Figure 2

RGB trichrome staining of the cartilage-bone interface in osteochondromas. In growing osteochondromas (A–D), resembling the epiphyseal growth plate, the hyaline cartilage (HC) is undergoing endochondral ossification, showing calcified matrix (CC) at the bone interface, invasion by connective and vascular tissue (asterisks) and formation of bone trabeculae (B) containing a center of calcified cartilage, and occasional chondrocytes (Ch). The cement lines between bone and calcified cartilage can be observed (black arrows in C). Osteo(chondro)clasts (Oc) can be observed in the resorption zones. In non-growing osteochondromas (E–H), resembling articular cartilage, chondrocytes were sparse and non-hypertrophic, and a tidemark (white arrows) can be observed between uncalcified (UCC) and calcified (CC) cartilage matrix, as well as cement lines (black arrows) between cartilage and bone. In some areas, a direct contact between uncalcified cartilage and bone (black arrows in G) or reduplication of the tidemark (white arrows in H) can be observed.