If good things come from above, do bad things come from below?

Factors in the synovial fluid that maintain healthy articular cartilage, such as hyaluronic acid and lubricin, come from above. Is it possible that factors which lead to the destruction of cartilage come from below in the subchondral bone? The recent acquisition of tools to probe early events in osteoarthritis is shedding new light on possible contributions from this compartment on the initiation and progression of the disease. Tanamas and co-workers now provide evidence that bone marrow lesions in the subchondral bone are predictive, both of loss of cartilage and of formation of subchondral cysts. These data provoke questions about the nature and role of bone marrow lesions.