Cartilage degradation in osteoarthritis: A process of osteochondral remodeling resembles the endochondral ossification in growth plate?

Osteoarthritis (OA) is one of the most common degenerative disease which causes pain and disability of joint and brings heavy socioeconomic burden in the world. However, the pathogenesis of OA has not been fully understood. Articular cartilage degradation or loss was often regarded as the characteristic of osteoarthritis. But we believe that there may had a illusion that OA was simply considered to be a process of wear and tear because evidences have supported all joint tissues remodeling including cartilage, subchondral bone, synovium, ligament, fat pad, and etc, were engaged in OA, in particular the cartilage and subchondral bone. Many factors such as mechanics, inflammation and immunological abnormality could drive the joint tissues metabolic and disturb the steady state of cartilage and bone, which further devoted to a serial pathological manifestations, consisting of hypertrophy and apoptosis of articular chondrocytes, degradation of cartilage matrix, angiogenesis and calcification of hyaline cartilage, replication of tidemark, formation of osteophytes, degeneration of ligaments and, in the knee, the menisci, hypertrophy of the joint capsule and remodeling of subchondral bone along with increased permeability of the osteochondral interface. The thickening of calcified cartilage, the thinning of superficial hyaline cartilage and the remodeling of subchondral bone indicated that the cartilage degradation could be a procedure of enchondral ossification similar to the growth plate, of driven by a host of cytokines within the affected joint. Articular cartilage loses stable state from normal resting to a high turnover in the stimulation of abnormal mechanical stresses and cytokines would subsequently contributed to slowly sustained remodeling and calcification, which might be the key features of the initiation and development of OA. In this article, the development and structural comparison of articular cartilage and growth plate as well as the major pathologic features of OA will be discussed to explain that cartilage degeneration in OA might be a process of enchondral ossification similar to growth plate. This would provide a new perspective for understanding OA's pathogenesis and the treatment in the future.