-CRP) level were measured to evaluate the severity of inflammation. The anatomical axis angle (AAA) was measured as an alignment index. The β-coefficient was estimated after adjusting for age and the body mass index (BMI) using a multiple linear regression analysis. Multiple linear regression analyses showed that the sIL-6 levels, but not AAA, associated with the pain VAS [β=10.77 (95% confidence interval (CI): 4.14-17.40), P<0.01] and JKOM-pain scores [β=3.19 (95% CI: 1.93-4.44), P<0.001] in the early stage. Conversely, AAA, but not the sIL-6 levels, was found to be associated with the pain VAS [β=-1.29 (95% CI:-2.51 to-0.08), P<0.05] and JKOM-pain scores [β=-0.49 (95% CI:-0.82 to-0.16), P<0.01] in the advanced stage. The presence of a higher level of sIL-6 and the varus alignment of the joint is associated with pain in early- and advanced-stage knee OA patients, respectively.