Muscular-based and patient-reported outcomes differentially associate with circulating superoxide dismutases and cytokines in knee osteoarthritis.

Muscular (i.e., quadriceps) weakness contributes to disease progression and precedes the appearance of patient-reported symptoms, such as pain and perceived physical dysfunction, in knee osteoarthritis (OA). It is unknown, however, if muscular-based and patient-reported outcomes differentially associate with systemic biomarkers reflective of the local mediators in knee OA. The purpose of this study was to identify if muscular-based and patient-reported outcomes differentially associate with circulating superoxide dismutase (SOD) and cytokines in knee OA. Subjects (n = 29) with pain, muscular weakness, and radiographic evidence (Kellgren-Lawrence grade ≥2) of knee OA in the involved (INV) leg were included in this study. Serum Cu/Zn and Mn SOD and cytokine concentrations were measured in fasting blood samples. Pain and physical dysfunction were subjectively assessed and muscle strength (i.e., peak isometric force and torque, and peak isokinetic-concentric knee-extension and -flexion torques) was determined unilaterally in the INV and non-involved (NI) legs. Peak isometric and peak isokinetic-concentric knee-flexion torques in the INV leg correlated with serum Cu/Zn SOD (both p < 0.05). Peak isometric force and torque and peak isokinetic-concentric knee-extension and -flexion torques in the INV leg correlated with serum Mn SOD (all p < 0.05). Pain and dysfunction inversely associated with serum IL-1β, IL-4, IL-5, IL-12, IL-13, and/or IFN-γ (p < 0.05). Neither SOD associated with pain or dysfunction, and none of the cytokines associated with muscular-based outcomes. We conclude that common outcome measures used in the clinical evaluation of OA differentially associate with circulating SOD and cytokines.