Depth-dependent biomechanical analysis of articular cartilage in the murine DMM model

Objectives Osteoarthrosis (OA) is the world’s leading disease of the musculoskeletal system. Injuries or altered joint loads by obesity is a main factor for cartilage degradation and thus OA progression. It is a complex, whole joint disease in which multiple factors play a significant role. To investigate the cartilage biomechanics during OA progression, the destabilizing medial meniscus (DMM) model is used. In this model, the medial meniscus of mice is dissected and OA begins to develop due to overloading.

Several studies already analyzed the biomechanics of the degenerating cartilage in the DMM model, but they all measured it on top of the cartilage facing the superficial zone or on later OA states down to the middle zone. However, cartilage is spatially divided into the superficial/middle and deep zone. For that reason, the present study showed for the first time the depth-dependent biomechanical alterations during early murine OA progression.

Methods DMM surgery was performed on 12-week-old male mice (C57BL/6) and knee samples were collected 2 and 8 weeks after surgery. Sham operated knees were used as a control. Snap-frozen murine knee samples were cut into 20 µm tissue sections and placed on a glass slide with an adhesive tape. The biomechanical analysis was performed with an atomic force microscope (AFM) (NanoWizard I, JPK Instruments) using a 20 nm, pyramidal-shaped tip (MLCT, Bruker) mounted on an optical microscope (Axiovert, Zeiss) allowing the precise placement of the cantilever. In the three different articular cartilage zones (superficial, middle and deep zone), of the medial tibia plateau, 25x25 force curves were assessed over a scanning area with a lateral size of 3 µm in three adjacent areas. The Young’s modulus was than calculated by fitting the Hertz-Sneddon model on the approaching part of the curve up to a maximum indentation depth of 500 nm.

Results and Conclusion Assessment of the 2 weeks sham-operated mice showed an two-fold increase in Young’s modulus from the superficial to the deep zone, whereas the DMM-operated mice showed an approximately two-fold higher Young’s modulus in all zones compared to sham. The 8 weeks sham-operated mice showed a 1.5-2.5 fold increase in each zone compared to the 2 weeks sham-operated. The DMM showed only a slight stiffness increase from 2 weeks to 8 weeks. Comparing the 8 weeks DMM and sham, the DMM is still slightly stiffer in the middle and superficial zone, while the deep zone is marginally softer. In general, none of the assessed samples showed an OARSI score higher than 2 and thus no severe OA. In conclusion, the articular cartilage shows a stiffness gradient, an overall stiffening with aging and a significant stiffening in the DMM model that starts to diminish in OA progression. This leads to the assumption that the significant Young’s modulus increase in the DMM model 2 weeks after surgery is probably one of the first signs of onsetting arthrosis.

Stichwörter AFM DMM osteoathrosis nanoindentation articular cartilage stiffness

Publication History

Article published online:
15 October 2020