Automated Indentation of Femoral and Temporomandibular Joints for Characterization of Cartilage Tissue Quality in Fgf2 KO Mice.

PURPOSE: Degenerative disorders affecting the mandibular condylar cartilage (MCC) of the temporomandibular joint (TMJ), and the articular cartilage (AC) of the knee joint, are common chronic conditions. Fibroblast Growth Factor 2 (FGF2) is a critical growth factor in maintaining knee joint homeostasis; however, there are no studies on its role in maintenance of the TMJ. While a common, qualitative, approach to assess the integrity of the knee AC and TMJ MCC is histological evaluation, there is value in mechanical indentation as it provides complementary, quantitative data. The objectives of this study were to implement and employ an automated indentation technique to characterize potential topographical variation of structural stiffness over the surface of murine femoral AC and TMJ MCC and assess the effect of fibroblast growth factor 2 (FGF2) expression.

METHODS: Experiments were performed using 3-months-old female homozygote Fgf2KO mice with wide type (WT) littermates (each N=6). All procedures were approved by the Institutional IACUC. After euthanization, one mandible and hindlimb from each animal was processed for histology, while the other side was used for automated indentation on a Biomomentum Mach-1 v500csst with a 3-axis motion controller in a bath of PBS using a 0.3mm spherical tip indenter. Structural stiffness was calculated and mapped at multiple positions on the AC and MCC.

RESULTS: Global Fgf2KO lead to flattening of AC compared to WT (A,B) and indentation of the AC was able to demonstrate both regional variation in structural stiffness and differences between WT and Fgf2KO mice (C,D,E). Values for Fgf2KO were significantly smaller than WT at both the Medial/Anterior and Medial/Posterior positions. Global Fgf2KO also lead to a slight decrease in MCC thickness of the TMJ compared to WT (F,G) and structural stiffness values for Fgf2KO were significantly smaller than WT MCC at the posterior location (H,I,J).

CONCLUSIONS: Automated indentation is a sensitive, rapid, and non-destructive method that can be employed on both murine femoral AC and TMJ MCC to quantitatively characterize the tissue quality. This method was able to resolve differences in structural stiffness between WT and Fgf2KO tissue, demonstratingFGF2 expression affects cartilage integrity in these joints. This quantitative method, when combined with other histological and molecular biology methods, provides a valuable toolkit for characterization of murine cartilage tissue.