The meniscal ossification observed in Dunkin Hartley guinea pigs may play an important role in the pathogenesis of OA in these animals.

Purpose: In animal models, the severity of cartilage damage is assessed by histological scores evaluating the structure, the proteoglycan content , the integrity of the tidemark, the cellularity, and osteophytes. In parallel to these histological analyzes, we studied the mechanical properties of cartilage at different stages of disease progression in the Dunkin-Hartley guinea pigs. We also correlated the severity of histo-logical lesions with the mechanical properties of cartilage. Methods: Sixty, male, 3-week-old Dunkin-Hartley guinea pigs from Charles River Laboratories (Paris, France) were used. Guinea pigs were randomized into 5 groups of 12 guinea pigs. At 4-week-old and every 8 weeks until week 36, twelve Hartley guinea pigs were sacrificed. Histo-logical severity of the lesion was evaluated using OARSI score and mechanical properties of cartilage were assessed by the MACH-1 technology (Biomomentum, Canada). To do this, the tibial plateaus and femoral condyles of 60 guinea pigs were taken. An indentation protocol and measurement automated thickness was applied to cover the entire artic-ular surface. The Young modulus (measure of the stiffness of the cartilage) and the thickness were calculated using the Mach-1 Analysis software. Results: Histological assessment of cartilage lesions showed that guinea pigs spontaneously developed severe knee osteoarthritis. In all animals, the global histological score increased significantly with age until week 28 (p < 0.0001 between week 4 and 28) and then stabilized (between weeks 28 and 36). The cartilage thickness gradually decreased until week 20 and then remained stable between weeks 28 and 36. A significantly positive correlation was observed between the global OARSI histological score and the young modulus (condyle: r ¼ 0.566, p < 0.0001; tibial plateau: r ¼ 0.442, p < 0.0012). Figure 2: Histological analysis of bone marrow lesions in Hartley guinea pigs. A e Graphical representation of average grade assigned based off of grading scale. B e Photo of bone marrow of a control animal at 3 months, C and D are examples of found bone marrow lesions. C e Fibrosis (black arrow). D e Encapsulated (red arrow) and non-encapsulated (black arrow) necrosis. Significant differences in thickness and young modulus between groups over time were observed. Abstracts / Osteoarthritis and Cartilage 25 (2017) S76eS444 S314