Characterizing Early Monoarthritis in Rats: A Pathological and Clinical Study of an Mbsa/cfa-induced Model

A comprehensive understanding of arthritis pathophysiology, involving inflammation, pain, and joint complications, is crucial for enhancing diagnostic accuracy and therapeutic approaches. This study examines the inflammatory mechanisms and clinical implications of arthritis. Male Wistar rats were subjected to arthritis induction in the right knee via intra-articular injection of mBSA/CFA. They were divided into a control group (CG, n = 10) and two arthritis groups (8-day – IG and 13-day – AG, n = 8 each) treated with tramadol at 17,8 mg/kg SC q.8 h. Histological and immunohistochemical analyses revealed an influx of inflammatory cells, mainly CD68 + macrophages. [18F] FDG PET/CT revealed increased intra-articular glucose metabolism. The data were analyzed via t tests, two-way ANOVA or two-way repeated-measures ANOVA, and Mann‒Whitney, Kruskal‒Wallis, or Friedman tests (p < 0.05). Both arthritis groups presented increased PGE ₂ and collagen I and V in the right knee, with clinical signs such as reduced weight bearing, weight loss, and increased pain, indicating inflammatory arthritis. During testing, the control group presented decreased movement and velocity but a greater rearing frequency than did the AG group. This study clarifies arthritis inflammation and affirms the importance of animal models in the development of better treatments. These findings also substantiate the efficacy of tramadol in alleviating arthritis-associated pain.