Evaluation of Imaging, Histopathological and Serum Alarmin Findings in Rats with Non-Invasively Induced Post-Traumatic Osteoarthritis

Post-traumatic osteoarthritis (PTOA) develops following joint injury and involves inflammatory processes, including signaling by damage-associated molecular patterns (DAMPs). Standardized non-invasive PTOA induction protocols for rats remain limited. This study aimed to evaluate a newly developed, patented cyclic-loading device for non-invasive PTOA induction and to characterize joint alterations using imaging, histopathology, and serum DAMP measurements. Sixteen female Wistar albino rats (280–300 g) were assigned to control and PTOA groups (n=8/group). Under anesthesia, the left stifle of PTOA rats underwent 20 N cyclic loading in three sets of 40 cycles (120 cycles per session), three days per week for three weeks. The right hind limb served as an unloaded contralateral control. Gait, radiographic, and ultrasonographic assessments were performed in the third week. Serum high mobility group box 1 (HMGB1), serum amyloid A (SAA), S100 calcium-binding protein A8 (S100A8), and S100A9 were measured by enzyme-linked immunosorbent assay (ELISA), and joint tissues were examined histopathologically (n=4/group). Radiography and ultrasonography (USG) demonstrated irregular joint margins and narrowed joint spaces in loaded stifles. USG also indicated increased echogenicity in the joint cavity. Kellgren-Lawrence grades were significantly higher in the PTOA group (p<0.001). Gait parameters did not differ significantly between groups after multiple-comparison correction, although reluctance to walk and facial expressions suggestive of discomfort were qualitatively observed. Histopathology showed chondrocyte vacuolar degeneration in the PTOA group, with cartilage thinning, erosion, matrix fibrillation, or capsular thickening and inflammatory infiltration in some cases. SAA and S100A8 levels were higher in the PTOA group (unadjusted p=0.033 and 0.016), but neither difference remained significant after Holm–Šidák correction (adjusted p=0.095 and 0.063). HMGB1 and S100A9 levels were also higher, but not significantly. Imaging and histopathological findings suggest the patented device induced joint changes consistent with PTOA without surgical intervention, but longitudinal and mechanistic studies are needed to clarify the serum DAMP response.