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Objective: Meniscus degeneration and subchondral bone changes contribute to the development and progression of knee OA. The purpose of this study was to reveal the relationship between medial meniscus degeneration and characteristics of subchondral bone changes in different models. Design: We used the anterior cruciate ligament transection (ACL-T) model, destabilization of the medial meniscus (DMM) model, controlled abnormal tibial translation (CATT) model and a controlled abnormal tibial rotation (CATR) model with different mechanical stresses. We performed histological analysis and micro computed tomography analysis, at 4 and 6 weeks. In addition, we divided the tibial subchondral bone into four compartments and set the regions of interest. Results: Meniscus degeneration was observed in all groups, but there was no significant difference. The ACL-T group showed posterior displacement of the contact area, and the DMM and CATR groups showed lateral deviation of the medial meniscus. The region-specific subchondral bone changes in each model showed that changes in mechanical stress due to ACL and meniscus dysfunction, as well as changes in the contact area, affect the bony structure of the subchondral bone differently in each region. Conclusions: Subchondral bone changes in different models of mechanical stress were different in each region. In particular, changes in the contact area and increased compressive stress due to meniscus dysfunction were suggested to promote bone formation. The results of this study indicate that changes in alignment and contact area in the PTOA model may cause region-specific characteristics of the subchondral bone changes.

Objective: Mechanical stress is one of the most exacerbating factors on knee osteoarthritis (OA). We recently reported the effect of shear stress on OA progression in vivo using controlled abnormal tibial translation (CATT), which suppressed shear stress in vivo due to ACL transection (ACL-T). However, surgical ACL-T mice models were used, thus effect of shear stress cannot be clarified exactly. So, we aimed to establish a novel Non-Invasive ACL-T without intra-articular injuries and reveal the onset mechanism of knee OA induced by shear stress. Design: First, twelve-week-old C57BL/6 male mice were used to make a novel Non-Invasive ACL-T model. After creating the model, injuries of intra-articular tissues were observed histologically, macroscopically, and morphologically. Next, twelve-week-old C57BL/6 male mice were categorized into ACL-T, CATT, and Sham groups. After 2,4 and 8 weeks, we performed the anterior drawer test, safranin-O/fast green staining, and immunohistochemical staining for MMP-3 and TNF-α. Results: In a novel Non-Invasive ACL-T model, no injuries, including cartilage, meniscus, and bone were not observed except ACL rupture. Regarding OA progression, the anterior tibial translation in the ACL-T group was significantly higher than that of the other groups at all weeks, and cartilage degeneration in the ACL-T group increased significantly compared with the other groups at 8 weeks. Although synovitis score in the ACL-T and CATT groups was significantly higher than the Sham group at 2 and 8 weeks, there were no differences between the ACL-T and CATT groups. In addition, the MMP-3 positive cell rate in the cartilage of the ACL-T group was higher than the other groups at 4 and 8 weeks. However, that in the synovium of the ACL-T group was higher than the other groups at 8 weeks. TNF-α positive cell rates in both cartilage and synovium were not changed between the ACL-T and CATT groups. Conclusion: We have successfully established a new Non-Invasive ACL-T model without intra-articular tissue damage, which induces knee OA due to shear stress. In the OA progression caused by shear stress, chondrocytes first showed a molecular biological response, leading to a local increase in MMP-3. On the other hand, synovitis is not directly induced by mechanical stress but is indirectly caused by intra-articular degeneration associated with knee OA progression.