Mapping Articular Cartilage Biomechanical Properties of Normal and Osteoarthritis Mice Using Indentation

Materials and Methods: The biomechanical measurements were performed ex vivo, on the left femoral condyles and tibial plateaus of five healthy Balb/c males (age of 12-15 weeks) and five age- and sex-matched STR/ort mice, using a 3-axis mechanical tester equipped with a multiple-axis load cell. Indentation measurements (30-42/cartilage surfaces) were performed using a 0.35 mm diameter spherical indenter (30 um indentation in 1 second with 20 second relaxation). Following biomechanical testing, the articular surfaces were fixed in 4% paraformaldehyde for histological assessment. Data reported is the structural stiffness at indentation death of 10m. To compare the structural stiffness between healthy and OA-developing animals each articular surface were divided into 4 regions, outer medial half (I), inner medial half (II), inner lateral half (III) and outside lateral half (IV). Data is reported as the mean ± SE for each of these regions. Statistical analysis performed by ANOVA.

Results: In healthy animals, mapping of the structural stiffness at an indentation depth of 10 um showed a spatial distribution similar to that of larger animals (Fig 1 insert). The mean structural stiffness on the lateral condyle (zone III: 5.1±0.3 N/mm, in four regions of the condyles and tibial plateaus (Fig 1 and 2), (mean ±SE, n=2 animals) was similar on the lateral condyles and plateaus of the healthy and OA mice. In contrast, in OA mice the stiffness for the medial condyles (Fig.1) and plateaus (Fig.2)