Subchondral bone and cartilage disease - A rediscovered functional unit

The role of subchondral bone in the pathogenesis of cartilage damage has li kely been underestimated. Subchondral bone is not only an important shock a bsorber, but it may also be important for cartilage metabolism. Contrary to many drawings and published reports, the subchondral region is highly vasc ularized and vulnerable. Its terminal vessels have, in part, direct contact with the deepest hyaline cartilage layer. The perfusion of these vessels a ccounts for more than 50% of the glucose, oxygen, and water requirements of cartilage. Bony structure, local metabolism, hemodynamics, and vasculariza tion of the subchondral region differ within a single joint and from one jo int to another. Owing to these differences, repetitive chronic overloading or perfusion abnormalities may result in no pathological reaction at all in one joint, while in another joint, these same conditions may lead to osteo necrosis, osteochondritis dissecans, or degenerative changes. According to this common etiological root, similar pathological reactions beginning with marrow edema and necrosis and followed by bone and cartilage fractures, jo int deformity, and insufficient healing processes are found in osteonecrosi s, osteochondritis dissecans, and degenerative disease as well.