Osteoarthritis early-, mid- and late-stage progression in the rat medial meniscus transection model.

Osteoarthritis is a degenerative disease of synovial joints affecting all tissues, including articular cartilage and subchondral bone. Osteoarthritis animal models can recapitulate aspects of human disease progression and are used to test efficacy of drugs, biomaterials, and cell therapies. The rat medial meniscus transection (MMT) model is a surgically induced posttraumatic osteoarthritis model commonly used for preclinical therapeutic screening. We describe herein, the qualitative and quantitative changes to articular cartilage, subchondral bone, and formation of osteophytes at early-, mid-, and late-stages of osteoarthritis progression. Tibia of MMT-operated animals showed proteoglycan loss and fibrillation along articular cartilage surfaces as early as 3-weeks post-surgery. With contrast-enhanced micro-CT technique, quantitative, 3-dimensional analysis of the tibia showed that the articular cartilage thickened at 3- and 6-weeks post-surgery and decreased at 12-weeks post-surgery. This decreased cartilage thickness corresponded with increased lesions in the articular cartilage that led to its full degradation and exposing the subchondral bone layer. Further, subchondral bone thickening was significant at 6-weeks post-surgery and followed cartilage damage. Osteophytes were found as early as 3-weeks post-surgery and coincided with articular cartilage degradation. Cartilaginous osteophytes preceded mineralization, suggesting endochondral ossification. The rat MMT model has predominantly been used out to 3-weeks, and most studies determined the effect of therapies to delay or prevent the onset of osteoarthritis. We provide evidence that an extension of the rat MMT model out to 6- and 12-weeks more resembled severe phenotypes of human osteoarthritis. Thus, evaluating novel therapeutics at late-stage will be important for eventual clinical translation.