Elemental Changes in Synovial Fluids of Knees with Grade 0 and Grade 4 Osteoarthritis

Background: Oxidative stress and disturbed tissue homeostasis contribute to the pathogenesis of gonarthrosis, and trace elements act as cofactors or inhibitors of the antioxidant enzyme systems involved; data on elemental alterations in synovial fluid nevertheless remain scarce. This study aimed to reveal the changes in the elemental composition of synovial fluid in gonarthrosis. Methods: This prospective study included 64 patients: 33 with Kellgren–Lawrence grade 0 knees who underwent arthroscopy for meniscopathy (non-OA comparison group) and 31 with grade 4 gonarthrosis who underwent total knee arthroplasty (osteoarthritis group). Fifteen elements (Ca, Cu, As, Se, Sr, Sb, Hg, Al, Mn, Fe, Co, Ni, Zn, Cd, Pb) were measured in intraoperatively collected synovial fluid by inductively coupled plasma mass spectrometry (ICP-MS). Results: Between-group differences were confined to selenium and strontium. Mean selenium was 49.1 µg/L in the non-OA comparison group versus 37.6 µg/L in the osteoarthritis group (mean difference 11.5 µg/L; 95% CI: 4.15–18.9; p = 0.003), and strontium was 18.6 versus 22.3 µg/L, respectively (mean difference −3.70 µg/L; 95% CI: −6.20 to −1.20; p = 0.005). Mean iron was higher in the osteoarthritis group (3710 versus 3000 µg/L), but the difference was not significant (p = 0.051). Conclusions: In this exploratory cross-sectional comparison, synovial fluid selenium was lower and strontium was higher in grade 4 knees relative to grade 0 knees; however, these differences were attenuated after adjustment for age, and only selenium remained significant after Bonferroni correction. The remaining measured elements, including the toxic metals, did not differ between groups.