Bone and Cartilage

Abstract

Cartilage and bone are intricately linked throughout life. The cells of both cartilage and bone develop from a common mesenchymal precursor. Furthermore, cartilage often serves as an intermediate precursor to bone in both embryonic development and adult wound repair. As a result of the intimate relationship between cartilage and bone, disease and damage to one tissue often results in phenotypic changes in the other. This relationship speaks of a constant communication between the cartilaginous and osseous tissues which extends beyond the developmental stage. As a result, it is important to consider both tissues when devising repair strategies. Articular Cartilage Structure and Function In the adult, hyaline cartilage covers the subchondral bone to provide a lubricating surface for joint movement as well as resistance to compressive and tensile forces. Chondrocytes, the cells in cartilage, and their extracellular matrix are organized in distinct zones related to their proximity to the subchondral bone. Each zone has a characteristic matrix composition and organization in addition to a unique cell density and morphology. Directly adjacent to the bone is a layer of calcified cartilage which consists of hypertrophic chondrocytes. These hypertropic cells express a variety of factors including Type X collagen and serve as an intermediate between the layers of cartilage and bone. 1 Moving away from the subchondral bone and calcified cartilage layers are the deep, middle, and superficial zones of cartilage, respectively. The deep zone is organized of alternating columns of cells and matrix which run perpendicular to the articular surface.