The basic science of the subchondral bone

Abstract

In the past decades, considerable efforts have been made to propose experimental and clinical treatments for articular cartilage defects. Yet, the problem of cartilage defects extending deep in the underlying subchondral bone has not received adequate attention. A profound understanding of the basic anatomic aspects of this particular site, together with the pathophysiology of diseases affecting the subchondral bone is the key to develop targeted and effective therapeutic strategies to treat osteochondral defects. The subchondral bone consists of the subchondral bone plate and the subarticular spongiosa. It is separated by the cement line from the calcified zone of the articular cartilage. A variable anatomy is characteristic for the subchondral region, reflected in differences in thickness, density, and composition of the subchondral bone plate, contour of the tidemark and cement line, and the number and types of channels penetrating into the calcified cartilage. This review aims at providing insights into the anatomy, morphology, and pathology of the subchondral bone. Individual diseases affecting the subchondral bone, such as traumatic osteochondral defects, osteochondritis dissecans, osteonecrosis, and osteoarthritis are also discussed. A better knowledge of the basic science of the subchondral region, together with additional investigations in animal models and patients may translate into improved therapies for articular cartilage defects that arise from or extend into the subchondral bone.

Elevated Expression of Periostin in Cartilage in Early Experimental Osteoarthritis

“…However, in the current study, Postn expression levels were markedly increased in the cartilage at 1, 2 and 4 weeks post-surgery. Although the mechanism that induced the difference of expression of Postn between between subchondral bone and cartilage remained unknown, different mechanical force on the two tissues may involve in [16,17]. Specially, up-regulated Postn cartilage cells mainly located in the superficial zone of articular cartilage, however, in the deeper zone of cartilage, the positive staining was rarely detected, supporting our hypothesis that Postn expression induced by pathologic forces on cartilage.…”

“…In the OA model used in this study, knee joint surgical instability induced pathologic overload forces. As we known, the surface layer of cartilage is exposed to higher pathologic pressure and shear stress than deeper layer of cartilage and the subchrodral bone [17,18]. Additionally, Postn is a secreted protein synthesized by osteoblasts and chondrocytes and it could participate to the crosstalk between subchondral bone and cartilage and it may involve different signaling pathways in different tissue [14].…”

Alterations of the subchondral bone in osteochondral repair – translational data and clinical evidence

“…Osteochondral defects disrupt the structural integrity of the subchondral bone, but the natural history of the restoration of the subchondral bone plate in these defects is not well understood (Gomoll et al, 2010b;Madry, 2010;Madry et al, 2010;Orth et al, 2013a;Pape et al, 2010). Besides constituting the new cartilaginous repair tissue, mesenchymal cells in the deeper regions of the defect also differentiate into osteocytes (Jackson et al, 2001;Shapiro et al, 1993), resulting in the formation of immature bone that usually restores the original level of the subchondral bone in a distinct chronological order (Orth et al, 2012a).…”

Management of Knee Articular Cartilage Injuries

“…Although most of the collagen in articular cartilage is Type II (90% -95%), there is a small amount of Type X collagen found in this zone, as it is associated with hypertrophic chondrocytes and calcification of cartilage. Beneath the calcified cartilage layer, separated by a thin cement line, is the subchondral bone, consisting of a lamellar cortical bony endplate and underlying cancellous trabeculae (Madry, van Dijk et al 2010). Chondrocytes produce the entirety of the content of the ECM, including proteoglycans, collagen, and non-collagenous proteins.…”