Meniscal regeneration after resection of the anterior half of the medial meniscus in mice.

Various animal studies have indicated that reduced meniscal function significantly exacerbates articular-cartilage degeneration. Despite the importance of meniscal function for joint homeostasis and prevention of osteoarthritis, the healing process after meniscal injury and the regenerative process after meniscus removal have not been studied in detail. In this study, we examined the process of meniscal regeneration and cartilage degeneration after meniscectomy in mice. The left anterior halves of the medial menisci in male C57Bl/6J mice were resected, and histological assessment of the process of meniscal regeneration was conducted on day 3 and 2, 4, and 6 weeks after the surgical procedure. Extensive macrophagic infiltration into the synovial membrane around the meniscectomized area was observed on day 3. Synovial hyperplasia was detected 2 weeks after the operation. At this stage, synovial tissue was filled with many fibroblastic cells, which underwent chondrocytic differentiation and produced cartilage matrices by 4 weeks after the operation. At 6 weeks, regenerated tissues resembled those of an intact meniscus. The articular cartilage at the interface of the resected meniscus significantly degenerated between 2 and 4 weeks after the surgical procedure, but subtle progression in cartilage degeneration was observed between 4 and 6 weeks. This finding is suggestive of a balance between meniscal regeneration and cartilage homeostasis.