## 4 Discussion  
### Mechanical Properties  
Studies comparing the mechanical properties between arthritic menisci and arthritis-free menisci are largely lacking. The confined and unconfined compression tests can only examine individual points of menisci. In addition, when the tissue is punched out, it is largely destroyed [10; 11; 13]. [PERSON] et al. [14] performed an indentation test of the meniscus which did not damage the integrity of the tissue. However, only three points were measured per meniscus, and therefore, a complete mapping of the biomechanical properties is missing. Previous studies could show that a complete mapping of biomechanical properties of articular cartilage [22; 25] and menisci [18] using indentation tests is possible. In the present study, we used an indentation test which allows a complete testing over the entire meniscus without leaving damage to the tissue.  
Using this method, we showed that there was a tendency for a greater tissue stiffening in the arthritic menisci, which was mainly apparent from the statistically significant difference in the  
Figure 8: Histogram of all arthritis-free SO stained sections (**A**); Histogram of all arthritic SO stained sections (**B**).  
Figure 9: Scatterplot with adjustment line concerning the correlation between SO score and IM over the posterior horn of the meniscus (**A**) and the entire meniscus tissue (**B**) for all samples (arthritic and arthritis-free).  
maximum applied load between the two groups (with \(p<0.05\)). Although the difference does not seem to be large at 0.01 N, it should be noted that this does not correspond to the surface load over the entire meniscus. These data represent the average value of the measured points with a diameter of the indenter of 1 mm. The maximum applied load to the arthritic menisci was 33% greater than that applied to the arthritis-free menisci. In other words, this means that although arthritic menisci can withstand a third-higher load or require a 33% greater force for a comparable deformation to the nonarthritic menisci, they also lose 33% of their damping properties. The findings of this study that the stiffness of the meniscus is increasing under OA support previous studies. [PERSON] et al. [30] could show that the axial compressive strains in menisci and meniscal root attachments significantly increased in severely degenerated knee joints compared with mildly degenerated knees. [PERSON] et al. [31] observed increasing mechanical properties of the meniscus' extracellular matrix under OA.  
Especially the posterior horn is affected by OA. The maximum applied load on the posterior horn of the arthritic menisci was twice as high as the arthritis-free menisci. The damping behavior was so reduced by half. This can be explained by the special type of rolling sliding movement in the knee joint [4]. This movement is caused by an increased mechanical load on the posterior horn of the meniscus, of which the posterior horn of the medial meniscus is most affected [32]. A study investigating the load distribution in medial menisci concluded that the posterior horn bears the highest percentage of shear stress [33]. Furthermore, the findings of [PERSON] et al. [34] suggest that the degenerative processes initially occur in the posterior horn. Under increased stress, stiffness seems to worsen in the particularly stressed regions of the meniscus, i.e., the posterior horn.